Oracle Interview Questions

1. What are the components of physical database structure of Oracle
database?

Oracle database is comprised of three types of files. One or more datafiles, two or more redo log files, and one or more control files.

2. What are the components of logical database structure of Oracle
database?

There are tablespaces and database’s schema objects.

3. What is a tablespace?
A database is divided into Logical Storage Unit called tablespaces. A tablespace is used to grouped related logical structures together.

4. What is SYSTEM tablespace and when is it created?
Every Oracle database contains a tablespace named SYSTEM, which is
automatically created when the database is created. The SYSTEM tablespace
always contains the data dictionary tables for the entire database.

5. Explain the relationship among database, tablespace and data file.
Each databases logically divided into one or more tablespaces one or more data files are explicitly created for each tablespace.

6. What is schema?
A schema is collection of database objects of a user.

7. What are Schema Objects?
Schema objects are the logical structures that directly refer to the database’s data. Schema objects include tables, views, sequences, synonyms, indexes,clusters, database triggers, procedures, functions packages and database links.

8. Can objects of the same schema reside in different tablespaces?
Yes.

9. Can a tablespace hold objects from different schemes?
Yes.

10. What is Oracle table?
A table is the basic unit of data storage in an Oracle database. The tables of a database hold all of the user accessible data. Table data is stored in rows and columns.

11. What is an Oracle view?
A view is a virtual table. Every view has a query attached to it. (The query is a SELECT statement that identifies the columns and rows of the table(s) the view
uses.)

11. What is Partial Backup?
A Partial Backup is any operating system backup short of a full backup, taken while the database is open or shut down.

12. What is mirrored on-line Redo Log?
A mirrored on-line redo log consists of copies of on-line redo log files physically located on separate disks, changes made to one member of the group are made to all members.

13. What is Full Backup?
A full backup is an operating system backup of all data files, on-line redo log files and control file that constitute ORACLE database and the parameter.

14. Can a View based on another View?
Yes.

15. Can a Tablespace hold objects from different Schemes?
Yes
.
16. Can objects of the same Schema reside in different tablespaces?
Yes.

17. What is the use of Control File?
When an instance of an ORACLE database is started, its control file is used to identify the database and redo log files that must be opened for database operation to proceed. It is also used in database recovery.

18. Do View contain Data?
Views do not contain or store data.

19. What are the Referential actions supported by FOREIGN KEY integrity constraint?
UPDATE and DELETE Restrict – A referential integrity rule that disallows the update or deletion of referenced data. DELETE Cascade – When a referenced row is deleted all associated dependent rows are deleted.

20. What are the types of Synonyms?
There are two types of Synonyms Private and Public.

21. What is a Redo Log?
The set of Redo Log files YSDATE, UID, USER or USERENV SQL functions, or the pseudo columns LEVEL or ROWNUM.

22. What is an Index Segment?
Each Index has an Index segment that stores all of its data.

23. Explain the relationship among Database, Tablespace and Data file.?
Each databases logically divided into one or more tablespaces one or more data
files are explicitly created for each tablespace

24. What are the different types of Segments?
Data Segment, Index Segment, Rollback Segment and Temporary Segment.

25. What are Clusters?
Clusters are groups of one or more tables physically stores together to share common columns and are often used together.

26. What is an Integrity Constraints?
An integrity constraint is a declarative way to define a business rule for a column of a table.

27. What is an Index?
An Index is an optional structure associated with a table to have direct access to rows, which can be created to increase the performance of data retrieval. Index can be created on one or more columns of a table.

28. What is an Extent?
An Extent is a specific number of contiguous data blocks, obtained in a single allocation, and used to store a specific type of information.

29. What is a View?
A view is a virtual table. Every view has a Query attached to it. (The Query is a SELECT statement that identifies the columns and rows of the table(s) the view uses.)

30. What is Table?
A table is the basic unit of data storage in an ORACLE database. The tables of a database hold all of the user accessible data. Table data is stored in rows and columns

31. Can a view based on another view?
Yes.

32. What are the advantages of views?
– Provide an additional level of table security, by restricting access to a predetermined set of rows and columns of a table.
– Hide data complexity.
– Simplify commands for the user.
– Present the data in a different perspective from that of the base table.
– Store complex queries.

33. What is an Oracle sequence?
A sequence generates a serial list of unique numbers for numerical columns of a database’s tables.

34. What is a synonym?
A synonym is an alias for a table, view, sequence or program unit.

35. What are the types of synonyms?
There are two types of synonyms private and public.

36. What is a private synonym?
Only its owner can access a private synonym.

37. What is a public synonym?
Any database user can access a public synonym.

38. What are synonyms used for?
– Mask the real name and owner of an object.
– Provide public access to an object
– Provide location transparency for tables, views or program units of a remote database.
– Simplify the SQL statements for database users.

39. What is an Oracle index?
An index is an optional structure associated with a table to have direct access to rows, which can be created to increase the performance of data retrieval. Index can be created on one or more columns of a table.

40. How are the index updates?
Indexes are automatically maintained and used by Oracle. Changes to table data are automatically incorporated into all relevant indexes.

41. What is a Tablespace?
A database is divided into Logical Storage Unit called tablespaces. A tablespace is used to grouped related logical structures together

42. What is Rollback Segment?
A Database contains one or more Rollback Segments to temporarily store “undo” information.

43. What are the Characteristics of Data Files ?
A data file can be associated with only one database. Once created a data file can’t change size. One or more data files form a logical unit of database storage called a tablespace.

44. How to define Data Block size ?
A data block size is specified for each ORACLE database when the database is created. A database users and allocated free database space in ORACLE datablocks. Block size is specified in INIT.ORA file and can’t be changed latter.

45. What does a Control file Contain ?
A Control file records the physical structure of the database. It contains the
following information.
Database Name
Names and locations of a database’s files and redolog files.
Time stamp of database creation.

46.What is difference between UNIQUE constraint and PRIMARY KEY
constraint ?

A column defined as UNIQUE can contain Nulls while a column defined as PRIMARY KEY can’t contain Nulls.

47.What is Index Cluster ?
A Cluster with an index on the Cluster Key

48.When does a Transaction end ?
When it is committed or Rollbacked.

49. What is the effect of setting the value “ALL_ROWS” for OPTIMIZER_GOAL parameter of the ALTER SESSION command ? What arethe factors that affect OPTIMIZER in choosing an Optimization approach ?
The OPTIMIZER_MODE initialization parameter Statistics in the Data Dictionary the OPTIMIZER_GOAL parameter of the ALTER SESSION command hints in the statement.

50. What is the effect of setting the value “CHOOSE” for OPTIMIZER_GOAL,parameter of the ALTER SESSION Command ?
The Optimizer chooses Cost_based approach and optimizes with the goal of best
throughput if statistics for atleast one of the tables accessed by the SQL
statement exist in the data dictionary. Otherwise the OPTIMIZER chooses
RULE_based approach.

51. How does one create a new database? (for DBA)
One can create and modify Oracle databases using the Oracle “dbca” (Database Configuration Assistant) utility. The dbca utility is located in the $ORACLE_HOME/bin directory. The Oracle Universal Installer (oui) normally starts it after installing the database server software.
One can also create databases manually using scripts. This option, however, is
falling out of fashion, as it is quite involved and error prone. Look at this example
for creating and Oracle 9i database:
CONNECT SYS AS SYSDBA
ALTER SYSTEM SET DB_CREATE_FILE_DEST=’/u01/oradata/’;
ALTER SYSTEM SET DB_CREATE_ONLINE_LOG_DEST_1=’/u02/oradata/’;
ALTER SYSTEM SET DB_CREATE_ONLINE_LOG_DEST_2=’/u03/oradata/’;
CREATE DATABASE;

52. What database block size should I use? (for DBA)
Oracle recommends that your database block size match, or be multiples of your operating system block size. One can use smaller block sizes, but the performance cost is significant. Your choice should depend on the type of application you are running. If you have many small transactions as with OLTP,
use a smaller block size. With fewer but larger transactions, as with a DSS application, use a larger block size. If you are using a volume manager, consider your “operating system block size” to be 8K. This is because volume manager products use 8K blocks (and this is not configurable).
53. What are the different approaches used by Optimizer in choosing an execution plan ?
Rule-based and Cost-based.

54. What does ROLLBACK do ?
ROLLBACK retracts any of the changes resulting from the SQL statements in the
transaction.
How does one coalesce free space?(for DBA)
SMON coalesces free space (extents) into larger, contiguous extents every 2 hours and even then, only for a short period of time.
SMON will not coalesce free space if a tablespace’s default storage parameter “pctincrease” is set to 0. With Oracle 7.3 one can manually coalesce a
tablespace using the ALTER TABLESPACE … COALESCE; command, until then
use:
SQL> alter session set events ‘immediate trace name coalesce level n’;
Where ‘n’ is the tablespace number you get from SELECT TS#, NAME FROM
SYS.TS$;
You can get status information about this process by selecting from the
SYS.DBA_FREE_SPACE_COALESCED dictionary view.

55. How does one prevent tablespace fragmentation? (for DBA)
Always set PCTINCREASE to 0 or 100.
Bizarre values for PCTINCREASE will contribute to fragmentation. For example if you set PCTINCREASE to 1 you will see that your extents are going to have weird and wacky sizes: 100K, 100K, 101K, 102K, etc. Such extents of bizarre size are rarely re-used in their entirety. PCTINCREASE of 0 or 100 gives you nice round extent sizes that can easily be reused. Eg. 100K, 100K, 200K, 400K,
etc.

Use the same extent size for all the segments in a given tablespace. Locally Managed tablespaces (available from 8i onwards) with uniform extent sizes virtually eliminates any tablespace fragmentation. Note that the number of extents per segment does not cause any performance issue anymore, unless
they run into thousands and thousands where additional I/O may be required to fetch the additional blocks where extent maps of the segment are stored.

56. Where can one find the high water mark for a table? (for DBA)
There is no single system table, which contains the high water mark (HWM) for a table. A table’s HWM can be calculated using the results from the following SQL statements:
SELECT BLOCKS
FROM DBA_SEGMENTS
WHERE OWNER=UPPER(owner) AND SEGMENT_NAME = UPPER(table);
ANALYZE TABLE owner.table ESTIMATE STATISTICS;
SELECT EMPTY_BLOCKS
FROM DBA_TABLES
WHERE OWNER=UPPER(owner) AND SEGMENT_NAME = UPPER(table);
Thus, the tables’ HWM = (query result 1) – (query result 2) – 1
NOTE: You can also use the DBMS_SPACE package and calculate the HWM =
TOTAL_BLOCKS – UNUSED_BLOCKS – 1.

57. What is COST-based approach to optimization ?
Considering available access paths and determining the most efficient execution plan based on statistics in the data dictionary for the tables accessed by the statement and their associated clusters and indexes.

58. What does COMMIT do ?
COMMIT makes permanent the changes resulting from all SQL statements in the transaction. The changes made by the SQL statements of a transaction become visible to other user sessions transactions that start only after transaction is committed.

59. How are extents allocated to a segment? (for DBA)
Oracle8 and above rounds off extents to a multiple of 5 blocks when more than 5
blocks are requested. If one requests 16K or 2 blocks (assuming a 8K block
size), Oracle doesn’t round it up to 5 blocks, but it allocates 2 blocks or 16K as
requested. If one asks for 8 blocks, Oracle will round it up to 10 blocks.
Space allocation also depends upon the size of contiguous free space available.
If one asks for 8 blocks and Oracle finds a contiguous free space that is exactly 8
blocks, it would give it you. If it were 9 blocks, Oracle would also give it to you.
Clearly Oracle doesn’t always round extents to a multiple of 5 blocks.
The exception to this rule is locally managed tablespaces. If a tablespace is
created with local extent management and the extent size is 64K, then Oracle
allocates 64K or 8 blocks assuming 8K-block size. Oracle doesn’t round it up to
the multiple of 5 when a tablespace is locally managed.

60. Can one rename a database user (schema)? (for DBA)
No, this is listed as Enhancement Request 158508. Workaround:
Do a user-level export of user A
create new user B
Import system/manager fromuser=A touser=B
Drop user A

61. Define Transaction ?
A Transaction is a logical unit of work that comprises one or more SQL
statements executed by a single user.

62. What is Read-Only Transaction ?
A Read-Only transaction ensures that the results of each query executed in the
transaction are consistant with respect to the same point in time.

63. What is a deadlock ?
Two processes wating to update the rows of a table which are locked by the other process then deadlock arises. In a database environment this will often happen because of not issuing proper row lock commands. Poor design of frontend application may cause this situation and the performance of server will
reduce drastically.
These locks will be released automatically when a commit/rollback operation performed or any one of this processes being killed externally.

64. What is a Schema ?
The set of objects owned by user account is called the schema.

65. What is a cluster Key ?
The related columns of the tables are called the cluster key. The cluster key is indexed using a cluster index and its value is stored only once for multiple tables in the cluster.

66. What is Parallel Server ?
Multiple instances accessing the same database (Only In Multi-CPU environments)

67. What are the basic element of Base configuration of an oracle Database?
It consists of
one or more data files.
one or more control files.
two or more redo log files.
The Database contains
multiple users/schemas
one or more rollback segments
one or more tablespaces
Data dictionary tables
User objects (table,indexes,views etc.,)
The server that access the database consists of SGA (Database buffer, Dictionary Cache Buffers, Redo log buffers, Shared SQL pool)
SMON (System MONito)
PMON (Process MONitor)
LGWR (LoG Write)
DBWR (Data Base Write)
ARCH (ARCHiver)
CKPT (Check Point)
RECO
Dispatcher
User Process with associated PGS

68. What is clusters ?
Group of tables physically stored together because they share common columns and are often used together is called Cluster.

69. What is an Index ? How it is implemented in Oracle Database ?
An index is a database structure used by the server to have direct access of a row in a table. An index is automatically created when a unique of primary key constraint clause is specified in create table comman (Ver 7.0)

70. What is a Database instance ?
A database instance (Server) is a set of memory structure and background processes that access a set of database files.
The process can be shared by all users. The memory structure that are used to store most queried data from database. This helps up to improve database performance by decreasing the amount of I/O performed against data file.

71. WWhat is the use of ANALYZE command ?
To perform one of these function on an index,table, or cluster:
– To collect statistics about object used by the optimizer and store them in the data dictionary.
– To delete statistics about the object used by object from the data dictionary.
– To validate the structure of the object.
– To identify migrated and chained rows of the table or cluster.

72. What is default tablespace ?
The Tablespace to contain schema objects created without specifying a tablespace name.

73. What are the system resources that can be controlled through Profile ?
The number of concurrent sessions the user can establish the CPU processing
time available to the user’s session the CPU processing time available to a single
call to ORACLE made by a SQL statement the amount of logical I/O available to
the user’s session the amout of logical I/O available to a single call to ORACLE
made by a SQL statement the allowed amount of idle time for the user’s session
the allowed amount of connect time for the user’s session.

74. What is Tablespace Quota ?
The collective amount of disk space available to the objects in a schema on a
particular tablespace.

76. What are the different Levels of Auditing ?
Statement Auditing, Privilege Auditing and Object Auditing.

77. What is Statement Auditing ?
Statement auditing is the auditing of the powerful system privileges without
regard to specifically named objects.

78. What are the database administrators utilities avaliable ?
SQL * DBA – This allows DBA to monitor and control an ORACLE database. SQL
* Loader – It loads data from standard operating system files (Flat files) into
ORACLE database tables. Export (EXP) and Import (imp) utilities allow you to
move existing data in ORACLE format to and from ORACLE database.

79. How can you enable automatic archiving ?
Shut the database
Backup the database
Modify/Include LOG_ARCHIVE_START_TRUE in init.ora file.
Start up the database.

80. What are roles? How can we implement roles ?
Roles are the easiest way to grant and manage common privileges needed by
different groups of database users. Creating roles and assigning provides to
roles. Assign each role to group of users. This will simplify the job of assigning
privileges to individual users.

81. What are Roles ?
Roles are named groups of related privileges that are granted to users or other
roles.

82. What are the use of Roles ?
REDUCED GRANTING OF PRIVILEGES – Rather than explicitly granting the
same set of privileges to many users a database administrator can grant the
privileges for a group of related users granted to a role and then grant only the
role to each member of the group.
DYNAMIC PRIVILEGE MANAGEMENT – When the privileges of a group must
change, only the privileges of the role need to be modified. The security domains
of all users granted the group’s role automatically reflect the changes made to
the role.
SELECTIVE AVAILABILITY OF PRIVILEGES – The roles granted to a user can
be selectively enable (available for use) or disabled (not available for use). This
allows specific control of a user’s privileges in any given situation.
APPLICATION AWARENESS – A database application can be designed to
automatically enable and disable selective roles when a user attempts to use the
application.

83. What is Privilege Auditing ?
Privilege auditing is the auditing of the use of powerful system privileges without
regard to specifically named objects.

84. What is Object Auditing ?
Object auditing is the auditing of accesses to specific schema objects without
regard to user.

85. What is Auditing ?
Monitoring of user access to aid in the investigation of database use.

85. How does one see the uptime for a database?
(for DBA
Look at the following SQL query:
SELECT to_char (startup_time,’DD-MON-YYYY HH24: MI: SS’) “DB Startup
Time”
FROM sys.v_$instance;
Marco Bergman provided the following alternative solution:
SELECT to_char (logon_time,’Dy dd Mon HH24: MI: SS’) “DB Startup Time”
FROM sys.v_$session
WHERE Sid=1 /* this is pmon */
/
Users still running on Oracle 7 can try one of the following queries:
Column STARTED format a18 head ‘STARTUP TIME’
Select C.INSTANCE,
to_date (JUL.VALUE, ‘J’)
|| to_char (floor (SEC.VALUE/3600), ’09’)
|| ‘:’
— || Substr (to_char (mod (SEC.VALUE/60, 60), ’09’), 2, 2)
|| Substr (to_char (floor (mod (SEC.VALUE/60, 60)), ’09’), 2, 2)
|| ‘.’
|| Substr (to_char (mod (SEC.VALUE, 60), ’09’), 2, 2) STARTED
from SYS.V_$INSTANCE JUL,
SYS.V_$INSTANCE SEC,
SYS.V_$THREAD C
Where JUL.KEY like ‘%JULIAN%’
and SEC.KEY like ‘%SECOND%’;
Select to_date (JUL.VALUE, ‘J’)
|| to_char (to_date (SEC.VALUE, ‘SSSSS’), ‘ HH24:MI:SS’) STARTED
from SYS.V_$INSTANCE JUL,
SYS.V_$INSTANCE SEC
where JUL.KEY like ‘%JULIAN%’
and SEC.KEY like ‘%SECOND%’;
select to_char (to_date (JUL.VALUE, ‘J’) + (SEC.VALUE/86400), -Return a DATE
‘DD-MON-YY HH24:MI:SS’) STARTED
from V$INSTANCE JUL,
V$INSTANCE SEC
where JUL.KEY like ‘%JULIAN%’
and SEC.KEY like ‘%SECOND%’;

86. Where are my TEMPFILES, I don’t see them in V$DATAFILE or
DBA_DATA_FILE? (for DBA
Tempfiles, unlike normal datafiles, are not listed in v$datafile or dba_data_files.
Instead query v$tempfile or dba_temp_files:
SELECT * FROM v$tempfile;
SELECT * FROM dba_temp_files;

87. How do I find used/free space in a TEMPORARY tablespace?
(for DBA Unlike normal tablespaces, true temporary tablespace information is not listed in
DBA_FREE_SPACE. Instead use the V$TEMP_SPACE_HEADER view:
SELECT tablespace_name, SUM (bytes used), SUM (bytes free)
FROM V$temp_space_header
GROUP BY tablespace_name;

88. What is a profile ?
Each database user is assigned a Profile that specifies limitations on various system resources available to the user.

89. How will you enforce security using stored procedures?
Don’t grant user access directly to tables within the application. Instead grant the
ability to access the procedures that access the tables. When procedure
executed it will execute the privilege of procedures owner. Users cannot access
tables except via the procedure.

90. How can one see who is using a temporary segment?
(for DBA
For every user using temporary space, there is an entry in SYS.V$_LOCK with
type ‘TS’.
All temporary segments are named ‘ffff.bbbb’ where ‘ffff’ is the file it is in and
‘bbbb’ is first block of the segment. If your temporary tablespace is set to
TEMPORARY, all sorts are done in one large temporary segment. For usage
stats, see SYS.V_$SORT_SEGMENT
From Oracle 8.0, one can just query SYS.v$sort_usage. Look at these examples:
select s.username, u.”USER”, u.tablespace, u.contents, u.extents, u.blocks
from sys.v_$session s, sys.v_$sort_usage u
where s.addr = u.session_addr
/
select s.osuser, s.process, s.username, s.serial#,
Sum (u.blocks)*vp.value/1024 sort_size
from sys.v_$session s, sys.v_$sort_usage u, sys.v_$parameter VP
where s.saddr = u.session_addr
and vp.name = ‘db_block_size’
and s.osuser like ‘&1′
group by s.osuser, s.process, s.username, s.serial#, vp.value
/

91. How does one get the view definition of fixed views/tables?
Query v$fixed_view_definition. Example: SELECT * FROM v$fixed_view_definition WHERE view_name=’V$SESSION’;

92. What are the dictionary tables used to monitor a database spaces ?
DBA_FREE_SPACE
DBA_SEGMENTS
DBA_DATA_FILES.

93. How can we specify the Archived log file name format and destination?
By setting the following values in init.ora file. LOG_ARCHIVE_FORMAT = arch
%S/s/T/tarc (%S – Log sequence number and is zero left paded, %s – Log sequence number not padded. %T – Thread number lef-zero-paded and %t – Thread number not padded). The file name created is arch 0001 are if %S is used. LOG_ARCHIVE_DEST = path.

94. What is user Account in Oracle database?
An user account is not a physical structure in Database but it is having important
relationship to the objects in the database and will be having certain privileges.

95. When will the data in the snapshot log be used?
We must be able to create a after row trigger on table (i.e., it should be not be already available) After giving table privileges. We cannot specify snapshot log name because oracle uses the name of the master table in the name of the database objects that support its snapshot log. The master table name should be
less than or equal to 23 characters. (The table name created will be MLOGS_tablename, and trigger name will be TLOGS name).

96. What dynamic data replication?
Updating or Inserting records in remote database through database triggers. It may fail if remote database is having any problem.

97. What is Two-Phase Commit ?
Two-phase commit is mechanism that guarantees a distributed transaction either commits on all involved nodes or rolls back on all involved nodes to maintain data consistency across the global distributed database. It has two phase, a Prepare Phase and a Commit Phase.

98. How can you Enforce Referential Integrity in snapshots ?
Time the references to occur when master tables are not in use. Peform the reference the manually immdiately locking the master tables. We can join tables in snopshots by creating a complex snapshots that will based on the master tables.

99. What is a SQL * NET?
SQL *NET is ORACLE’s mechanism for interfacing with the communication protocols used by the networks that facilitate distributed processing and distributed databases. It is used in Clint-Server and Server-Server communications.

100. What is a SNAPSHOT ?
Snapshots are read-only copies of a master table located on a remote node which is periodically refreshed to reflect changes made to the master table.

101. What is the mechanism provided by ORACLE for table replication ?
Snapshots and SNAPSHOT LOGs

102. What is snapshots?
Snapshot is an object used to dynamically replicate data between distribute database at specified time intervals. In ver 7.0 they are read only.

103. What are the various type of snapshots?
Simple and Complex.

104. Describe two phases of Two-phase commit ?
Prepare phase – The global coordinator (initiating node) ask a participants to prepare (to promise to commit or rollback the transaction, even if there is a failure) Commit – Phase – If all participants respond to the coordinator that they are prepared, the coordinator asks all nodes to commit the transaction, if all
participants cannot prepare, the coordinator asks all nodes to roll back the transaction.

105. What is snapshot log ?
It is a table that maintains a record of modifications to the master table in a snapshot. It is stored in the same database as master table and is only available for simple snapshots. It should be created before creating snapshots.

106. What are the benefits of distributed options in databases?
Database on other servers can be updated and those transactions can be grouped together with others in a logical unit.
Database uses a two phase commit.

107. What are the options available to refresh snapshots ?
COMPLETE – Tables are completely regenerated using the snapshots query and the master tables every time the snapshot referenced.
FAST – If simple snapshot used then a snapshot log can be used to send the changes to the snapshot tables.
FORCE – Default value. If possible it performs a FAST refresh; Otherwise it will perform a complete refresh.

108. What is a SNAPSHOT LOG ?
A snapshot log is a table in the master database that is associated with the master table. ORACLE uses a snapshot log to track the rows that have been updated in the master table. Snapshot logs are used in updating the snapshots based on the master table.

109. What is Distributed database ?
A distributed database is a network of databases managed by multiple database servers that appears to a user as single logical database. The data of all databases in the distributed database can be simultaneously accessed and modified.

110. How can we reduce the network traffic?
– Replication of data in distributed environment.
– Using snapshots to replicate data.
– Using remote procedure calls.

111. Differentiate simple and complex, snapshots ?
– A simple snapshot is based on a query that does not contains GROUP BY
clauses, CONNECT BY clauses, JOINs, sub-query or snashot of operations.
– A complex snapshots contain atleast any one of the above.

112. What are the Built-ins used for sending Parameters to forms?
You can pass parameter values to a form when an application executes the call_form, New_form, Open_form or Run_product.

113. Can you have more than one content canvas view attached with a window?
Yes. Each window you create must have atleast one content canvas view assigned to it. You can also create a window that has manipulated content canvas view. At run time only one of the content canvas views assign to a window is displayed at a time.

114. Is the After report trigger fired if the report execution fails?
Yes.

115. Does a Before form trigger fire when the parameter form is suppressed?
Yes.

116. What is SGA?
The System Global Area in an Oracle database is the area in memory to facilitate the transfer of information between users. It holds the most recently requested structural information between users. It holds the most recently requested structural information about the database. The structure is database buffers,
dictionary cache, redo log buffer and shared pool area.

117. What is a shared pool?
The data dictionary cache is stored in an area in SGA called the shared pool.
This will allow sharing of parsed SQL statements among concurrent users.

118. What is mean by Program Global Area (PGA)?
It is area in memory that is used by a single Oracle user process.

119. What is a data segment?
Data segment are the physical areas within a database block in which the data associated with tables and clusters are stored.

120. What are the factors causing the reparsing of SQL statements in SGA?
Due to insufficient shared pool size.
Monitor the ratio of the reloads takes place while executing SQL statements. If the ratio is greater than 1 then increase the SHARED_POOL_SIZE.

121. What are clusters?
Clusters are groups of one or more tables physically stores together to share common columns and are often used together.

122. What is cluster key?
The related columns of the tables in a cluster are called the cluster key.

123. Do a view contain data?
Views do not contain or store data.

124. What is user Account in Oracle database?
A user account is not a physical structure in database but it is having important relationship to the objects in the database and will be having certain privileges.

125. How will you enforce security using stored procedures?
Don’t grant user access directly to tables within the application. Instead grant the ability to access the procedures that access the tables. When procedure executed it will execute the privilege of procedures owner. Users cannot access tables except via the procedure.

126. What are the dictionary tables used to monitor a database space?
DBA_FREE_SPACE
DBA_SEGMENTS
DBA_DATA_FILES.

127. Can a property clause itself be based on a property clause?
Yes

128. If a parameter is used in a query without being previously defined,what diff. exist betw. report 2.0 and 2.5 when the query is applied?
While both reports 2.0 and 2.5 create the parameter, report 2.5 gives a message that a bind parameter has been created.

129. What are the sql clauses supported in the link property sheet?
Where start with having.

130. What is trigger associated with the timer?
When-timer-expired.

131. What are the trigger associated with image items?
When-image-activated fires when the operators double clicks on an image itemwhen-image-pressed fires when an operator clicks or double clicks on an image item

132. What are the different windows events activated at runtimes?
When_window_activated
When_window_closed
When_window_deactivated
When_window_resized
Within this triggers, you can examine the built in system variable system.
event_window to determine the name of the window for which the trigger fired.

133. When do you use data parameter type?
When the value of a data parameter being passed to a called product is always the name of the record group defined in the current form. Data parameters are used to pass data to produts invoked with the run_product built-in subprogram.

134. What is difference between open_form and call_form?
when one form invokes another form by executing open_form the first form remains displayed, and operators can navigate between the forms as desired. when one form invokes another form by executing call_form, the called form is modal with respect to the calling form. That is, any windows that belong to the
calling form are disabled, and operators cannot navigate to them until they first exit the called form.

135. What is new_form built-in?
When one form invokes another form by executing new_form oracle form exits the first form and releases its memory before loading the new form calling new form completely replace the first with the second. If there are changes pending in the first form, the operator will be prompted to save them before the new form is
loaded.

136. What is the “LOV of Validation” Property of an item? What is the use of it?
When LOV for Validation is set to True, Oracle Forms compares the current value of the text item to the values in the first column displayed in the LOV. Whenever the validation event occurs. If the value in the text item matches one of the values in the first column of the LOV, validation succeeds, the LOV is not
displayed, and processing continues normally. If the value in the text item does not match one of the values in the first column of the LOV, Oracle Forms displays the LOV and uses the text item value as the search criteria to automatically reduce the list

137. What is the diff. when Flex mode is mode on and when it is off?
When flex mode is on, reports automatically resizes the parent when the child is resized.

138. What is the diff. when confine mode is on and when it is off?
When confine mode is on, an object cannot be moved outside its parent in the layout.

139. What are visual attributes?
Visual attributes are the font, color, pattern proprieties that you set for form and
menu objects that appear in your application interface.

140. Which of the two views should objects according to possession?
view by structure.

141. What are the two types of views available in the object navigator?
View by structure and view by type .

142. What are the vbx controls?
Vbx control provide a simple method of building and enhancing user interfaces.
The controls can use to obtain user inputs and display program outputs.vbx control where originally develop as extensions for the ms visual basic environments and include such items as sliders, rides and knobs.

143. What is the use of transactional triggers?
Using transactional triggers we can control or modify the default functionality of the oracle forms.

144. How do you create a new session while open a new form?
Using open_form built-in setting the session option Ex. Open_form(‘Stocks’,active,session). when invoke the mulitiple forms with open form and call_form in the same application, state whether the following are true/False

145. What are the ways to monitor the performance of the report?
Use reports profile executable statement. Use SQL trace facility.

146. If two groups are not linked in the data model editor, What is the hierarchy between them?
Two group that is above are the left most rank higher than the group that is to right or below it.

147. An open form can not be execute the call_form procedure if you chain of called forms has been initiated by another open form?
True

148. Explain about horizontal, Vertical tool bar canvas views?
Tool bar canvas views are used to create tool bars for individual windows. Horizontal tool bars are display at the top of a window, just under its menu bar.
Vertical Tool bars are displayed along the left side of a window

149. What is the purpose of the product order option in the column property sheet?
To specify the order of individual group evaluation in a cross products.

150. What is the use of image_zoom built-in?
To manipulate images in image items.

151. How do you reference a parameter indirectly?
To indirectly reference a parameter use the NAME IN, COPY ‘built-ins to indirectly set and reference the parameters value’ Example name_in (‘capital parameter my param’), Copy (‘SURESH’,’Parameter my_param’)

152. What is a timer?
Timer is an “internal time clock” that you can programmatically create to perform an action each time the times.

153. What are the two phases of block coordination?
There are two phases of block coordination: the clear phase and the population phase. During, the clear phase, Oracle Forms navigates internally to the detail block and flushes the obsolete detail records. During the population phase, Oracle Forms issues a SELECT statement to repopulate the detail block with
detail records associated with the new master record. These operations are accomplished through the execution of triggers.

154. What are Most Common types of Complex master-detail relationships?
There are three most common types of complex master-detail relationships:
master with dependent details
master with independent details
detail with two masters

155. What is a text list?
The text list style list item appears as a rectangular box which displays the fixed
number of values. When the text list contains values that can not be displayed, a
vertical scroll bar appears, allowing the operator to view and select undisplayed
values.

156. What is term?
The term is terminal definition file that describes the terminal form which you are using r20run

167. How does one do off-line database backups?
(for DBA
Shut down the database from sqlplus or server manager. Backup all files to
secondary storage (eg. tapes). Ensure that you backup all data files, all control
files and all log files. When completed, restart your database.
Do the following queries to get a list of all files that needs to be backed up:
select name from sys.v_$datafile;
select member from sys.v_$logfile;
select name from sys.v_$controlfile;
Sometimes Oracle takes forever to shutdown with the “immediate” option. As
workaround to this problem, shutdown using these commands:
alter system checkpoint;
shutdown abort
startup restrict
shutdown immediate
Note that if you database is in ARCHIVELOG mode, one can still use archived
log files to roll forward from an off-line backup. If you cannot take your database
down for a cold (off-line) backup at a convenient time, switch your database into
ARCHIVELOG mode and perform hot (on-line) backups.

170. How does one do on-line database backups? (for DBA
Each tablespace that needs to be backed-up must be switched into backup mode
before copying the files out to secondary storage (tapes). Look at this simple
example.
ALTER TABLESPACE xyz BEGIN BACKUP;
! cp xyfFile1 /backupDir/
ALTER TABLESPACE xyz END BACKUP;
It is better to backup tablespace for tablespace than to put all tablespaces in
backup mode. Backing them up separately incurs less overhead. When done,
remember to backup your control files. Look at this example:
ALTER SYSTEM SWITCH LOGFILE; — Force log switch to update control file
headers
ALTER DATABASE BACKUP CONTROLFILE TO ‘/backupDir/control.dbf’;
NOTE: Do not run on-line backups during peak processing periods. Oracle will
write complete database blocks instead of the normal deltas to redo log files
while in backup mode. This will lead to excessive database archiving and even
database freezes.
171. How does one backup a database using RMAN? (for DBA
The biggest advantage of RMAN is that it only backup used space in the
database. Rman doesn’t put tablespaces in backup mode, saving on redo
generation overhead. RMAN will re-read database blocks until it gets a
consistent image of it. Look at this simple backup example.
rman target sys/*** nocatalog
run {
allocate channel t1 type disk;
backup
format ‘/app/oracle/db_backup/%d_t%t_s%s_p%p’
( database );
release channel t1;
}
Example RMAN restore:
rman target sys/*** nocatalog
run {
allocate channel t1 type disk;
# set until time ‘Aug 07 2000 :51’;
restore tablespace users;
recover tablespace users;
release channel t1;
}
The examples above are extremely simplistic and only useful for illustrating basic
concepts. By default Oracle uses the database controlfiles to store information
about backups. Normally one would rather setup a RMAN catalog database to
store RMAN metadata in. Read the Oracle Backup and Recovery Guide before
implementing any RMAN backups.
Note: RMAN cannot write image copies directly to tape. One needs to use a
third-party media manager that integrates with RMAN to backup directly to tape.
Alternatively one can backup to disk and then manually copy the backups to
tape.
172. What are the different file extensions that are created by oracle
reports?
Rep file and Rdf file.
173. What is strip sources generate options?
Removes the source code from the library file and generates a library files that
contains only pcode. The resulting file can be used for final deployment, but can
not be subsequently edited in the designer.ex. f45gen module=old_lib.pll
userid=scott/tiger strip_source YES output_file
173. How does one put a database into ARCHIVELOG mode? (for DBA
The main reason for running in archivelog mode is that one can provide 24-hour
availability and guarantee complete data recoverability. It is also necessary to
enable ARCHIVELOG mode before one can start to use on-line database
backups. To enable ARCHIVELOG mode, simply change your database startup
command script, and bounce the database:
SQLPLUS> connect sys as sysdba
SQLPLUS> startup mount exclusive;
SQLPLUS> alter database archivelog;
SQLPLUS> archive log start;
SQLPLUS> alter database open;
NOTE1: Remember to take a baseline database backup right after enabling
archivelog mode. Without it one would not be able to recover. Also, implement an
archivelog backup to prevent the archive log directory from filling-up.
NOTE2: ARCHIVELOG mode was introduced with Oracle V6, and is essential for
database point-in-time recovery. Archiving can be used in combination with online
and off-line database backups.
NOTE3: You may want to set the following INIT.ORA parameters when enabling
ARCHIVELOG mode: log_archive_start=TRUE, log_archive_dest=… and
log_archive_format=…
NOTE4: You can change the archive log destination of a database on-line with
the ARCHIVE LOG START TO ‘directory’; statement. This statement is often
used to switch archiving between a set of directories.
NOTE5: When running Oracle Real Application Server (RAC), you need to shut
down all nodes before changing the database to ARCHIVELOG mode.
174. What is the basic data structure that is required for creating an LOV?
Record Group.
175. How does one backup archived log files? (for DBA
One can backup archived log files using RMAN or any operating system backup
utility. Remember to delete files after backing them up to prevent the archive log
directory from filling up. If the archive log directory becomes full, your database
will hang! Look at this simple RMAN backup script:
RMAN> run {
2> allocate channel dev1 type disk;
3> backup
4> format ‘/app/oracle/arch_backup/log_t%t_s%s_p%p’
5> (archivelog all delete input);
6> release channel dev1;
7> }
176. Does Oracle write to data files in begin/hot backup mode? (for DBA
Oracle will stop updating file headers, but will continue to write data to the
database files even if a tablespace is in backup mode.
In backup mode, Oracle will write out complete changed blocks to the redo log
files. Normally only deltas (changes) are logged to the redo logs. This is done to
enable reconstruction of a block if only half of it was backed up (split blocks).
Because of this, one should notice increased log activity and archiving during online
backups.
188. What is an administrative (privileged) user? (for DBA
Oracle DBAs and operators typically use administrative accounts to manage the
database and database instance. An administrative account is a user that is
granted SYSOPER or SYSDBA privileges. SYSDBA and SYSOPER allow
access to a database instance even if it is not running. Control of these privileges
is managed outside of the database via password files and special operating
system groups. This password file is created with the orapwd utility.
191. How does one connect to an administrative user? (for DBA
If an administrative user belongs to the “dba” group on Unix, or the “ORA_DBA”
(ORA_sid_DBA) group on NT, he/she can connect like this:
connect / as sysdba
No password is required. This is equivalent to the desupported “connect internal”
method.
A password is required for “non-secure” administrative access. These passwords
are stored in password files. Remote connections via Net8 are classified as nonsecure.
Look at this example:
connect sys/password as sysdba
192. How does one create a password file? (for DBA
The Oracle Password File ($ORACLE_HOME/dbs/orapw or orapwSID) stores
passwords for users with administrative privileges. One needs to create a
password files before remote administrators (like OEM) will be allowed to
connect.
Follow this procedure to create a new password file:
. Log in as the Oracle software owner
. Runcommand: orapwd file=$ORACLE_HOME/dbs/orapw$ORACLE_SID
password=mypasswd
. Shutdown the database (SQLPLUS> SHUTDOWN IMMEDIATE)
. Edit the INIT.ORA file and ensure
REMOTE_LOGIN_PASSWORDFILE=exclusive is set.
. Startup the database (SQLPLUS> STARTUP)
NOTE: The orapwd utility presents a security risk in that it receives a password
from the command line. This password is visible in the process table of many
systems. Administrators needs to be aware of this!
195. How does one add users to a password file? (for DBA
One can select from the SYS.V_$PWFILE_USERS view to see which users are
listed in the password file. New users can be added to the password file by
granting them SYSDBA or SYSOPER privileges, or by using the orapwd utility.
GRANT SYSDBA TO scott;
197. Why are OPS$ accounts a security risk in a client/server environment?
(for DBA
If you allow people to log in with OPS$ accounts from Windows Workstations,
you cannot be sure who they really are. With terminals, you can rely on operating
system passwords, with Windows, you cannot.
If you set REMOTE_OS_AUTHENT=TRUE in your init.ora file, Oracle assumes
that the remote OS has authenticated the user. If REMOTE_OS_AUTHENT is set
to FALSE (recommended), remote users will be unable to connect without a
password. IDENTIFIED EXTERNALLY will only be in effect from the local host.
Also, if you are using “OPS$” as your prefix, you will be able to log on locally with
or without a password, regardless of whether you have identified your ID with a
password or defined it to be IDENTIFIED EXTERNALLY.
236. What third party tools can be used with Oracle EBU/ RMAN? (for DBA
The following Media Management Software Vendors have integrated their media
management software packages with Oracle Recovery Manager and Oracle7
Enterprise Backup Utility. The Media Management Vendors will provide first line
technical support for the integrated backup/recover solutions.
Veritas NetBackup
EMC Data Manager (EDM)
HP OMNIBack II
IBM’s Tivoli Storage Manager – formerly ADSM
Legato Networker
ManageIT Backup and Recovery
Sterling Software’s SAMS:Alexandria – formerly from Spectralogic
Sun Solstice Backup
237. Why and when should one tune? (for DBA
One of the biggest responsibilities of a DBA is to ensure that the Oracle database
is tuned properly. The Oracle RDBMS is highly tunable and allows the database
to be monitored and adjusted to increase its performance. One should do
performance tuning for the following reasons:
The speed of computing might be wasting valuable human time (users waiting for
response); Enable your system to keep-up with the speed business is conducted;
and Optimize hardware usage to save money (companies are spending millions
on hardware). Although this FAQ is not overly concerned with hardware issues,
one needs to remember than you cannot tune a Buick into a Ferrari.
241. What database aspects should be monitored? (for DBA
One should implement a monitoring system to constantly monitor the following
aspects of a database. Writing custom scripts, implementing Oracle’s Enterprise
Manager, or buying a third-party monitoring product can achieve this. If an alarm
is triggered, the system should automatically notify the DBA (e-mail, page, etc.)
to take appropriate action.
Infrastructure availability:
. Is the database up and responding to requests
. Are the listeners up and responding to requests
. Are the Oracle Names and LDAP Servers up and responding to requests
. Are the Web Listeners up and responding to requests
Things that can cause service outages:
. Is the archive log destination filling up?
. Objects getting close to their max extents
. User and process limits reached
Things that can cause bad performance:
See question “What tuning indicators can one use?”.
242. Where should the tuning effort be directed? (for DBA
Consider the following areas for tuning. The order in which steps are listed needs
to be maintained to prevent tuning side effects. For example, it is no good
increasing the buffer cache if you can reduce I/O by rewriting a SQL statement.
Database Design (if it’s not too late):
Poor system performance usually results from a poor database design. One
should generally normalize to the 3NF. Selective denormalization can provide
valuable performance improvements. When designing, always keep the “data
access path” in mind. Also look at proper data partitioning, data replication,
aggregation tables for decision support systems, etc.
Application Tuning:
Experience showed that approximately 80% of all Oracle system performance
problems are resolved by coding optimal SQL. Also consider proper scheduling
of batch tasks after peak working hours.
Memory Tuning:
Properly size your database buffers (shared pool, buffer cache, log buffer, etc) by
looking at your buffer hit ratios. Pin large objects into memory to prevent frequent
reloads.
Disk I/O Tuning:
Database files needs to be properly sized and placed to provide maximum disk
subsystem throughput. Also look for frequent disk sorts, full table scans, missing
indexes, row chaining, data fragmentation, etc
Eliminate Database Contention:
Study database locks, latches and wait events carefully and eliminate where
possible. Tune the Operating System:
Monitor and tune operating system CPU, I/O and memory utilization. For more
information, read the related Oracle FAQ dealing with your specific operating
system.
256. Does one need to drop/ truncate objects before importing? (for DBA
Before one import rows into already populated tables, one needs to truncate or
drop these tables to get rid of the old data. If not, the new data will be appended
to the existing tables. One must always DROP existing Sequences before reimporting.
If the sequences are not dropped, they will generate numbers
inconsistent with the rest of the database. Note: It is also advisable to drop
indexes before importing to speed up the import process. Indexes can easily be
recreated after the data was successfully imported.
258. Can one import/export between different versions of Oracle? (for DBA
Different versions of the import utility is upwards compatible. This means that one
can take an export file created from an old export version, and import it using a
later version of the import utility. This is quite an effective way of upgrading a
database from one release of Oracle to the next.
Oracle also ships some previous catexpX.sql scripts that can be executed as
user SYS enabling older imp/exp versions to work (for backwards compatibility).
For example, one can run $ORACLE_HOME/rdbms/admin/catexp7.sql on an
Oracle 8 database to allow the Oracle 7.3 exp/imp utilities to run against an
Oracle 8 database.
260. Can one export to multiple files?/ Can one beat the Unix 2 Gig limit?
(for DBA
From Oracle8i, the export utility supports multiple output files. This feature
enables large exports to be divided into files whose sizes will not exceed any
operating system limits (FILESIZE= parameter). When importing from multi-file
export you must provide the same filenames in the same sequence in the FILE=
parameter. Look at this example:
exp SCOTT/TIGER FILE=D:\F1.dmp,E:\F2.dmp FILESIZE=10m LOG=scott.log
Use the following technique if you use an Oracle version prior to 8i:
Create a compressed export on the fly. Depending on the type of data, you
probably can export up to 10 gigabytes to a single file. This example uses gzip. It
offers the best compression I know of, but you can also substitute it with zip,
compress or whatever.
# create a named pipe
mknod exp.pipe p
# read the pipe – output to zip file in the background
gzip < exp.pipe > scott.exp.gz &
# feed the pipe
exp userid=scott/tiger file=exp.pipe …
262. How can one improve Import/ Export performance? (for DBA
EXPORT:
. Set the BUFFER parameter to a high value (e.g. 2M)
. Set the RECORDLENGTH parameter to a high value (e.g. 64K)
. Stop unnecessary applications to free-up resources for your job.
. If you run multiple export sessions, ensure they write to different physical disks.
. DO NOT export to an NFS mounted filesystem. It will take forever.
IMPORT:
. Create an indexfile so that you can create indexes AFTER you have imported
data. Do this by setting INDEXFILE to a filename and then import. No data will be
imported but a file containing index definitions will be created. You must edit this
file afterwards and supply the passwords for the schemas on all CONNECT
statements.
. Place the file to be imported on a separate physical disk from the oracle data
files
. Increase DB_CACHE_SIZE (DB_BLOCK_BUFFERS prior to 9i) considerably in
the init$SID.ora file
. Set the LOG_BUFFER to a big value and restart oracle.
. Stop redo log archiving if it is running (ALTER DATABASE NOARCHIVELOG;)
. Create a BIG tablespace with a BIG rollback segment inside. Set all other
rollback segments offline (except the SYSTEM rollback segment of course). The
rollback segment must be as big as your biggest table (I think?)
. Use COMMIT=N in the import parameter file if you can afford it
. Use ANALYZE=N in the import parameter file to avoid time consuming
ANALYZE statements
. Remember to run the indexfile previously created
264. What are the common Import/ Export problems? (for DBA
ORA-00001: Unique constraint (…) violated – You are importing duplicate rows.
Use IGNORE=NO to skip tables that already exist (imp will give an error if the
object is re-created).
ORA-01555: Snapshot too old – Ask your users to STOP working while you are
exporting or use parameter CONSISTENT=NO
ORA-01562: Failed to extend rollback segment – Create bigger rollback
segments or set parameter COMMIT=Y while importing
IMP-00015: Statement failed … object already exists… – Use the IGNORE=Y
import parameter to ignore these errors, but be careful as you might end up with
duplicate rows.
276. My database was terminated while in BACKUP MODE, do I need to
recover? (for DBA
If a database was terminated while one of its tablespaces was in BACKUP
MODE (ALTER TABLESPACE xyz BEGIN BACKUP;), it will tell you that media
recovery is required when you try to restart the database. The DBA is then
required to recover the database and apply all archived logs to the database.
However, from Oracle7.2, you can simply take the individual datafiles out of
backup mode and restart the database.
ALTER DATABASE DATAFILE ‘/path/filename’ END BACKUP;
One can select from V$BACKUP to see which datafiles are in backup mode. This
normally saves a significant amount of database down time.
Thiru Vadivelu contributed the following:
From Oracle9i onwards, the following command can be used to take all of the
datafiles out of hot backup mode:
ALTER DATABASE END BACKUP;
The above commands need to be issued when the database is mounted.
279. My database is down and I cannot restore. What now? (for DBA
Recovery without any backup is normally not supported, however, Oracle
Consulting can sometimes extract data from an offline database using a utility
called DUL (Disk UnLoad). This utility reads data in the data files and unloads it
into SQL*Loader or export dump files. DUL does not care about rollback
segments, corrupted blocks, etc, and can thus not guarantee that the data is not
logically corrupt. It is intended as an absolute last resort and will most likely cost
your company a lot of money!!!
280. I’ve lost my REDOLOG files, how can I get my DB back? (for DBA
The following INIT.ORA parameter may be required if your current redo logs are
corrupted or blown away. Caution is advised when enabling this parameter as
you might end-up losing your entire database. Please contact Oracle Support
before using it. _allow_resetlogs_corruption = true
283. I’ve lost some Rollback Segments, how can I get my DB back? (for
DBA
Re-start your database with the following INIT.ORA parameter if one of your
rollback segments is corrupted. You can then drop the corrupted rollback
segments and create it from scratch.
Caution is advised when enabling this parameter, as uncommitted transactions
will be marked as committed. One can very well end up with lost or inconsistent
data!!! Please contact Oracle Support before using it.
_Corrupted_rollback_segments = (rbs01, rbs01, rbs03, rbs04)
284. What are the differences between EBU and RMAN? (for DBA
Enterprise Backup Utility (EBU) is a functionally rich, high performance interface
for backing up Oracle7 databases. It is sometimes referred to as OEBU for
Oracle Enterprise Backup Utility. The Oracle Recovery Manager (RMAN) utility
that ships with Oracle8 and above is similar to Oracle7’s EBU utility. However,
there is no direct upgrade path from EBU to RMAN.
285. How does one create a RMAN recovery catalog? (for DBA
Start by creating a database schema (usually called rman). Assign an
appropriate tablespace to it and grant it the recovery_catalog_owner role. Look at
this example:
sqlplus sys
SQL>create user rman identified by rman;
SQL> alter user rman default tablespace tools temporary tablespace temp;
SQL> alter user rman quota unlimited on tools;
SQL> grant connect, resource, recovery_catalog_owner to rman;
SQL> exit;
Next, log in to rman and create the catalog schema. Prior to Oracle 8i this was
done by running the catrman.sql script. rman catalog rman/rman
RMAN>create catalog tablespace tools;
RMAN> exit;
You can now continue by registering your databases in the catalog. Look at this
example:
rman catalog rman/rman target backdba/backdba
RMAN> register database;
314. What is the difference between locks, latches, enqueues and
semaphores? (for DBA
A latch is an internal Oracle mechanism used to protect data structures in the
SGA from simultaneous access. Atomic hardware instructions like TEST-ANDSET
is used to implement latches. Latches are more restrictive than locks in that
they are always exclusive. Latches are never queued, but will spin or sleep until
they obtain a resource, or time out.
Enqueues and locks are different names for the same thing. Both support
queuing and concurrency. They are queued and serviced in a first-in-first-out
(FIFO) order.
Semaphores are an operating system facility used to control waiting.
Semaphores are controlled by the following Unix parameters: semmni, semmns
and semmsl. Typical settings are:
semmns = sum of the “processes” parameter for each instance
(see init<instance>.ora for each instance)
semmni = number of instances running simultaneously;
semmsl = semmns
315. What is a logical backup?
Logical backup involves reading a set of database records and writing them into
a file. Export utility is used for taking backup and Import utility is used to recover
from backup.
316. Where can one get a list of all hidden Oracle parameters? (for DBA
Oracle initialization or INIT.ORA parameters with an underscore in front are
hidden or unsupported parameters. One can get a list of all hidden parameters
by executing this query:
select *
from SYS.X$KSPPI
where substr(KSPPINM,1,1) = ‘_’;
The following query displays parameter names with their current value:
select a.ksppinm “Parameter”, b.ksppstvl “Session Value”, c.ksppstvl “Instance
Value”
from x$ksppi a, x$ksppcv b, x$ksppsv c
where a.indx = b.indx and a.indx = c.indx
and substr(ksppinm,1,1)=’_’
order by a.ksppinm;
Remember: Thou shall not play with undocumented parameters!
317. What is a database EVENT and how does one set it? (for DBA
Oracle trace events are useful for debugging the Oracle database server. The
following two examples are simply to demonstrate syntax. Refer to later notes on
this page for an explanation of what these particular events do.
Either adding them to the INIT.ORA parameter file can activate events. E.g.
event=’1401 trace name errorstack, level 12′
… or, by issuing an ALTER SESSION SET EVENTS command: E.g.
alter session set events ‘10046 trace name context forever, level 4’;
The alter session method only affects the user’s current session, whereas
changes to the INIT.ORA file will affect all sessions once the database has been
restarted.
318. What is a Rollback segment entry ?
It is the set of before image data blocks that contain rows that are modified by a
transaction. Each Rollback Segment entry must be completed within one rollback
segment. A single rollback segment can have multiple rollback segment entries.
319. What database events can be set? (for DBA
The following events are frequently used by DBAs and Oracle Support to
diagnose problems:
” 10046 trace name context forever, level 4 Trace SQL statements and show bind
variables in trace output.
” 10046 trace name context forever, level 8 This shows wait events in the SQL
trace files
” 10046 trace name context forever, level 12 This shows both bind variable
names and wait events in the SQL trace files
” 1401 trace name errorstack, level 12 1401 trace name errorstack, level 4 1401
trace name processstate Dumps out trace information if an ORA-1401 “inserted
value too large for column” error occurs. The 1401 can be replaced by any other
Oracle Server error code that you want to trace.
” 60 trace name errorstack level 10 Show where in the code Oracle gets a
deadlock (ORA-60), and may help to diagnose the problem.
The following lists of events are examples only. They might be version specific,
so please call Oracle before using them:
” 10210 trace name context forever, level 10 10211 trace name context forever,
level 10 10231 trace name context forever, level 10 These events prevent
database block corruptions
” 10049 trace name context forever, level 2 Memory protect cursor
” 10210 trace name context forever, level 2 Data block check
” 10211 trace name context forever, level 2 Index block check
” 10235 trace name context forever, level 1 Memory heap check
” 10262 trace name context forever, level 300 Allow 300 bytes memory leak for
connections
Note: You can use the Unix oerr command to get the description of an event. On
Unix, you can type “oerr ora 10053” from the command prompt to get event
details.
320. How can one dump internal database structures? (for DBA
The following (mostly undocumented) commands can be used to obtain
information about internal database structures.
o Dump control file contents
alter session set events ‘immediate trace name CONTROLF level 10’
/
o Dump file headers
alter session set events ‘immediate trace name FILE_HDRS level 10’
/
o Dump redo log headers
alter session set events ‘immediate trace name REDOHDR level 10’
/
o Dump the system state
NOTE: Take 3 successive SYSTEMSTATE dumps, with 10-minute intervals alter
session set events ‘immediate trace name SYSTEMSTATE level 10’
/
o Dump the process state
alter session set events ‘immediate trace name PROCESSSTATE level 10’
/
o Dump Library Cache details
alter session set events ‘immediate trace name library cache level 10’
/
o Dump optimizer statistics whenever a SQL statement is parsed (hint: change
statement or flush pool) alter session set events ‘10053 trace name context
forever, level 1’
/
o Dump a database block (File/ Block must be converted to DBA address)
Convert file and block number to a DBA (database block address).
Eg: variable x varchar2;
exec 😡 := dbms_utility.make_data_block_address(1,12);
print x
alter session set events ‘immediate trace name blockdump level 50360894’
/
321. What are the different kind of export backups?
Full back – Complete database
Incremental – Only affected tables from last incremental date/full backup date.
Cumulative backup – Only affected table from the last cumulative date/full backup
date.
327. How does Space allocation table place within a block ?
Each block contains entries as follows
Fixed block header
Variable block header
Row Header,row date (multiple rows may exists)
PCTEREE (% of free space for row updation in future)
328. What are the factors causing the reparsing of SQL statements in SGA?
Due to insufficient Shared SQL pool size. Monitor the ratio of the reloads takes
place while executing SQL statements. If the ratio is greater than 1 then increase
the SHARED_POOL_SIZE. LOGICAL & PHYSICAL ARCHITECTURE OF
DATABASE.
329. What is dictionary cache ?
Dictionary cache is information about the databse objects stored in a data
dictionary table.
330. What is a Control file ?
Database overall physical architecture is maintained in a file called control file. It
will be used to maintain internal consistency and guide recovery operations.
Multiple copies of control files are advisable.
331. What is Database Buffers ?
Database buffers are cache in the SGA used to hold the data blocks that are
read from the data segments in the database such as tables, indexes and
clusters DB_BLOCK_BUFFERS parameter in INIT.ORA decides the size.
332. How will you create multiple rollback segments in a database ?
Create a database which implicitly creates a SYSTEM Rollback Segment in a
SYSTEM tablespace. Create a Second Rollback Segment name R0 in the
SYSTEM tablespace. Make new rollback segment available (After shutdown,
modify init.ora file and Start database) Create other tablespaces (RBS) for
rollback segments. Deactivate Rollback Segment R0 and activate the newly
created rollback segments.
333. What is cold backup? What are the elements of it?
Cold backup is taking backup of all physical files after normal shutdown of
database. We need to take.
– All Data files.
– All Control files.
– All on-line redo log files.
– The init.ora file (Optional)
334. What is meant by redo log buffer ?
Changes made to entries are written to the on-line redo log files. So that they can
be used in roll forward operations during database recoveries. Before writing
them into the redo log files, they will first brought to redo log buffers in SGA and
LGWR will write into files frequently. LOG_BUFFER parameter will decide the
size.
335. How will you estimate the space required by a non-clustered tables?
Calculate the total header size
Calculate the available dataspace per data block
Calculate the combined column lengths of the average row
Calculate the total average row size.
Calculate the average number rows that can fit in a block
Calculate the number of blocks and bytes required for the table.
After arriving the calculation, add 10 % additional space to calculate the initial
extent size for a working table.
336. How will you monitor the space allocation ?
By querying DBA_SEGMENT table/view.
337. What is meant by free extent ?
A free extent is a collection of continuous free blocks in tablespace. When a
segment is dropped its extents are reallocated and are marked as free.
349. What are the different methods of backing up oracle database ?
– Logical Backups
– Cold Backups
– Hot Backups (Archive log)
358. What is an SQL *FORMS ?
SQL *forms is 4GL tool for developing and executing; Oracle based interactive
application.
381. When is cost based optimization triggered? (for DBA
It’s important to have statistics on all tables for the CBO (Cost Based Optimizer)
to work correctly. If one table involved in a statement does not have statistics,
Oracle has to revert to rule-based optimization for that statement. So you really
want for all tables to have statistics right away; it won’t help much to just have the
larger tables analyzed.
Generally, the CBO can change the execution plan when you:
1. Change statistics of objects by doing an ANALYZE;
2. Change some initialization parameters (for example: hash_join_enabled,
sort_area_size, db_file_multiblock_read_count).
382. How can one optimize %XYZ% queries? (for DBA
It is possible to improve %XYZ% queries by forcing the optimizer to scan all the
entries from the index instead of the table. This can be done by specifying hints.
If the index is physically smaller than the table (which is usually the case) it will
take less time to scan the entire index than to scan the entire table.
384. Where can one find I/O statistics per table? (for DBA
The UTLESTAT report shows I/O per tablespace but one cannot see what tables
in the tablespace has the most I/O. The $ORACLE_HOME/rdbms/admin/catio.sql
script creates a sample_io procedure and table to gather the required
information. After executing the procedure, one can do a simple SELECT *
FROM io_per_object; to extract the required information. For more details, look
at the header comments in the $ORACLE_HOME/rdbms/admin/catio.sql script.
385. My query was fine last week and now it is slow. Why? (for DBA
The likely cause of this is because the execution plan has changed. Generate a
current explain plan of the offending query and compare it to a previous one that
was taken when the query was performing well. Usually the previous plan is not
available.
Some factors that can cause a plan to change are:
. Which tables are currently analyzed? Were they previously analyzed? (ie. Was
the query using RBO and now CBO?)
. Has OPTIMIZER_MODE been changed in INIT.ORA?
. Has the DEGREE of parallelism been defined/changed on any table?
. Have the tables been re-analyzed? Were the tables analyzed using estimate or
compute? If estimate, what percentage was used?
. Have the statistics changed?
. Has the INIT.ORA parameter DB_FILE_MULTIBLOCK_READ_COUNT been
changed?
. Has the INIT.ORA parameter SORT_AREA_SIZE been changed?
. Have any other INIT.ORA parameters been changed?
. What do you think the plan should be? Run the query with hints to see if this
produces the required performance.
386. Why is Oracle not using the damn index? (for DBA
This problem normally only arises when the query plan is being generated by the
Cost Based Optimizer. The usual cause is because the CBO calculates that
executing a Full Table Scan would be faster than accessing the table via the
index.
Fundamental things that can be checked are:
. USER_TAB_COLUMNS.NUM_DISTINCT – This column defines the number of
distinct values the column holds.
. USER_TABLES.NUM_ROWS – If NUM_DISTINCT = NUM_ROWS then using
an index would be preferable to doing a FULL TABLE SCAN. As the
NUM_DISTINCT decreases, the cost of using an index increase thereby is
making the index less desirable.
. USER_INDEXES.CLUSTERING_FACTOR – This defines how ordered the rows
are in the index. If CLUSTERING_FACTOR approaches the number of blocks in
the table, the rows are ordered. If it approaches the number of rows in the table,
the rows are randomly ordered. In such a case, it is unlikely that index entries in
the same leaf block will point to rows in the same data blocks.
. Decrease the INIT.ORA parameter DB_FILE_MULTIBLOCK_READ_COUNT – A
higher value will make the cost of a FULL TABLE SCAN cheaper.
. Remember that you MUST supply the leading column of an index, for the index
to be used (unless you use a FAST FULL SCAN or SKIP SCANNING).
. There are many other factors that affect the cost, but sometimes the above can
help to show why an index is not being used by the CBO. If from checking the
above you still feel that the query should be using an index, try specifying an
index hint. Obtain an explain plan of the query either using TKPROF with
TIMED_STATISTICS, so that one can see the CPU utilization, or with
AUTOTRACE to see the statistics. Compare this to the explain plan when not
using an index.
397. When should one rebuild an index? (for DBA
You can run the ‘ANALYZE INDEX VALIDATE STRUCTURE’ command on the
affected indexes – each invocation of this command creates a single row in the
INDEX_STATS view. This row is overwritten by the next ANALYZE INDEX
command, so copy the contents of the view into a local table after each
ANALYZE. The ‘badness’ of the index can then be judged by the ratio of
‘DEL_LF_ROWS’ to ‘LF_ROWS’
389. What is an Alert ?
An alert is window that appears in the middle of the screen overlaying a portion
of the current display.
438. What is an Lov?
A list of values is a single or multi column selection list displayed in a pop-up
window
444. What is Oracle Financials? (for DBA
Oracle Financials products provide organizations with solutions to a wide range
of long- and short-term accounting system issues. Regardless of the size of the
business, Oracle Financials can meet accounting management demands with:
Oracle Assets: Ensures that an organization’s property and equipment
investment is accurate and that the correct asset tax accounting strategies are
chosen.
Oracle General Ledger: Offers a complete solution to journal entry, budgeting,
allocations, consolidation, and financial reporting needs.
Oracle Inventory: Helps an organization make better inventory decisions by
minimizing stock and maximizing cash flow.
Oracle Order Entry: Provides organizations with a sophisticated order entry
system for managing customer commitments.
Oracle Payables: Lets an organization process more invoices with fewer staff
members and tighter controls. Helps save money through maximum discounts,
bank float, and prevention of duplicate payment.
Oracle Personnel: Improves the management of employee- related issues by
retaining and making available every form of personnel data.
Oracle Purchasing: Improves buying power, helps negotiate bigger discounts,
eliminates paper flow, increases financial controls, and increases productivity.
Oracle Receivables:. Improves cash flow by letting an organization process more
payments faster, without off-line research. Helps correctly account for cash,
reduce outstanding receivables, and improve collection effectiveness.
Oracle Revenue Accounting Gives an organization timely and accurate revenue
and flexible commissions reporting.
Oracle Sales Analysis: Allows for better forecasting, planning. and reporting of
sales information.
446. What is the most important module in Oracle Financials? (for DBA
The General Ledger (GL) module is the basis for all other Oracle Financial
modules. All other modules provide information to it. If you implement Oracle
Financials, you should switch your current GL system first.GL is relatively easy to
implement. You should go live with it first to give your implementation team a
chance to be familiar with Oracle Financials.
448. What is the MultiOrg and what is it used for? (for DBA
MultiOrg or Multiple Organizations Architecture allows multiple operating units
and their relationships to be defined within a single installation of Oracle
Applications. This keeps each operating unit’s transaction data separate and
secure.
Use the following query to determine if MuliOrg is intalled:
select multi_org_flag from fnd_product_groups;
449. What is the difference between Fields and FlexFields? (for DBA
A field is a position on a form that one uses to enter, view, update, or delete
information. A field prompt describes each field by telling what kind of information
appears in the field, or alternatively, what kind of information should be entered in
the field.
A flexfield is an Oracle Applications field made up of segments. Each segment
has an assigned name and a set of valid values. Oracle Applications uses
flexfields to capture information about your organization. There are two types of
flexfields: key flexfields and descriptive flexfields
470. What is Fine Grained Auditing? (for DBA
Fine Grained Auditing (DBMS_FGA) allows auditing records to be generated
when certain rows are selected from a table. A list of defined policies can be
obtained from DBA_AUDIT_POLICIES. Audit records are stored in
DBA_FGA_AUDIT_TRAIL. Look at this example:
o Add policy on table with autiting condition…
execute dbms_fga.add_policy(‘HR’, ‘EMP’, ‘policy1’, ‘deptno > 10′);
o Must ANALYZE, this feature works with CBO (Cost Based Optimizer)
analyze table EMP compute statistics;
select * from EMP where c1 = 11; — Will trigger auditing
select * from EMP where c1 = 09; — No auditing
o Now we can see the statments that triggered the auditing condition…
select sqltext from sys.fga_log$;
delete from sys.fga_log$;
472. What is Fine Grained Access Control? (for DBA
See question “What is a Virtual Private Database”.
473. What is a Virtual Private Database? (for DBA
Oracle 8i introduced the notion of a Virtual Private Database (VPD). A VPD offers
Fine-Grained Access Control (FGAC) for secure separation of data. This ensures
that users only have access to data that pertains to them. Using this option, one
could even store multiple companies’ data within the same schema, without them
knowing about it. VPD configuration is done via the DBMS_RLS (Row Level
Security) package. Select from SYS.V$VPD_POLICY to see existing VPD
configuration.
475. What is Oracle Label Security? (for DBA
Oracle Label Security (formerly called Trusted Oracle MLS RDBMS) uses the
VPD (Virtual Private Database) feature of Oracle8i to implement row level
security. Access to rows are restricted according to a user’s security sensitivity
tag or label. Oracle Label Security is configured, controlled and managed from
the Policy Manager, an Enterprise Manager-based GUI utility.
477. What is OEM (Oracle Enterprise Manager)? (for DBA
OEM is a set of systems management tools provided by Oracle Corporation for
managing the Oracle environment. It provides tools to monitor the Oracle
environment and automate tasks (both one-time and repetitive in nature) to take
database administration a step closer to “Lights Out” management.
478. Question What is PL/SQL ?
PL/SQL is a procedural language that has both interactive SQL and procedural
programming language constructs such as iteration, conditional branching.
479. What are the components of OEM? (for DBA
Oracle Enterprise Manager (OEM) has the following components:
. Management Server (OMS): Middle tier server that handles communication with
the intelligent agents. The OEM Console connects to the management server to
monitor and configure the Oracle enterprise.
. Console: This is a graphical interface from where one can schedule jobs,
events, and monitor the database. The console can be opened from a Windows
workstation, Unix XTerm (oemapp command) or Web browser session
(oem_webstage).
. Intelligent Agent (OIA): The OIA runs on the target database and takes care of
the execution of jobs and events scheduled through the Console.
. What are the advantages of having a Package ?
Increased functionality (for example,global package variables can be declared
and used by any proecdure in the package) and performance (for example all
objects of the package are parsed compiled, and loaded into memory once)
506. What are the uses of Database Trigger ?
Database triggers can be used to automatic data generation, audit data
modifications, enforce complex Integrity constraints, and customize complex
security authorizations.
507. What is a Procedure ?
A Procedure consist of a set of SQL and PL/SQL statements that are grouped
together as a unit to solve a specific problem or perform a set of related tasks.
508. What is a Package ?
A Package is a collection of related procedures, functions, variables and other
package constructs together as a unit in the database.
509. What is difference between Procedures and Functions ?
A Function returns a value to the caller where as a Procedure does not.
510. What is Database Trigger ?
A Database Trigger is procedure (set of SQL and PL/SQL statements) that is
automatically executed as a result of an insert in,update to, or delete from a
table.
511. Can the default values be assigned to actual parameters?
Yes
512. Can a primary key contain more than one columns?
Yes
515. Differentiate between TRUNCATE and DELETE?
TRUNCATE deletes much faster than DELETE
TRUNCATE
DELETE
It is a DDL statement
It is a DML statement
It is a one way trip,cannot ROLLBACK
One can Rollback
Doesn’t have selective features (where clause)
Has
Doesn’t fire database triggers
Does
It requires disabling of referential constraints.
518. What are different Oracle database objects?
-TABLES
-VIEWS
-INDEXES
-SYNONYMS
-SEQUENCES
-TABLESPACES etc
519. What is difference between SUBSTR and INSTR?
SUBSTR returns a specified portion of a string eg SUBSTR(‘BCDEF’,4) output
BCDE INSTR provides character position in which a pattern is found in a string.
eg INSTR(‘ABC-DC-F’,’-‘,2) output 7 (2nd occurence of ‘-‘
529. What is a OUTER JOIN?
Outer Join–Its a join condition used where you can query all the rows of one of
the tables in the join condition even though they don’t satisfy the join condition.
530. What is a cursor?
Oracle uses work area to execute SQL statements and store processing
information PL/SQL construct called a cursor lets you name a work area and
access its stored information A cursor is a mechanism used to fetch more than
one row in a Pl/SQl block.
531. What is the purpose of a cluster?
Oracle does not allow a user to specifically locate tables, since that is a part of
the function of the RDBMS. However, for the purpose of increasing performance,
oracle allows a developer to create a CLUSTER. A CLUSTER provides a means
for storing data from different tables together for faster retrieval than if the table
placement were left to the RDBMS.
547. How will you delete duplicating rows from a base table?
delete from table_name where rowid not in (select max(rowid) from table group
by duplicate_values_field_name); or delete duplicate_values_field_name dv from
table_name ta where rowid <(select min(rowid) from table_name tb where
ta.dv=tb.dv);

551. What is a view ?
A view is stored procedure based on one or more tables, it’s a virtual table.

552. What is difference between UNIQUE and PRIMARY KEY constraints?
A table can have only one PRIMARY KEY whereas there can be any number of
UNIQUE keys. The columns that compose PK are automatically define NOT
NULL, whereas a column that compose a UNIQUE is not automatically defined to
be mandatory must also specify the column is NOT NULL.

553. What is use of a cursor variable? How it is defined?
A cursor variable is associated with different statements at run time, which can
hold different values at run time. Static cursors can only be associated with one
run time query. A cursor variable is reference type (like a pointer in C).
Declaring a cursor variable:
TYPE type_name IS REF CURSOR RETURN return_type type_name is the
name of the reference type,return_type is a record type indicating the types of
the select list that will eventually be returned by the cursor variable.
554. How do you find the numbert of rows in a Table ?
A bad answer is count them (SELECT COUNT(*) FROM table_name)
A good answer is :-
‘By generating SQL to ANALYZE TABLE table_name COUNT STATISTICS by
querying Oracle System Catalogues (e.g. USER_TABLES or ALL_TABLES).
The best answer is to refer to the utility which Oracle released which makes it
unnecessary to do ANALYZE TABLE for each Table individually.
558. What is ON DELETE CASCADE ?
When ON DELETE CASCADE is specified ORACLE maintains referential
integrity by automatically removing dependent foreign key values if a referenced
primary or unique key value is removed.
559. What is the fastest way of accessing a row in a table ?
Using ROWID.CONSTRAINTS
560. What is difference between TRUNCATE & DELETE ?
TRUNCATE commits after deleting entire table i.e., can not be rolled back.
Database triggers do not fire on TRUNCATEDELETE allows the filtered deletion.
Deleted records can be rolled back or committed.Database triggers fire on
DELETE.
561. What is a transaction ?
Transaction is logical unit between two commits and commit and rollback.
562. What are the advantages of VIEW ?
To protect some of the columns of a table from other users.To hide complexity of
a query.To hide complexity of calculations.
563. How will you a activate/deactivate integrity constraints ?
The integrity constraints can be enabled or disabled by ALTER TABLE ENABLE
constraint/DISABLE constraint.
564. Where the integrity constraints are stored in Data Dictionary ?
The integrity constraints are stored in USER_CONSTRAINTS.
565. What is the Subquery ?
Sub query is a query whose return values are used in filtering conditions of the
main query.
567. What are the usage of SAVEPOINTS ?value in a session before
accessing next value ?
SAVEPOINTS are used to subdivide a transaction into smaller parts. It enables
rolling back part of a transaction. Maximum of five save points are allowed.
568. What is ROWID ?in a session before accessing next value ?
ROWID is a pseudo column attached to each row of a table. It is 18 character
long, blockno, rownumber are the components of ROWID.
571. What is Referential Integrity ?
Maintaining data integrity through a set of rules that restrict the values of one or
more columns of the tables based on the values of primary key or unique key of
the referenced table.
572. What is a join ? Explain the different types of joins ?
Join is a query which retrieves related columns or rows from multiple tables.Self
Join – Joining the table with itself.Equi Join – Joining two tables by equating two
common columns.Non-Equi Join – Joining two tables by equating two common
columns.Outer Join – Joining two tables in such a way that query can also
retrieve rows that do not have corresponding join value in the other table.
573. If an unique key constraint on DATE column is created, will it validate
the rows that are inserted with SYSDATE ?
It won’t, Because SYSDATE format contains time attached with it.
574. How does one stop and start the OMS? (for DBA
Use the following command sequence to stop and start the OMS (Oracle
Management Server):
oemctl start oms
oemctl status oms sysman/oem_temp
oemctl stop oms sysman/oem_temp
Windows NT/2000 users can just stop and start the required services. The
default OEM administrator is “sysman” with a password of “oem_temp”.
NOTE: Use command oemctrl instead of oemctl for Oracle 8i and below.
575. What is an Integrity Constraint ?
Integrity constraint is a rule that restricts values to a column in a table.
576. How does one create a repository? (for DBA
For OEM v2 and above, start the Oracle Enterprise Manager Configuration
Assistant (emca on Unix) to create and configure the management server and
repository. Remember to setup a backup for the repository database after
creating it.
579. What is a database link ?
Database Link is a named path through which a remote database can be
accessed.
580. How does one list one’s databases in the OEM Console? (for DBA
Follow these steps to discover databases and other services from the OEM
Console:
1. Ensure the GLOBAL_DBNAME parameter is set for all databases in your
LISTENER.ORA file (optional). These names will be listed in the OEM Console.
Please note that names entered are case sensitive. A portion of a listener.ora file:
(SID_DESC =
(GLOBAL_DBNAME = DB_name_for_OEM)
(SID_NAME = …
2. Start the Oracle Intelligent Agent on the machine you want to discover. See
section “How does one start the Oracle Intelligent Agent?”.
3. Start the OEM Console, navigate to menu “Navigator/ Discover Nodes”. The
OEM Discovery Wizard will guide you through the process of discovering your
databases and other services.
593. What utility is used to create a physical backup?
Either rman or alter tablespace begin backup will do..
594. What are the Back ground processes in Oracle and what are they.
This is one of the most frequently asked question.There are basically 9
Processes but in a general system we need to mention the first five background
processes.They do the house keeping activities for the Oracle and are common
in any system.
The various background processes in oracle are
a) Data Base Writer(DBWR) :: Data Base Writer Writes Modified blocks from
Database buffer cache to Data Files.This is required since the data is not written
whenever a transaction is commited.
b)LogWriter(LGWR) :: LogWriter writes the redo log entries to disk. Redo Log
data is generated in redo log buffer of SGA. As transaction commits and log
buffer fills, LGWR writes log entries into a online redo log file.
c) System Monitor(SMON) :: The System Monitor performs instance recovery at
instance startup.This is useful for recovery from system failure
d)Process Monitor(PMON) :: The Process Monitor peforms process recovery
when user Process fails. Pmon Clears and Frees resources that process was
using.
e) CheckPoint(CKPT) :: At Specified times, all modified database buffers in SGA
are written to data files by DBWR at Checkpoints and Updating all data files and
control files of database to indicate the most recent checkpoint
f)Archieves(ARCH) :: The Archiver copies online redo log files to archival storal
when they are busy.
g) Recoveror(RECO) :: The Recoveror is used to resolve the distributed
transaction in network
h) Dispatcher (Dnnn) :: The Dispatcher is useful in Multi Threaded Architecture
i) Lckn :: We can have upto 10 lock processes for inter instance locking in
parallel sql.
595. How many types of Sql Statements are there in Oracle
There are basically 6 types of sql statments.They are
a) Data Defination Language(DDL) :: The DDL statments define and maintain
objects and drop objects.
b) Data Manipulation Language(DML) :: The DML statments manipulate
database data.
c) Transaction Control Statements :: Manage change by DML
d) Session Control :: Used to control the properties of current session enabling
and disabling roles and changing .e.g :: Alter Statements,Set Role
e) System Control Statements :: Change Properties of Oracle Instance .e.g:: Alter
System
f) Embedded Sql :: Incorporate DDL,DML and T.C.S in Programming
Language.e.g:: Using the Sql Statements in languages such as ‘C’, Open,Fetch,
execute and close
596. What is a Transaction in Oracle
A transaction is a Logical unit of work that compromises one or more SQL
Statements executed by a single User. According to ANSI, a transaction begins
with first executable statment and ends when it is explicitly commited or rolled
back.
597. Key Words Used in Oracle
The Key words that are used in Oracle are ::
a) Commiting :: A transaction is said to be commited when the transaction makes
permanent changes resulting from the SQL statements.
b) Rollback :: A transaction that retracts any of the changes resulting from SQL
statements in Transaction.
c) SavePoint :: For long transactions that contain many SQL statements,
intermediate markers or savepoints are declared. Savepoints can be used to
divide a transactino into smaller points.
d) Rolling Forward :: Process of applying redo log during recovery is called rolling
forward.
e) Cursor :: A cursor is a handle ( name or a pointer) for the memory associated
with a specific stament. A cursor is basically an area allocated by Oracle for
executing the Sql Statement. Oracle uses an implicit cursor statement for Single
row query and Uses Explcit cursor for a multi row query.
f) System Global Area(SGA) :: The SGA is a shared memory region allocated by
the Oracle that contains Data and control information for one Oracle Instance.It
consists of Database Buffer Cache and Redo log Buffer.
g) Program Global Area (PGA) :: The PGA is a memory buffer that contains data
and control information for server process.
g) Database Buffer Cache :: Databese Buffer of SGA stores the most recently
used blocks of datatbase data.The set of database buffers in an instance is
called Database Buffer Cache.
h) Redo log Buffer :: Redo log Buffer of SGA stores all the redo log entries.
i) Redo Log Files :: Redo log files are set of files that protect altered database
data in memory that has not been written to Data Files. They are basically used
for backup when a database crashes.
j) Process :: A Process is a ‘thread of control’ or mechansim in Operating System
that executes series of steps.
603. What is in all those X$ tables? (for DBA
The following list attempts to describe some x$ tables. The list may not be
complete or accurate, but represents an attempt to figure out what information
they contain. One should generally not write queries against these tables as they
are internal to Oracle, and Oracle may change them without any prior notification.
X$K2GTE2 Kernel 2 Phase Commit Global Transaction Entry Fixed
Table
X$K2GTE Kernel 2 Phase Commit Global Transaction Entry Fixed
Table
X$BH Buffer headers contain information describing the current
contents of a piece of the buffer cache
X$KCBCBH
Cache Buffer Current Buffer Header Fixed Table. It can
predict the potential loss of decreasing the number of
database buffers. The db_block_lru_statistics parameter
has to be set to true to gather information in this table.
X$KCVFH File Header Fixed Table
X$KDNCE SGA Cache Entry Fixed Table
X$KDNST Sequence Cache Statistics Fixed Table
X$KDXHS Histogram structure Fixed Table
X$KDXST Statistics collection Fixed Table
X$KGHLU One-row summary of LRU statistics for the shared pool
X$KGLBODY Derived from X$KGLOB (col kglhdnsp = 2)
X$KGLCLUSTER Derived from X$KGLOB (col kglhdnsp = 5)
X$KGLINDEX Derived from X$KGLOB (col kglhdnsp = 4)
X$KGLLC Latch Clean-up state for library cache objects Fixed Table
X$KGLPN Library cache pin Fixed Table
X$KGLTABLE Derived from X$KGLOB (col kglhdnsp = 1)
X$KGLTR Library Cache Translation Table entry Fixed Table
X$KGLTRIGGER Derived from X$KGLOB (col kglhdnsp = 3)
X$KGLXS Library Cache Access Table
X$KKMMD Fixed table to look at what databases are mounted and
their status
X$KKSBV Cursor Cache Bind Variables
X$KSMSP Each row represents a piece of memory in the shared
pool
X$KSQDN Global database name
X$KSQST Enqueue statistics by type
X$KSUCF Cost function for each Kernel Profile (join to X$KSUPL)
X$KSUPL Resource Limit for each Kernel Profile
X$KSURU Resource Usage for each Kernel Profile (join with
X$KSUPL)
X$KSQST Gets and waits for different types of enqueues
X$KTTVS Indicate tablespace that has valid save undo segments
X$KVII Internal instance parameters set at instance initialization
X$KVIS Oracle Data Block (size_t type) variables
X$KVIT Instance internal flags, variables and parameters that can
change during the life of an instance
X$KXFPCDS Client Dequeue Statistics
X$KXFPCMS Client Messages Statistics
X$KZDOS Represent an os role as defined by the operating system
X$KZSRO Security state Role: List of enabled roles
X$LE Lock Element: each PCM lock that is used by the buffer
cache (gc_db_locks)
X$MESSAGES Displays all the different messages that can be sent to
the Background processes
X$NLS_PARAMETERS NLS database parameters
Handy X$table queries
Some handy queries based on the X$ memory tables:
. Largest # blocks you can write at any given time:
select kviival write_batch_size
from x$kvii where kviitag = ‘kcbswc’;
. See the gets and waits for different types of enqueues:
select * from x$ksqst
where ksqstget > 0;
Oracle Kernel Subsystems
Listed below are some of the important subsystems in the Oracle kernel. This
table might help you to read those dreaded trace files and internal messages. For
example, if you see messages like this, you will at least know where they come
from: OPIRIP: Uncaught error 447. Error stack:
KCF: write/open error block=0x3e800 online=1
OPI Oracle Program Interface
KK Compilation Layer – Parse SQL, compile PL/SQL
KX Execution Layer – Bind and execute SQL and PL/SQL
K2 Distributed Execution Layer – 2PC handling
NPI Network Program Interface
KZ Security Layer – Validate privs
KQ Query Layer
RPI Recursive Program Interface
KA Access Layer
KD Data Layer
KT Transaction Layer
KC Cache Layer
KS Services Layer
KJ Lock Manager Layer
KG Generic Layer
KV Kernel Variables (eg. x$KVIS and X$KVII)
S or ODS Operating System Dependencies
605. How does one change an Oracle user’s password?(for DBA
Issue the following SQL command:
ALTER USER <username> IDENTIFIED BY <new_password>;
From Oracle8 you can just type “password” from SQL*Plus, or if you need to
change another user’s password, type “password user_name”. Look at this
example:
SQL> password
Changing password for SCOTT
Old password:
New password:
Retype new password:
606. How does one create and drop database users?
Look at these examples:
CREATE USER scott
IDENTIFIED BY tiger — Assign password
DEFAULT TABLESACE tools — Assign space for table and index segments
TEMPORARY TABLESPACE temp; — Assign sort space
DROP USER scott CASCADE; — Remove user
After creating a new user, assign the required privileges:
GRANT CONNECT, RESOURCE TO scott;
GRANT DBA TO scott; — Make user a DB Administrator
Remember to give the user some space quota on its tablespaces:
ALTER USER scott QUOTA UNLIMITED ON tools;
607. Who created all these users in my database?/ Can I drop this user?
(for DBA
Oracle creates a number of default database users or schemas when a new
database is created. Below are a few of them:
SYS/CHANGE_ON_INSTALL or INTERNAL
Oracle Data Dictionary/ Catalog
Created by: ?/rdbms/admin/sql.bsq and various cat*.sql scripts
Can password be changed: Yes (Do so right after the database was created)
Can user be dropped: NO
SYSTEM/MANAGER
The default DBA user name (please do not use SYS)
Created by: ?/rdbms/admin/sql.bsq
Can password be changed: Yes (Do so right after the database was created)
Can user be dropped: NO
OUTLN/OUTLN
Stored outlines for optimizer plan stability
Created by: ?/rdbms/admin/sql.bsq
Can password be changed: Yes (Do so right after the database was created)
Can user be dropped: NO
SCOTT/TIGER, ADAMS/WOOD, JONES/STEEL, CLARK/CLOTH and
BLAKE/PAPER.
Training/ demonstration users containing the popular EMP and DEPT tables
Created by: ?/rdbms/admin/utlsampl.sql
Can password be changed: Yes
Can user be dropped: YES – Drop users cascade from all production
environments
HR/HR (Human Resources), OE/OE (Order Entry), SH/SH (Sales History).
Training/ demonstration users containing the popular EMPLOYEES and
DEPARTMENTS tables
Created by: ?/demo/schema/mksample.sql
Can password be changed: Yes
Can user be dropped: YES – Drop users cascade from all production
environments
CTXSYS/CTXSYS
Oracle interMedia (ConText Cartridge) administrator user
Created by: ?/ctx/admin/dr0csys.sql
TRACESVR/TRACE
Oracle Trace server
Created by: ?/rdbms/admin/otrcsvr.sql
DBSNMP/DBSNMP
Oracle Intelligent agent
Created by: ?/rdbms/admin/catsnmp.sql, called from catalog.sql
Can password be changed: Yes – put the new password in snmp_rw.ora file
Can user be dropped: YES – Only if you do not use the Intelligent Agents
ORDPLUGINS/ORDPLUGINS
Object Relational Data (ORD) User used by Time Series, etc.
Created by: ?/ord/admin/ordinst.sql
ORDSYS/ORDSYS
Object Relational Data (ORD) User used by Time Series, etc
Created by: ?/ord/admin/ordinst.sql
DSSYS/DSSYS
Oracle Dynamic Services and Syndication Server
Created by: ?/ds/sql/dssys_init.sql
MDSYS/MDSYS
Oracle Spatial administrator user
Created by: ?/ord/admin/ordinst.sql
AURORA$ORB$UNAUTHENTICATED/INVALID
Used for users who do not authenticate in Aurora/ORB
Created by: ?/javavm/install/init_orb.sql called from ?/javavm/install/initjvm.sql
PERFSTAT/PERFSTAT
Oracle Statistics Package (STATSPACK) that supersedes UTLBSTAT/UTLESTAT
Created by: ?/rdbms/admin/statscre.sql
Remember to change the passwords for the SYS and SYSTEM users
immediately after installation!
Except for the user SYS, there should be no problem altering these users to use
a different default and temporary tablespace.
608. How does one enforce strict password control? (for DBA
By default Oracle’s security is not extremely good. For example, Oracle will allow
users to choose single character passwords and passwords that match their
names and userids. Also, passwords don’t ever expire. This means that one can
hack an account for years without ever locking the user.
From Oracle8 one can manage passwords through profiles. Some of the things
that one can restrict:
. FAILED_LOGIN_ATTEMPTS – failed login attempts before the account is locked
. PASSWORD_LIFE_TIME – limits the number of days the same password can
be used for authentication
. PASSWORD_REUSE_TIME – number of days before a password can be
reused
. PASSWORD_REUSE_MAX – number of password changes required before the
current password can be reused
. PASSWORD_LOCK_TIME – number of days an account will be locked after
maximum failed login attempts
. PASSWORD_GRACE_TIME – number of days after the grace period begins
during which a warning is issued and login is allowed
. PASSWORD_VERIFY_FUNCTION – password complexity verification script
Look at this simple example:
CREATE PROFILE my_profile LIMIT
PASSWORD_LIFE_TIME 30;
ALTER USER scott PROFILE my_profile;
609. How does one switch to another user in Oracle? (for DBA
Users normally use the “connect” statement to connect from one database user
to another. However, DBAs can switch from one user to another without a
password. Of course it is not advisable to bridge Oracle’s security, but look at this
example: SQL> select password from dba_users where username=’SCOTT’;
PASSWORD
F894844C34402B67
SQL> alter user scott identified by lion;
User altered.
SQL> connect scott/lion
Connected.
REM Do whatever you like…
SQL> connect system/manager
Connected.
SQL> alter user scott identified by values ‘F894844C34402B67’;
User altered.
SQL> connect scott/tiger
Connected.
Note: Also see the su.sql script in the Useful Scripts and Sample Programs Page.
612. What is the difference between candidate key, unique key and primary
key
Candidate keys are the columns in the table that could be the primary keys and
the primary key is the key that has been selected to identify the rows. Unique key
is also useful for identifying the distinct rows in the table.)
613. What is concurrency
Cuncurrency is allowing simultaneous access of same data by different users.
Locks useful for accesing the database are
a) Exclusive
The exclusive lock is useful for locking the row when an insert,update or delete is
being done.This lock should not be applied when we do only select from the row.
b) Share lock
We can do the table as Share_Lock as many share_locks can be put on the
same resource.
614. Previleges and Grants
Previleges are the right to execute a particulare type of SQL statements. e.g ::
Right to Connect, Right to create, Right to resource Grants are given to the
objects so that the object might be accessed accordingly.The grant has to be
given by the owner of the object.
615. Table Space,Data Files,Parameter File, Control Files
Table Space :: The table space is useful for storing the data in the
database.When a database is created two table spaces are created.
a) System Table space :: This data file stores all the tables related to the system
and dba tables
b) User Table space :: This data file stores all the user related tables
We should have seperate table spaces for storing the tables and indexes so that
the access is fast.
Data Files :: Every Oracle Data Base has one or more physical data files.They
store the data for the database.Every datafile is associated with only one
database.Once the Data file is created the size cannot change.To increase the
size of the database to store more data we have to add data file.
Parameter Files :: Parameter file is needed to start an instance.A parameter file
contains the list of instance configuration parameters e.g.::
db_block_buffers = 500
db_name = ORA7
db_domain = u.s.acme lang
Control Files :: Control files record the physical structure of the data files and
redo log files
They contain the Db name, name and location of dbs, data files ,redo log files
and time stamp.
616. Physical Storage of the Data
The finest level of granularity of the data base are the data blocks.
Data Block :: One Data Block correspond to specific number of physical
database space
Extent :: Extent is the number of specific number of contigious data blocks.
Segments :: Set of Extents allocated for Extents. There are three types of
Segments
a) Data Segment :: Non Clustered Table has data segment data of every table is
stored in cluster data segment
b) Index Segment :: Each Index has index segment that stores data
c) Roll Back Segment :: Temporarily store ‘undo’ information
617. What are the Pct Free and Pct Used
Pct Free is used to denote the percentage of the free space that is to be left
when creating a table. Similarly Pct Used is used to denote the percentage of the
used space that is to be used when creating a table
eg.:: Pctfree 20, Pctused 40
618. What is Row Chaining
The data of a row in a table may not be able to fit the same data block.Data for
row is stored in a chain of data blocks .
619. What is a 2 Phase Commit
Two Phase commit is used in distributed data base systems. This is useful to
maintain the integrity of the database so that all the users see the same values. It
contains DML statements or Remote Procedural calls that reference a remote
object. There are basically 2 phases in a 2 phase commit.
a) Prepare Phase :: Global coordinator asks participants to prepare
b) Commit Phase :: Commit all participants to coordinator to Prepared, Read only
or abort Reply
620. What is the difference between deleting and truncating of tables
Deleting a table will not remove the rows from the table but entry is there in the
database dictionary and it can be retrieved But truncating a table deletes it
completely and it cannot be retrieved.
621. What are mutating tables
When a table is in state of transition it is said to be mutating. eg :: If a row has
been deleted then the table is said to be mutating and no operations can be done
on the table except select.
622. What are Codd Rules
Codd Rules describe the ideal nature of a RDBMS. No RDBMS satisfies all the
12 codd rules and Oracle Satisfies 11 of the 12 rules and is the only Rdbms to
satisfy the maximum number of rules.
623. What is Normalisation
Normalisation is the process of organising the tables to remove the
redundancy.There are mainly 5 Normalisation rules.
a) 1 Normal Form :: A table is said to be in 1st Normal Form when the attributes
are atomic
b) 2 Normal Form :: A table is said to be in 2nd Normal Form when all the
candidate keys are dependant on the primary key
c) 3rd Normal Form :: A table is said to be third Normal form when it is not
dependant transitively
624. What is the Difference between a post query and a pre query
A post query will fire for every row that is fetched but the pre query will fire only
once.
625. Deleting the Duplicate rows in the table
We can delete the duplicate rows in the table by using the Rowid
627. What is pseudo columns ? Name them?
A pseudocolumn behaves like a table column, but is not actually stored in the
table. You can select from pseudocolumns, but you cannot insert, update, or
delete their values. This section describes these pseudocolumns:
* CURRVAL
* NEXTVAL
* LEVEL
* ROWID
* ROWNUM
628. How many columns can table have?
The number of columns in a table can range from 1 to 254.
629. Is space acquired in blocks or extents ?
In extents .
630. what is clustered index?
In an indexed cluster, rows are stored together based on their cluster key values .
Can not applied for HASH.
677. What is Log Switch ?
The point at which ORACLE ends writing to one online redo log file and begins
writing to another is called a log switch.
678. What is On-line Redo Log?
The On-line Redo Log is a set of tow or more on-line redo files that record all
committed changes made to the database. Whenever a transaction is committed,
the corresponding redo entries temporarily stores in redo log buffers of the SGA
are written to an on-line redo log file by the background process LGWR. The online
redo log files are used in cyclical fashion.
679. Which parameter specified in the DEFAULT STORAGE clause of
CREATE TABLESPACE cannot be altered after creating the tablespace?
All the default storage parameters defined for the tablespace can be changed
using the ALTER TABLESPACE command. When objects are created their
INITIAL and MINEXTENS values cannot be changed.
680. What are the steps involved in Database Startup ?
Start an instance, Mount the Database and Open the Database.
< ? Recovery Instance in involved steps the are What>
Rolling forward to recover data that has not been recorded in data files, yet has
been recorded in the on-line redo log, including the contents of rollback
segments. Rolling back transactions that have been explicitly rolled back or have
not been committed as indicated by the rollback segments regenerated in step a.
Releasing any resources (locks) held by transactions in process at the time of the
failure. Resolving any pending distributed transactions undergoing a two-phase
commit at the time of the instance failure.
682. Can Full Backup be performed when the database is open ?
No.
683. What are the different modes of mounting a Database with the Parallel
Server ?
Exclusive Mode If the first instance that mounts a database does so in exclusive
mode, only that Instance can mount the database.
Parallel Mode If the first instance that mounts a database is started in parallel
mode, other instances that are started in parallel mode can also mount the
database.
684. What are the advantages of operating a database in ARCHIVELOG
mode over operating it in NO ARCHIVELOG mode ?
Complete database recovery from disk failure is possible only in ARCHIVELOG
mode. Online database backup is possible only in ARCHIVELOG mode.
685. What are the steps involved in Database Shutdown ?
Close the Database, Dismount the Database and Shutdown the Instance.
686. What is Archived Redo Log ?
Archived Redo Log consists of Redo Log files that have archived before being
reused.
687. What is Restricted Mode of Instance Startup ?
An instance can be started in (or later altered to be in) restricted mode so that
when the database is open connections are limited only to those whose user
accounts have been granted the RESTRICTED SESSION system privilege.
688.. What is a Synonym ?
A synonym is an alias for a table, view, sequence or program unit.
689. What is a Sequence ?
A sequence generates a serial list of unique numbers for numerical columns of a
database’s tables.
690. What is a Segment ?
A segment is a set of extents allocated for a certain logical structure.
691. What is schema?
A schema is collection of database objects of a User.
692. Describe Referential Integrity ?
A rule defined on a column (or set of columns) in one table that allows the insert
or update of a row only if the value for the column or set of columns (the
dependent value) matches a value in a column of a related table (the referenced
value). It also specifies the type of data manipulation allowed on referenced data
and the action to be performed on dependent data as a result of any action on
referenced data.
693. What is Hash Cluster ?
A row is stored in a hash cluster based on the result of applying a hash function
to the row’s cluster key value. All rows with the same hash key value are stores
together on disk.
694. What is a Private Synonyms ?
A Private Synonyms can be accessed only by the owner.
695. What is Database Link ?
A database link is a named object that describes a “path” from one database to
another
696. What is index cluster?
A cluster with an index on the cluster key.
697.What is hash cluster?
A row is stored in a hash cluster based on the result of applying a hash function
to the row’s cluster key value. All rows with the same hash key value are stores
together on disk.
698.When can hash cluster used?
Hash clusters are better choice when a table is often queried with equality
queries. For such queries the specified cluster key value is hashed. The resulting
hash key value points directly to the area on disk that stores the specified rows.
699.When can hash cluster used?
Hash clusters are better choice when a table is often queried with equality
queries. For such queries the specified cluster key value is hashed. The resulting
hash key value points directly to the area on disk that stores the specified rows.
700. What are the types of database links?
Private database link, public database link & network database link.
701. What is private database link?
Private database link is created on behalf of a specific user. A private database
link can be used only when the owner of the link specifies a global object name in
a SQL statement or in the definition of the owner’s views or procedures.
702. What is public database link?
Public database link is created for the special user group PUBLIC. A public
database link can be used when any user in the associated database specifies a
global object name in a SQL statement or object definition.
703. What is network database link?
Network database link is created and managed by a network domain service. A
network database link can be used when any user of any database in the
network specifies a global object name in a SQL statement or object definition.
704. What is data block?
Oracle database’s data is stored in data blocks. One data block corresponds to a
specific number of bytes of physical database space on disk.
705. How to define data block size?
A data block size is specified for each Oracle database when the database is
created. A database users and allocated free database space in Oracle data
blocks. Block size is specified in init.ora file and cannot be changed latter.
706. What is row chaining?
In circumstances, all of the data for a row in a table may not be able to fit in the
same data block. When this occurs, the data for the row is stored in a chain of
data block (one or more) reserved for that segment.
707. What is an extent?
An extent is a specific number of contiguous data blocks, obtained in a single
allocation and used to store a specific type of information.
708. What are the different types of segments?
Data segment, index segment, rollback segment and temporary segment.
709. What is a data segment?
Each non-clustered table has a data segment. All of the table’s data is stored in
the extents of its data segment. Each cluster has a data segment. The data of
every table in the cluster is stored in the cluster’s data segment.
709. What is an index segment?
Each index has an index segment that stores all of its data.
710. What is rollback segment?
A database contains one or more rollback segments to temporarily store “undo”
information.
711. What are the uses of rollback segment?
To generate read-consistent database information during database recovery and
to rollback uncommitted transactions by the users.
712. What is a temporary segment?
Temporary segments are created by Oracle when a SQL statement needs a
temporary work area to complete execution. When the statement finishes
execution, the temporary segment extents are released to the system for future
use.
713. What is a datafile?
Every Oracle database has one or more physical data files. A database’s data
files contain all the database data. The data of logical database structures such
as tables and indexes is physically stored in the data files allocated for a
database.
714. What are the characteristics of data files?
A data file can be associated with only one database. Once created a data file
can’t change size. One or more data files form a logical unit of database storage
called a tablespace.
715. What is a redo log?
The set of redo log files for a database is collectively known as the database
redo log.
716. What is the function of redo log?
The primary function of the redo log is to record all changes made to data.
717. What is the use of redo log information?
The information in a redo log file is used only to recover the database from a
system or media failure prevents database data from being written to a
database’s data files.
718. What does a control file contains?
– Database name
– Names and locations of a database’s files and redolog files.
– Time stamp of database creation.
719. What is the use of control file?
When an instance of an Oracle database is started, its control file is used to
identify the database and redo log files that must be opened for database
operation to proceed. It is also used in database recovery
730. Explain the difference between a hot backup and a cold backup and
the benefits associated with each.
A hot backup is basically taking a backup of the database while it is still up and
running and it must be in archive log mode. A cold backup is taking a backup of
the database while it is shut down and does not require being in archive log
mode. The benefit of taking a hot backup is that the database is still available for
use while the backup is occurring and you can recover the database to any point
in time. The benefit of taking a cold backup is that it is typically easier to
administer the backup and recovery process. In addition, since you are taking
cold backups the database does not require being in archive log mode and thus
there will be a slight performance gain as the database is not cutting archive logs
to disk.
731. You have just had to restore from backup and do not have any control
files. How would you go about bringing up this database?
I would create a text based backup control file, stipulating where on disk all the
data files where and then issue the recover command with the using backup
control file clause.
732. How do you switch from an init.ora file to a spfile?
Issue the create spfile from pfile command.
732. Explain the difference between a data block, an extent and a segment.
A data block is the smallest unit of logical storage for a database object. As
objects grow they take chunks of additional storage that are composed of
contiguous data blocks. These groupings of contiguous data blocks are called
extents. All the extents that an object takes when grouped together are
considered the segment of the database object.
733. Give two examples of how you might determine the structure of the
table DEPT.
Use the describe command or use the dbms_metadata.get_ddl package.
734. Where would you look for errors from the database engine?
In the alert log.
735. Compare and contrast TRUNCATE and DELETE for a table.
Both the truncate and delete command have the desired outcome of getting rid of
all the rows in a table. The difference between the two is that the truncate
command is a DDL operation and just moves the high water mark and produces
a now rollback. The delete command, on the other hand, is a DML operation,
which will produce a rollback and thus take longer to complete.
736. Give the reasoning behind using an index.
Faster access to data blocks in a table.
737. Give the two types of tables involved in producing a star schema and
the type of data they hold.
Fact tables and dimension tables. A fact table contains measurements while
dimension tables will contain data that will help describe the fact tables.
738. What type of index should you use on a fact table?
A Bitmap index.
739. Give two examples of referential integrity constraints.
A primary key and a foreign key.
740. A table is classified as a parent table and you want to drop and recreate
it. How would you do this without affecting the children tables?
Disable the foreign key constraint to the parent, drop the table, re-create the
table, enable the foreign key constraint.
741. Explain the difference between ARCHIVELOG mode and
NOARCHIVELOG mode and the benefits and disadvantages to each.
ARCHIVELOG mode is a mode that you can put the database in for creating a
backup of all transactions that have occurred in the database so that you can
recover to any point in time. NOARCHIVELOG mode is basically the absence of
ARCHIVELOG mode and has the disadvantage of not being able to recover to
any point in time. NOARCHIVELOG mode does have the advantage of not
having to write transactions to an archive log and thus increases the performance
of the database slightly.
742. What command would you use to create a backup control file?
Alter database backup control file to trace.
743. Give the stages of instance startup to a usable state where normal
users may access it.
STARTUP NOMOUNT – Instance startup
STARTUP MOUNT – The database is mounted
STARTUP OPEN – The database is opened
744. What column differentiates the V$ views to the GV$ views and how?
The INST_ID column which indicates the instance in a RAC environment the
information came from.
745. How would you go about generating an EXPLAIN plan?
Create a plan table with utlxplan.sql.
Use the explain plan set statement_id = ‘tst1’ into plan_table for a SQL statement
Look at the explain plan with utlxplp.sql or utlxpls.sql
746. How would you go about increasing the buffer cache hit ratio?
Use the buffer cache advisory over a given workload and then query the
v$db_cache_advice table. If a change was necessary then I would use the alter
system set db_cache_size command.
747. Explain an ORA-01555
You get this error when you get a snapshot too old within rollback. It can usually
be solved by increasing the undo retention or increasing the size of rollbacks.
You should also look at the logic involved in the application getting the error
message.
748. Explain the difference between $ORACLE_HOME and
$ORACLE_BASE.
ORACLE_BASE is the root directory for oracle. ORACLE_HOME located
beneath ORACLE_BASE is where the oracle products reside.
749. How would you determine the time zone under which a database was
operating?
select DBTIMEZONE from dual;
750. Explain the use of setting GLOBAL_NAMES equal to TRUE.
Setting GLOBAL_NAMES dictates how you might connect to a database. This
variable is either TRUE or FALSE and if it is set to TRUE it enforces database
links to have the same name as the remote database to which they are linking.
751. What command would you use to encrypt a PL/SQL application?
WRAP
752. Explain the difference between a FUNCTION, PROCEDURE and
PACKAGE.
A function and procedure are the same in that they are intended to be a
collection of PL/SQL code that carries a single task. While a procedure does not
have to return any values to the calling application, a function will return a single
value. A package on the other hand is a collection of functions and procedures
that are grouped together based on their commonality to a business function or
application.
753. Explain the use of table functions.
Table functions are designed to return a set of rows through PL/SQL logic but are
intended to be used as a normal table or view in a SQL statement. They are also
used to pipeline information in an ETL process.
(Continued on next part…)
754. Name three advisory statistics you can collect.
Buffer Cache Advice, Segment Level Statistics, & Timed Statistics
755. Where in the Oracle directory tree structure are audit traces placed?
In unix $ORACLE_HOME/rdbms/audit, in Windows the event viewer
756. Explain materialized views and how they are used.
Materialized views are objects that are reduced sets of information that have
been summarized, grouped, or aggregated from base tables. They are typically
used in data warehouse or decision support systems.
757. When a user process fails, what background process cleans up after
it?
PMON
758. What background process refreshes materialized views?
The Job Queue Processes.
759. How would you determine what sessions are connected and what
resources they are waiting for?
Use of V$SESSION and V$SESSION_WAIT
760. Describe what redo logs are.
Redo logs are logical and physical structures that are designed to hold all the
changes made to a database and are intended to aid in the recovery of a
database.
761. How would you force a log switch?
ALTER SYSTEM SWITCH LOGFILE;
762. Give two methods you could use to determine what DDL changes have
been made.
You could use Logminer or Streams
763. What does coalescing a tablespace do?
Coalescing is only valid for dictionary-managed tablespaces and de-fragments
space by combining neighboring free extents into large single extents.
764. What is the difference between a TEMPORARY tablespace and a
PERMANENT tablespace?
A temporary tablespace is used for temporary objects such as sort structures
while permanent tablespaces are used to store those objects meant to be used
as the true objects of the database.
765. Name a tablespace automatically created when you create a database.
The SYSTEM tablespace.
766. When creating a user, what permissions must you grant to allow them
to connect to the database?
Grant the CONNECT to the user.
767. How do you add a data file to a tablespace
ALTER TABLESPACE <tablespace_name> ADD DATAFILE <datafile_name>
SIZE
768. How do you resize a data file?
ALTER DATABASE DATAFILE <datafile_name> RESIZE <new_size>;
769. What view would you use to look at the size of a data file?
DBA_DATA_FILES
770. What view would you use to determine free space in a tablespace?
DBA_FREE_SPACE
771. How would you determine who has added a row to a table?
Turn on fine grain auditing for the table.
772. How can you rebuild an index?
ALTER INDEX <index_name> REBUILD;
773. Explain what partitioning is and what its benefit is.
Partitioning is a method of taking large tables and indexes and splitting them into
smaller, more manageable pieces.
774. You have just compiled a PL/SQL package but got errors, how would
you view the errors?
SHOW ERRORS
775. How can you gather statistics on a table?
The ANALYZE command.
776. How can you enable a trace for a session?
Use the DBMS_SESSION.SET_SQL_TRACE or
Use ALTER SESSION SET SQL_TRACE = TRUE;
777. What is the difference between the SQL*Loader and IMPORT utilities?
These two Oracle utilities are used for loading data into the database. The
difference is that the import utility relies on the data being produced by another
Oracle utility EXPORT while the SQL*Loader utility allows data to be loaded that
has been produced by other utilities from different data sources just so long as it
conforms to ASCII formatted or delimited files.
778. Name two files used for network connection to a database.
TNSNAMES.ORA and SQLNET.ORA
781. Can one resize tablespaces and data files? (for DBA)
One can manually increase or decrease the size of a datafile from Oracle 7.2
using the command.
ALTER DATABASE DATAFILE ‘filename2’ RESIZE 100M;
Because you can change the sizes of datafiles, you can add more space to your
database without adding more datafiles. This is beneficial if you are concerned
about reaching the maximum number of datafiles allowed in your database.
Manually reducing the sizes of datafiles allows you to reclaim unused space in
the database. This is useful for correcting errors in estimations of space
requirements.
Also, datafiles can be allowed to automatically extend if more space is required.
Look at the following command:
CREATE TABLESPACE pcs_data_ts
DATAFILE ‘c:\ora_apps\pcs\pcsdata1.dbf’ SIZE 3M
AUTOEXTEND ON NEXT 1M MAXSIZE UNLIMITED
DEFAULT STORAGE (INITIAL 10240
NEXT 10240
MINEXTENTS 1
MAXEXTENTS UNLIMITED
PCTINCREASE 0)
ONLINE
PERMANENT;
782. What is SAVE POINT ?
For long transactions that contain many SQL statements, intermediate markers
or savepoints can be declared which can be used to divide a transaction into
smaller parts. This allows the option of later rolling back all work performed from
the current point in the transaction to a declared savepoint within the transaction.
784. Can one rename a tablespace? (for DBA)
No, this is listed as Enhancement Request 148742. Workaround:
Export all of the objects from the tablespace
Drop the tablespace including contents
Recreate the tablespace
Import the objects
787. How does one create a standby database? (for DBA)
While your production database is running, take an (image copy) backup and
restore it on duplicate hardware. Note that an export will not work!!!
On your standby database, issue the following commands:
ALTER DATABASE CREATE STANDBY CONTROLFILE AS ‘filename’;
ALTER DATABASE MOUNT STANDBY DATABASE;
RECOVER STANDBY DATABASE;
On systems prior to Oracle 8i, write a job to copy archived redo log files from the
primary database to the standby system, and apply the redo log files to the
standby database (pipe it). Remember the database is recovering and will
prompt you for the next log file to apply.
Oracle 8i onwards provide an “Automated Standby Database” feature, which will
send archived, log files to the remote site via NET8, and apply then to the
standby database.
When one needs to activate the standby database, stop the recovery process
and activate it:
ALTER DATABASE ACTIVATE STANDBY DATABASE;
788.How does one give developers access to trace files (required as input
to tkprof)? (for DBA)
The “alter session set sql_trace=true” command generates trace files in
USER_DUMP_DEST that can be used by developers as input to tkprof. On Unix
the default file mask for these files are “rwx r– —“.
There is an undocumented INIT.ORA parameter that will allow everyone to read
(rwx r-r–) these trace files:
_trace_files_public = true
Include this in your INIT.ORA file and bounce your database for it to take effect.
789. What are the responsibilities of a Database Administrator ?
Installing and upgrading the Oracle Server and application tools. Allocating
system storage and planning future storage requirements for the database
system. Managing primary database structures (tablespaces) Managing primary
objects (table,views,indexes) Enrolling users and maintaining system security.
Ensuring compliance with Oralce license agreement Controlling and monitoring
user access to the database. Monitoring and optimizing the performance of the
database. Planning for backup and recovery of database information. Maintain
archived data on tape Backing up and restoring the database. Contacting Oracle
Corporation for technical support.
790. What is a trace file and how is it created ?
Each server and background process can write an associated trace file. When an
internal error is detected by a process or user process, it dumps information
about the error to its trace. This can be used for tuning the database.
791. What are the roles and user accounts created automatically with the
database?
DBA – role Contains all database system privileges.
SYS user account – The DBA role will be assigned to this account. All of the base
tables and views for the database’s dictionary are store in this schema and are
manipulated only by ORACLE. SYSTEM user account – It has all the system
privileges for the database and additional tables and views that display
administrative information and internal tables and views used by oracle tools are
created using this username.
792. What are the minimum parameters should exist in the parameter file
(init.ora) ?
DB NAME – Must set to a text string of no more than 8 characters and it will be
stored inside the datafiles, redo log files and control files and control file while
database creation.
DB_DOMAIN – It is string that specifies the network domain where the database
is created. The global database name is identified by setting these parameters
(DB_NAME & DB_DOMAIN) CONTORL FILES – List of control filenames of the
database. If name is not mentioned then default name will be used.
DB_BLOCK_BUFFERS – To determine the no of buffers in the buffer cache in
SGA.
PROCESSES – To determine number of operating system processes that can be
connected to ORACLE concurrently. The value should be 5 (background
process) and additional 1 for each user.
ROLLBACK_SEGMENTS – List of rollback segments an ORACLE instance
acquires at database startup. Also optionally
LICENSE_MAX_SESSIONS,LICENSE_SESSION_WARNING and
LICENSE_MAX_USERS.
793. Why and when should I backup my database? (for DBA
Backup and recovery is one of the most important aspects of a DBAs job. If you
lose your company’s data, you could very well lose your job. Hardware and
software can always be replaced, but your data may be irreplaceable!
Normally one would schedule a hierarchy of daily, weekly and monthly backups,
however consult with your users before deciding on a backup schedule. Backup
frequency normally depends on the following factors:
. Rate of data change/ transaction rate
. Database availability/ Can you shutdown for cold backups?
. Criticality of the data/ Value of the data to the company
. Read-only tablespace needs backing up just once right after you make it readonly
. If you are running in archivelog mode you can backup parts of a database over
an extended cycle of days
. If archive logging is enabled one needs to backup archived log files timeously to
prevent database freezes
. Etc.
Carefully plan backup retention periods. Ensure enough backup media (tapes)
are available and that old backups are expired in-time to make media available
for new backups. Off-site vaulting is also highly recommended.
Frequently test your ability to recover and document all possible scenarios.
Remember, it’s the little things that will get you. Most failed recoveries are a
result of organizational errors and miscommunications.
794. What strategies are available for backing-up an Oracle database? (for
DBA
The following methods are valid for backing-up an Oracle database:
Export/Import – Exports are “logical” database backups in that they extract logical
definitions and data from the database to a file.
Cold or Off-line Backups – Shut the database down and backup up ALL data, log,
and control files.
Hot or On-line Backups – If the databases are available and in ARCHIVELOG
mode, set the tablespaces into backup mode and backup their files. Also
remember to backup the control files and archived redo log files.
RMAN Backups – While the database is off-line or on-line, use the “rman” utility to
backup the database.
It is advisable to use more than one of these methods to backup your database.
For example, if you choose to do on-line database backups, also cover yourself
by doing database exports. Also test ALL backup and recovery scenarios
carefully. It is better to be save than sorry.
Regardless of your strategy, also remember to backup all required software
libraries, parameter files, password files, etc. If your database is in
ARCGIVELOG mode, you also need to backup archived log files.
795. What is the difference between online and offline backups? (for DBA
A hot backup is a backup performed while the database is online and available
for read/write. Except for Oracle exports, one can only do on-line backups when
running in ARCHIVELOG mode.
A cold backup is a backup performed while the database is off-line and
unavailable to its users.
796. What is the difference between restoring and recovering? (for DBA
Restoring involves copying backup files from secondary storage (backup media)
to disk. This can be done to replace damaged files or to copy/move a database
to a new location.
Recovery is the process of applying redo logs to the database to roll it forward.
One can roll-forward until a specific point-in-time (before the disaster occurred),
or roll-forward until the last transaction recorded in the log files. Sql> connect
SYS as SYSDBA
Sql> RECOVER DATABASE UNTIL TIME ‘2001-03-06:16:00:00’ USING
BACKUP CONTROLFILE;
797. How does one backup a database using the export utility? (for DBA
Oracle exports are “logical” database backups (not physical) as they extract data
and logical definitions from the database into a file. Other backup strategies
normally back-up the physical data files.
One of the advantages of exports is that one can selectively re-import tables,
however one cannot roll-forward from an restored export file. To completely
restore a database from an export file one practically needs to recreate the entire
database.
Always do full system level exports (FULL=YES). Full exports include more
information about the database in the export file than user level exports.
812. What tuning indicators can one use? (for DBA
The following high-level tuning indicators can be used to establish if a database
is performing optimally or not:
. Buffer Cache Hit Ratio
Formula: Hit Ratio = (Logical Reads – Physical Reads) / Logical Reads
Action: Increase DB_CACHE_SIZE (DB_BLOCK_BUFFERS prior to 9i) to
increase hit ratio
. Library Cache Hit Ratio
Action: Increase the SHARED_POOL_SIZE to increase hit ratio
813. What tools/utilities does Oracle provide to assist with performance
tuning? (for DBA
Oracle provide the following tools/ utilities to assist with performance monitoring
and tuning:
. TKProf
. UTLBSTAT.SQL and UTLESTAT.SQL – Begin and end stats monitoring
. Statspack
. Oracle Enterprise Manager – Tuning Pack
814. What is STATSPACK and how does one use it? (for DBA
Statspack is a set of performance monitoring and reporting utilities provided by
Oracle from Oracle8i and above. Statspack provides improved BSTAT/ESTAT
functionality, though the old BSTAT/ESTAT scripts are still available. For more
information about STATSPACK, read the documentation in file
$ORACLE_HOME/rdbms/admin/spdoc.txt.
Install Statspack:
cd $ORACLE_HOME/rdbms/admin
sqlplus “/ as sysdba” @spdrop.sql — Install Statspack –
sqlplus “/ as sysdba” @spcreate.sql– Enter tablespace names when prompted
Use Statspack:
sqlplus perfstat/perfstat
exec statspack.snap; — Take a performance snapshots
exec statspack.snap;
o Get a list of snapshots
select SNAP_ID, SNAP_TIME from STATS$SNAPSHOT;
@spreport.sql — Enter two snapshot id’s for difference report
Other Statspack Scripts:
. sppurge.sql – Purge a range of Snapshot Id’s between the specified begin and
end Snap Id’s
. spauto.sql – Schedule a dbms_job to automate the collection of STATPACK
statistics
. spcreate.sql – Installs the STATSPACK user, tables and package on a database
(Run as SYS).
. spdrop.sql – Deinstall STATSPACK from database (Run as SYS)
. sppurge.sql – Delete a range of Snapshot Id’s from the database
. spreport.sql – Report on differences between values recorded in two snapshots
. sptrunc.sql – Truncates all data in Statspack tables
815. What are the common RMAN errors (with solutions)? (for DBA
Some of the common RMAN errors are:
RMAN-20242: Specification does not match any archivelog in the recovery
catalog.
Add to RMAN script: sql ‘alter system archive log current’;
RMAN-06089: archived log xyz not found or out of sync with catalog
Execute from RMAN: change archivelog all validate;
822. What is mean by Program Global Area (PGA) ?
It is area in memory that is used by a Single Oracle User Process.
830. How does one manage Oracle database users? (for DBA
Oracle user accounts can be locked, unlocked, forced to choose new passwords,
etc. For example, all accounts except SYS and SYSTEM will be locked after
creating an Oracle9iDB database using the DB Configuration Assistant (dbca).
DBA’s must unlock these accounts to make them available to users.
Look at these examples:
ALTER USER scott ACCOUNT LOCK — lock a user account
ALTER USER scott ACCOUNT UNLOCK; — unlocks a locked users account
ALTER USER scott PASSWORD EXPIRE; — Force user to choose a new
password
831. How does one tune Oracle Wait events? (for DBA
Some wait events from V$SESSION_WAIT and V$SYSTEM_EVENT views:
Event Name: Tuning Recommendation:
db file sequential
read
Tune SQL to do less I/O. Make sure all objects are analyzed.
Redistribute I/O across disks.
buffer busy waits Increase DB_CACHE_SIZE (DB_BLOCK_BUFFERS prior to 9i)/
Analyze contention from SYS.V$BH
log buffer
spaces
Increase LOG_BUFFER parameter or move log files to faster
disks
832. What is the difference between DBFile Sequential and Scattered
Reads?(for DBA
Both “db file sequential read” and “db file scattered read” events signify time
waited for I/O read requests to complete. Time is reported in 100’s of a second
for Oracle 8i releases and below, and 1000’s of a second for Oracle 9i and
above. Most people confuse these events with each other as they think of how
data is read from disk. Instead they should think of how data is read into the SGA
buffer cache.
db file sequential read:
A sequential read operation reads data into contiguous memory (usually a singleblock
read with p3=1, but can be multiple blocks). Single block I/Os are usually
the result of using indexes. This event is also used for rebuilding the controlfile
and reading datafile headers (P2=1). In general, this event is indicative of disk
contention on index reads.
db file scattered read:
Similar to db file sequential reads, except that the session is reading multiple
data blocks and scatters them into different discontinuous buffers in the SGA.
This statistic is NORMALLY indicating disk contention on full table scans. Rarely,
data from full table scans could be fitted into a contiguous buffer area, these
waits would then show up as sequential reads instead of scattered reads.
The following query shows average wait time for sequential versus scattered
reads:
prompt “AVERAGE WAIT TIME FOR READ REQUESTS”
select a.average_wait “SEQ READ”, b.average_wait “SCAT READ”
from sys.v_$system_event a, sys.v_$system_event b
where a.event = ‘db file sequential read’
and b.event = ‘db file scattered read’;
836. How does one use ORADEBUG from Server Manager/ SQL*Plus? (for
DBA
Execute the “ORADEBUG HELP” command from svrmgrl or sqlplus to obtain a
list of valid ORADEBUG commands. Look at these examples:
SQLPLUS> REM Trace SQL statements with bind variables
SQLPLUS> oradebug setospid 10121
Oracle pid: 91, Unix process pid: 10121, image: oracleorcl
SQLPLUS> oradebug EVENT 10046 trace name context forever, level 12
Statement processed.
SQLPLUS> ! vi /app/oracle/admin/orcl/bdump/ora_10121.trc
SQLPLUS> REM Trace Process Statistics
SQLPLUS> oradebug setorapid 2
Unix process pid: 1436, image: ora_pmon_orcl
SQLPLUS> oradebug procstat
Statement processed.
SQLPLUS>> oradebug TRACEFILE_NAME
/app/oracle/admin/orcl/bdump/pmon_1436.trc
SQLPLUS> REM List semaphores and shared memory segments in use
SQLPLUS> oradebug ipc
SQLPLUS> REM Dump Error Stack
SQLPLUS> oradebug setospid <pid>
SQLPLUS> oradebug event immediate trace name errorstack level 3
SQLPLUS> REM Dump Parallel Server DLM locks
SQLPLUS> oradebug lkdebug -a convlock
SQLPLUS> oradebug lkdebug -a convres
SQLPLUS> oradebug lkdebug -r <resource handle> (i.e 0x8066d338 from
convres dump)
837. Are there any undocumented commands in Oracle? (for DBA
Sure there are, but it is hard to find them. Look at these examples:
From Server Manager (Oracle7.3 and above): ORADEBUG HELP
It looks like one can change memory locations with the ORADEBUG POKE
command. Anyone brave enough to test this one for us? Previously this
functionality was available with ORADBX (ls -l
$ORACLE_HOME/rdbms/lib/oradbx.o; make -f oracle.mk oradbx) SQL*Plus:
ALTER SESSION SET CURRENT_SCHEMA = SYS;
849. WHAT IS RMAN ? (for DBA
Recovery Manager is a tool that: manages the process of creating backups and
also manages the process of restoring and recovering from them.
850. WHY USE RMAN ? (for DBA
No extra costs …Its available free
?RMAN introduced in Oracle 8 it has become simpler with newer versions and
easier than user managed backups
?Proper security
?You are 100% sure your database has been backed up.
?Its contains detail of the backups taken etc in its central repository
Facility for testing validity of backups also commands like crosscheck to check
the status of backup.
Faster backups and restores compared to backups without RMAN
RMAN is the only backup tool which supports incremental backups.
Oracle 10g has got further optimized incremental backup which has resulted in
improvement of performance during backup and recovery time
Parallel operations are supported
Better querying facility for knowing different details of backup
No extra redo generated when backup is taken..compared to online
backup without RMAN which results in saving of space in hard disk
RMAN an intelligent tool
Maintains repository of backup metadata
Remembers backup set location
Knows what need to backed up
Knows what is required for recovery
Knows what backups are redundant
UNDERSTANDING THE RMAN ARCHITECTURE
An oracle RMAN comprises of
RMAN EXECUTABLE This could be present and fired even through client side
TARGET DATABASE This is the database which needs to be backed up .
RECOVERY CATALOG Recovery catalog is optional otherwise backup details
are stored in target database controlfile .
It is a repository of information queried and updated by Recovery Manager
It is a schema or user stored in Oracle database. One schema can support many
databases
It contains information about physical schema of target database datafile and
archive log ,backup sets and pieces Recovery catalog is a must in following
scenarios
. In order to store scripts
. For tablespace point in time recovery
Media Management Software
Media Management software is a must if you are using RMAN for storing backup
in tape drive directly.
Backups in RMAN
Oracle backups in RMAN are of the following type
RMAN complete backup OR RMAN incremental backup
These backups are of RMAN proprietary nature
IMAGE COPY
The advantage of uing Image copy is its not in RMAN proprietary format..
Backup Format
RMAN backup is not in oracle format but in RMAN format. Oracle backup
comprises of backup sets and it consists of backup pieces. Backup sets are
logical entity In oracle 9i it gets stored in a default location There are two type of
backup sets Datafile backup sets, Archivelog backup sets One more important
point of data file backup sets is it do not include empty blocks. A backup set
would contain many backup pieces.
A single backup piece consists of physical files which are in RMAN proprietary
format.
Example of taking backup using RMAN
Taking RMAN Backup
In non archive mode in dos prompt type
RMAN
You get the RMAN prompt
RMAN > Connect Target
Connect to target database : Magic
using target database controlfile instead of recovery catalog
Lets take a simple backup of database in non archive mode
shutdown immediate ; – – Shutdowns the database
startup mount
backup database ;- its start backing the database
alter database open;
We can fire the same command in archive log mode
And whole of datafiles will be backed
Backup database plus archivelog;
Restoring database
Restoring database has been made very simple in 9i .
It is just
Restore database..
RMAN has become intelligent to identify which datafiles has to be restored
and the location of backuped up file.
Oracle Enhancement for RMAN in 10 G
Flash Recovery Area
Right now the price of hard disk is falling. Many dba are taking oracle database
backup inside the hard disk itself since it results in lesser mean time between
recoverability.
The new parameter introduced is
DB_RECOVERY_FILE_DEST = /oracle/flash_recovery_area
By configuring the RMAN RETENTION POLICY the flash recovery area will
automatically delete obsolete backups and archive logs that are no longer
required based on that configuration Oracle has introduced new features in
incremental backup
Change Tracking File
Oracle 10g has the facility to deliver faster incrementals with the implementation
of changed tracking file feature.This will results in faster backups lesser space
consumption and also reduces the time needed for daily backups
Incrementally Updated Backups
Oracle database 10g Incrementally Updates Backup features merges the image
copy of a datafile with RMAN incremental backup. The resulting image copy is
now updated with block changes captured by incremental backups.The merging
of the image copy and incremental backup is initiated with RMAN recover
command. This results in faster recovery.
Binary compression technique reduces backup space usage by 50-75%.
With the new DURATION option for the RMAN BACKUP command, DBAs can
weigh backup performance against system service level requirements. By
specifying a duration, RMAN will automatically calculate the appropriate backup
rate; in addition, DBAs can optionally specify whether backups should minimize
time or system load.
New Features in Oem to identify RMAN related backup like backup pieces,
backup sets and image copy
Oracle 9i New features Persistent RMAN Configuration
A new configure command has been introduced in Oracle 9i , that lets you
configure various features including automatic channels, parallelism ,backup
options, etc.
These automatic allocations and options can be overridden by commands in a
RMAN command file.
Controlfile Auto backups
Through this new feature RMAN will automatically perform a controlfile auto
backup. after every backup or copy command.
Block Media Recovery
If we can restore a few blocks rather than an entire file we only need few blocks.
We even dont need to bring the data file offline.
Syntax for it as follows
Block Recover datafile 8 block 22;
Configure Backup Optimization
Prior to 9i whenever we backed up database using RMAN our backup also used
take backup of read only table spaces which had already been backed up and
also the same with archive log too.
Now with 9i backup optimization parameter we can prevent repeat backup of
read only tablespace and archive log. The command for this is as follows
Configure backup optimization on
Archive Log failover
If RMAN cannot read a block in an archived log from a destination. RMAN
automatically attempts to read from an alternate location this is called as archive
log failover
There are additional commands like
backup database not backed up since time ’31-jan-2002 14:00:00′
Do not backup previously backed up files
(say a previous backup failed and you want to restart from where it left off).
Similar syntax is supported for restores
backup device sbt backup set all Copy a disk backup to tape
(backing up a backup
Additionally it supports
. Backup of server parameter file
. Parallel operation supported
. Extensive reporting available
. Scripting
. Duplex backup sets
. Corrupt block detection
. Backup archive logs
Pitfalls of using RMAN
Previous to version Oracle 9i backups were not that easy which means you had
to allocate a channel compulsorily to take backup You had to give a run etc . The
syntax was a bit complex …RMAN has now become very simple and easy to
use..
If you changed the location of backup set it is compulsory for you to register it
using RMAN or while you are trying to restore backup It resulted in hanging
situations
There is no method to know whether during recovery database restore is going to
fail because of missing archive log file.
Compulsory Media Management only if using tape backup
Incremental backups though used to consume less space used to be slower
since it used to read the entire database to find the changed blocks and also
They have difficult time streaming the tape device. .
Considerable improvement has been made in 10g to optimize the algorithm to
handle changed block.
Observation
Introduced in Oracle 8 it has become more powerful and simpler with newer
version of Oracle 9 and 10 g.
So if you really don’t want to miss something critical please start using RMAN.
854. What kind of jobs can one schedule with OEM? (for DBA
OEM comes with pre-defined jobs like Export, Import, run OS commands, run sql
scripts, SQL*Plus commands etc. It also gives you the flexibility of scheduling
custom jobs written with the TCL language.
855. What are the pre requisites ?
I. to modify data type of a column ? ii. to add a column with NOT NULL constraint
? To Modify the datatype of a column the column must be empty. to add a column
with NOT NULL constrain, the table must be empty.
856. How does one backout events and jobs during maintenance slots? (for
DBA
Managemnet and data collection activity can be suspended by imposing a
blackout. Look at these examples:
agentctl start blackout # Blackout the entrire agent
agentctl stop blackout # Resume normal monitoring and management
agentctl start blackout ORCL # Blackout database ORCL
agentctl stop blackout ORCL # Resume normal monitoring and management
agentctl start blackout -s jobs -d 00:20 # Blackout jobs for 20 minutes
858. What is the Oracle Intelligent Agent? (for DBA
The Oracle Intelligent Agent (OIA) is an autonomous process that needs to run
on a remote node in the network to make the node OEM manageable. The
Oracle Intelligent Agent is responsible for:
. Discovering targets that can be managed (Database Servers, Net8 Listeners,
etc.);
. Monitoring of events registered in Enterprise Manager; and
. Executing tasks associated with jobs submitted to Enterprise Manager.
859. How does one start the Oracle Intelligent Agent? (for DBA
One needs to start an OIA (Oracle Intelligent Agent) process on all machines that
will to be managed via OEM.
For OEM 9i and above:
agentctl start agent
agentctl stop agent
For OEM 2.1 and below:
lsnrctl dbsnmp_start
lsnrctl dbsnmp_status
On Windows NT, start the “OracleAgent” Service.
If the agent doesn’t want to start, ensure your environment variables are set
correctly and delete the following files before trying again:
1) In $ORACLE_HOME/network/admin: snmp_ro.ora and snmp_rw.ora.
2) Also delete ALL files in $ORACLE_HOME/network/agent/.
Can one write scripts to send alert messages to the console?
Start the OEM console and create a new event. Select option “Enable Unsolicited
Event”. Select test “Unsolicited Event”. When entering the parameters, enter
values similar to these:
Event Name: /oracle/script/myalert
Object: *
Severity: *
Message: *
One can now write the script and invoke the oemevent command to send alerts
to the console. Look at this example: oemevent /oracle/script/myalert
DESTINATION alert “My custom error message” where DESTINATION is the
same value as entered in the “Monitored Destinations” field when you’ve
registered the event in the OEM Console.
860. Where can one get more information about TCL? (for DBA
One can write custom event checking routines for OEM using the TCL (Tool
Command Language) language. Check the following sites for more information
about TCL:
. The Tcl Developer Xchange – download and learn about TCL
. OraTCL at Sourceforge – Download the OraTCL package
. Tom Poindexter’s Tcl Page – Oratcl was originally written by Tom Poindexter
861. Are there any troubleshooting tips for OEM? (for DBA
. Create the OEM repository with a user (which will manage the OEM) and store
it in a tablespace that does not share any data with other database users. It is a
bad practice to create the repository with SYS and System.
. If you are unable to launch the console or there is a communication problem
with the intelligent agent (daemon). Ensure OCX files are registered. Type the
following in the DOS prompt (the current directory should be
$ORACLE_HOME\BIN:
C:\Orawin95\Bin> RegSvr32 mmdx32.OCX
C:\Orawin95\Bin> RegSvr32 vojt.OCX
. If you have a problem starting the Oracle Agent
Solution A: Backup the *.Q files and Delete all the *.Q Files
($Oracle_home/network/agent folder)
Backup and delete SNMP_RO.ora, SNMP_RW.ora, dbsnmp.ver and services.ora
files ($Oracle_Home/network/admin folder) Start the Oracle Agent service.
Solution B: Your version of Intelligent Agent could be buggy. Check with Oracle
for any available patches. For example, the Intelligent Agent that comes with
Oracle 8.0.4 is buggy.
Sometimes you get a Failed status for the job that was executed successfully.
Check the log to see the results of the execution rather than relying on this
status.
862. What is import/export and why does one need it? (for DBA
The Oracle export (EXP) and import (IMP) utilities are used to perform logical
database backup and recovery. They are also used to move Oracle data from
one machine, database or schema to another.
The imp/exp utilities use an Oracle proprietary binary file format and can thus
only be used between Oracle databases. One cannot export data and expect to
import it into a non-Oracle database. For more information on how to load and
unload data from files, read the SQL*Loader FAQ.
The export/import utilities are also commonly used to perform the following tasks:
. Backup and recovery (small databases only)
. Reorganization of data/ Eliminate database fragmentation
. Detect database corruption. Ensure that all the data can be read.
. Transporting tablespaces between databases
. Etc.
867. How does one use the import/export utilities? (for DBA
Look for the “imp” and “exp” executables in your $ORACLE_HOME/bin directory.
One can run them interactively, using command line parameters, or using
parameter files. Look at the imp/exp parameters before starting. These
parameters can be listed by executing the following commands: “exp help=yes”
or “imp help=yes”.
The following examples demonstrate how the imp/exp utilities can be used:
exp scott/tiger file=emp.dmp log=emp.log tables=emp rows=yes indexes=no
exp scott/tiger file=emp.dmp tables=(emp,dept)
imp scott/tiger file=emp.dmp full=yes
imp scott/tiger file=emp.dmp fromuser=scott touser=scott tables=dept
exp userid=scott/tiger@orcl parfile=export.txt
… where export.txt contains:
BUFFER=100000
FILE=account.dmp
FULL=n
OWNER=scott
GRANTS=y
COMPRESS=y
NOTE: If you do not like command line utilities, you can import and export data
with the “Schema Manager” GUI that ships with Oracle Enterprise Manager
(OEM).
868. What are the types of visual attribute settings?
Custom Visual attributes Default visual attributes Named Visual attributes.
Window
869. Can one export a subset of a table? (for DBA
From Oracle8i one can use the QUERY= export parameter to selectively unload
a subset of the data from a table. Look at this example:
exp scott/tiger tables=emp query=\”where deptno=10\”
870. What are the two ways to incorporate images into a oracle forms
application?
Boilerplate Images
Image_items
871. Can one monitor how fast a table is imported? (for DBA
If you need to monitor how fast rows are imported from a running import job, try
one of the following methods:
Method 1:
select substr(sql_text,instr(sql_text,’INTO “‘),30) table_name,
rows_processed,
round((sysdate-to_date(first_load_time,’yyyy-mm-dd hh24:mi:ss’))*24*60,1)
minutes,
trunc(rows_processed/((sysdate-to_date(first_load_time,’yyyy-mm-dd
hh24:mi:ss’))*24*60)) rows_per_min
from sys.v_$sqlarea
where sql_text like ‘INSERT %INTO “%’
and command_type = 2
and open_versions > 0;
For this to work one needs to be on Oracle 7.3 or higher (7.2 might also be OK).
If the import has more than one table, this statement will only show information
about the current table being imported.
Contributed by Osvaldo Ancarola, Bs. As. Argentina.
Method 2:
Use the FEEDBACK=n import parameter. This command will tell IMP to display a
dot for every N rows imported.
872. Can one import tables to a different tablespace? (for DBA
Oracle offers no parameter to specify a different tablespace to import data into.
Objects will be re-created in the tablespace they were originally exported from.
One can alter this behaviour by following one of these procedures: Pre-create the
table(s) in the correct tablespace:
. Import the dump file using the INDEXFILE= option
. Edit the indexfile. Remove remarks and specify the correct tablespaces.
. Run this indexfile against your database, this will create the required tables in
the appropriate tablespaces
. Import the table(s) with the IGNORE=Y option.
Change the default tablespace for the user:
. Revoke the “UNLIMITED TABLESPACE” privilege from the user
. Revoke the user’s quota from the tablespace from where the object was
exported. This forces the import utility to create tables in the user’s default
tablespace.
. Make the tablespace to which you want to import the default tablespace for the
user
. Import the table
875. What is SQL*Loader and what is it used for? (for DBA
SQL*Loader is a bulk loader utility used for moving data from external files into
the Oracle database. Its syntax is similar to that of the DB2 Load utility, but
comes with more options. SQL*Loader supports various load formats, selective
loading, and multi-table loads.
876. How does one use the SQL*Loader utility? (for DBA
One can load data into an Oracle database by using the sqlldr (sqlload on some
platforms) utility. Invoke the utility without arguments to get a list of available
parameters. Look at the following example:
sqlldr scott/tiger control=loader.ctl
This sample control file (loader.ctl) will load an external data file containing
delimited data:
load data
infile ‘c:\data\mydata.csv’
into table emp
fields terminated by “,” optionally enclosed by ‘”‘
( empno, empname, sal, deptno )
The mydata.csv file may look like this:
10001,”Scott Tiger”, 1000, 40
10002,”Frank Naude”, 500, 20
Another Sample control file with in-line data formatted as fix length records. The
trick is to specify “*” as the name of the data file, and use BEGINDATA to start
the data section in the control file.
load data
infile *
replace
into table departments
( dept position (02:05) char(4),
deptname position (08:27) char(20)
)
begindata
COSC COMPUTER SCIENCE
ENGL ENGLISH LITERATURE
MATH MATHEMATICS
POLY POLITICAL SCIENCE
878. Is there a SQL*Unloader to download data to a flat file? (for DBA
Oracle does not supply any data unload utilities. However, you can use SQL*Plus
to select and format your data and then spool it to a file:
set echo off newpage 0 space 0 pagesize 0 feed off head off trimspool on
spool oradata.txt
select col1 || ‘,’ || col2 || ‘,’ || col3
from tab1
where col2 = ‘XYZ’;
spool off
Alternatively use the UTL_FILE PL/SQL package:
rem Remember to update initSID.ora, utl_file_dir=’c:\oradata’ parameter
declare
fp utl_file.file_type;
begin
fp := utl_file.fopen(‘c:\oradata’,’tab1.txt’,’w’);
utl_file.putf(fp, ‘%s, %s\n’, ‘TextField’, 55);
utl_file.fclose(fp);
end;
/
You might also want to investigate third party tools like SQLWays from Ispirer
Systems, TOAD from Quest, or ManageIT Fast Unloader from CA to help you
unload data from Oracle.
879. Can one load variable and fix length data records? (for DBA
Yes, look at the following control file examples. In the first we will load delimited
data (variable length):
LOAD DATA
INFILE *
INTO TABLE load_delimited_data
FIELDS TERMINATED BY “,” OPTIONALLY ENCLOSED BY ‘”‘
TRAILING NULLCOLS
( data1,
data2
)
BEGINDATA
11111,AAAAAAAAAA
22222,”A,B,C,D,”
If you need to load positional data (fixed length), look at the following control file
example:
LOAD DATA
INFILE *
INTO TABLE load_positional_data
( data1 POSITION(1:5),
data2 POSITION(6:15)
)
BEGINDATA
11111AAAAAAAAAA
22222BBBBBBBBBB
Can one skip header records load while loading?
Use the “SKIP n” keyword, where n = number of logical rows to skip. Look at this
example:
LOAD DATA
INFILE *
INTO TABLE load_positional_data
SKIP 5
( data1 POSITION(1:5),
data2 POSITION(6:15)
)
BEGINDATA
11111AAAAAAAAAA
22222BBBBBBBBBB
880. Can one modify data as it loads into the database? (for DBA
Data can be modified as it loads into the Oracle Database. Note that this only
applies for the conventional load path and not for direct path loads.
LOAD DATA
INFILE *
INTO TABLE modified_data
( rec_no “my_db_sequence.nextval”,
region CONSTANT ’31’,
time_loaded “to_char(SYSDATE, ‘HH24:MI’)”,
data1 POSITION(1:5) “:data1/100”,
data2 POSITION(6:15) “upper(:data2)”,
data3 POSITION(16:22)”to_date(:data3, ‘YYMMDD’)”
)
BEGINDATA
11111AAAAAAAAAA991201
22222BBBBBBBBBB990112
LOAD DATA
INFILE ‘mail_orders.txt’
BADFILE ‘bad_orders.txt’
APPEND
INTO TABLE mailing_list
FIELDS TERMINATED BY “,”
( addr,
city,
state,
zipcode,
mailing_addr “decode(:mailing_addr, null, :addr, :mailing_addr)”,
mailing_city “decode(:mailing_city, null, :city, :mailing_city)”,
mailing_state
)
881.Can one load data into multiple tables at once? (for DBA
Look at the following control file:
LOAD DATA
INFILE *
REPLACE
INTO TABLE emp
WHEN empno != ‘ ‘
( empno POSITION(1:4) INTEGER EXTERNAL,
ename POSITION(6:15) CHAR,
deptno POSITION(17:18) CHAR,
mgr POSITION(20:23) INTEGER EXTERNAL
)
INTO TABLE proj
WHEN projno != ‘ ‘
( projno POSITION(25:27) INTEGER EXTERNAL,
empno POSITION(1:4) INTEGER EXTERNAL
)
885. Can one selectively load only the records that one need? (for DBA
Look at this example, (01) is the first character, (30:37) are characters 30 to 37:
LOAD DATA
INFILE ‘mydata.dat’ BADFILE ‘mydata.bad’ DISCARDFILE ‘mydata.dis’
APPEND
INTO TABLE my_selective_table
WHEN (01) <> ‘H’ and (01) <> ‘T’ and (30:37) = ‘19991217’
(
region CONSTANT ’31’,
service_key POSITION(01:11) INTEGER EXTERNAL,
call_b_no POSITION(12:29) CHAR
)
886. Can one skip certain columns while loading data? (for DBA
One cannot use POSTION(x:y) with delimited data. Luckily, from Oracle 8i one
can specify FILLER columns. FILLER columns are used to skip columns/fields in
the load file, ignoring fields that one does not want. Look at this example: — One
cannot use POSTION(x:y) as it is stream data, there are no positional fields-the
next field begins after some delimiter, not in column X. –>
LOAD DATA
TRUNCATE INTO TABLE T1
FIELDS TERMINATED BY ‘,’
( field1,
field2 FILLER,
field3
)
887. How does one load multi-line records? (for DBA
One can create one logical record from multiple physical records using one of the
following two clauses:
. CONCATENATE: – use when SQL*Loader should combine the same number of
physical records together to form one logical record.
. CONTINUEIF – use if a condition indicates that multiple records should be
treated as one. Eg. by having a ‘#’ character in column 1.
889. How can get SQL*Loader to COMMIT only at the end of the load file?
(for DBA
One cannot, but by setting the ROWS= parameter to a large value, committing
can be reduced. Make sure you have big rollback segments ready when you use
a high value for ROWS=.
890. Can one improve the performance of SQL*Loader? (for DBA
A very simple but easily overlooked hint is not to have any indexes and/or
constraints (primary key) on your load tables during the load process. This will
significantly slow down load times even with ROWS= set to a high value.
Add the following option in the command line: DIRECT=TRUE. This will
effectively bypass most of the RDBMS processing. However, there are cases
when you can’t use direct load. Refer to chapter 8 on Oracle server Utilities
manual.
Turn off database logging by specifying the UNRECOVERABLE option. This
option can only be used with direct data loads. Run multiple load jobs
concurrently.
891. How does one use SQL*Loader to load images, sound clips and
documents? (for DBA
SQL*Loader can load data from a “primary data file”, SDF (Secondary Data file –
for loading nested tables and VARRAYs) or LOGFILE. The LOBFILE method
provides and easy way to load documents, images and audio clips into BLOB
and CLOB columns. Look at this example:
Given the following table:
CREATE TABLE image_table (
image_id NUMBER(5),
file_name VARCHAR2(30),
image_data BLOB);
Control File:
LOAD DATA
INFILE *
INTO TABLE image_table
REPLACE
FIELDS TERMINATED BY ‘,’
(
image_id INTEGER(5),
file_name CHAR(30),
image_data LOBFILE (file_name) TERMINATED BY EOF
)
BEGINDATA
001,image1.gif
002,image2.jpg
892. What is the difference between the conventional and direct path
loader? (for DBA
The conventional path loader essentially loads the data by using standard
INSERT statements. The direct path loader (DIRECT=TRUE) bypasses much of
the logic involved with that, and loads directly into the Oracle data files. More
information about the restrictions of direct path loading can be obtained from the
Utilities Users Guide.
23.Describe Oracle database’s physical and logical structure ?
Physical : Data files, Redo Log files, Control file.
Logical : Tables, Views, Tablespaces, etc.
24.Can you increase the size of a tablespace ? How ?
Yes, by adding datafiles to it.
26.What is the use of Control files ?
Contains pointers to locations of various data files, redo log files, etc.
27.What is the use of Data Dictionary ?
Used by Oracle to store information about various physical and logical Oracle
structures e.g. Tables, Tablespaces, datafiles, etc
28.What are the advantages of clusters ?
Access time reduced for joins.
80.What are the advantages of Oracle ?
Portability : Oracle is ported to more platforms than any of its competitors,
running on more than 100 hardware platforms and 20 networking protocols.
Market Presence : Oracle is by far the largest RDBMS vendor and spends more
on R & D than most of its competitors earn in total revenue. This market clout
means that you are unlikely to be left in the lurch by Oracle and there are always
lots of third party interfaces available.
Backup and Recovery : Oracle provides industrial strength support for on-line
backup and recovery and good software fault tolerence to disk failure. You can
also do point-in-time recovery.
Performance : Speed of a ‘tuned’ Oracle Database and application is quite good,
even with large databases. Oracle can manage > 100GB databases.
Multiple database support : Oracle has a superior ability to manage multiple
databases within the same transaction using a two-phase commit protocol.

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***** RAC Interview Questions *****

Q What is RAC?

RAC stands for Real Application cluster. It is a clustering solution from Oracle Corporation that ensures high availability of databases by providing instance failover, media failover features.

Q What is RAC and how is it different from non RAC databases?

RAC stands for Real Application Cluster, you have n number of instances running in their own separate nodes and based on the shared storage. Cluster is the key component and is a collection of servers operations as one unit. RAC is the best solution for high performance and high availably. Non RAC databases has single point of failure in case of hardware failure or server crash.

Q Give the usage of srvctl ?

srvctl start instance -d db_name -i “inst_name_list” [-o start_options]

srvctl stop instance -d name -i “inst_name_list” [-o stop_options]

srvctl stop instance -d orcl -i “orcl3,orcl4” -o immediate

srvctl start database -d name [-o start_options]

srvctl stop database -d name [-o stop_options]

srvctl start database -d orcl -o mount

Q Mention the Oracle RAC software components ?

Oracle RAC is composed of two or more database instances. They are composed of Memory structures and background processes same as the single instance database.Oracle RAC instances use two processes GES(Global Enqueue Service), GCS(Global Cache Service) that enable cache fusion.Oracle RAC instances are composed of following background processes:

ACMS—Atomic Controlfile to Memory Service (ACMS)
GTX0-j—Global Transaction Process
LMON—Global Enqueue Service Monitor
LMD—Global Enqueue Service Daemon
LMS—Global Cache Service Process
LCK0—Instance Enqueue Process
RMSn—Oracle RAC Management Processes (RMSn)
RSMN—Remote Slave Monitor


Q What is GRD?

GRD stands for Global Resource Directory. The GES and GCS maintains records of the statuses of each datafile and each cahed block using global resource directory.This process is referred to as cache fusion and helps in data integrity.

Q What are the different network components are in 10g RAC?

public, private, and vip components
Private interfaces is for intra node communication. VIP is all about availability of application. When a node fails then the VIP component fail over to some other node, this is the reason that all applications should based on vip components means tns entries should have vip entry in the host list

Q Give Details on ACMS:

ACMS stands for Atomic Controlfile Memory Service.In an Oracle RAC environment ACMS is an agent that ensures a distributed SGA memory update(ie)SGA updates are globally committed on success or globally aborted in event of a failure.

Q What is Cache Fusion?

Cache fusion is the mechanism to transfer the data block from memory to memory of one node to the other.If two nodes require the same block for query or update, the block must be transfered from the cache of one node to the other. RAC system must equipped with low-latency and high speed inter-connect to make it happen.

Oracle RAC is composed of two or more instances. When a block of data is read from datafile by an instance within the cluster and another instance is in need of the same block,it is easy to get the block image from the insatnce which has the block in its SGA rather than reading from the disk. To enable inter instance communication Oracle RAC makes use of interconnects. The Global Enqueue Service(GES) monitors and Instance enqueue process manages the cahce fusion.

Cache Fusion is essentially a memory-to-memory transfer of data between the nodes in the RAC environment. Before Cache Fusion, a node was required to write some of the data to disk before it could be transferred to the next node in the cluster. Cache Fusion does a straight memory-to-memory transfer. In addition, each node’s SGA has a map of what data is contained in the other node’s data caches.

The performance improvement is phenomenal. Oracle leverages the vendor’s high speed interconnects between the nodes to achieve the cache-to-cache data transfers. Before Cache Fusion, when you added a node to the cluster to increase performance of the application, it didn’t always provide you with the performance improvement that you hoped for. With Cache Fusion, you can easily cost justify the addition of another node into a RAC cluster to increase the performance of the application running on it. Oracle sales pitches describe it as ‘near linear horizontal scalability’.

Q What are the major RAC wait events?

In a RAC environment the buffer cache is global across all instances in the cluster and hence the processing differs.The most common wait events related to this are gc cr request and gc buffer busy

GC CR request :the time it takes to retrieve the data from the remote cache

Reason: RAC Traffic Using Slow Connection or Inefficient queries (poorly tuned queries will increase the amount of data blocks requested by an Oracle session. The more blocks requested typically means the more often a block will need to be read from a remote instance via the interconnect.)

GC BUFFER BUSY: It is the time the remote instance locally spends accessing the requested data block.

Q Give details on GTX0-j 

The process provides transparent support for XA global transactions in a RAC environment.The database autotunes the number of these processes based on the workload of XA global transactions.

Q Give details on LMON

This process monitors global enques and resources across the cluster and performs global enqueue recovery operations.This is called as Global Enqueue Service Monitor.

Q Give details on LMD

This process is called as global enqueue service daemon. This process manages incoming remote resource requests within each instance.

Q Give details on LMS

This process is called as Global Cache service process.This process maintains statuses of datafiles and each cahed block by recording information in a Global Resource Dectory(GRD).This process also controls the flow of messages to remote instances and manages global data block access and transmits block images between the buffer caches of different instances.This processing is a part of cache fusion feature.

Q Give details on LCK0

This process is called as Instance enqueue process.This process manages non-cache fusion resource requests such as libry and row cache requests.

Q Give details on RMSn

This process is called as Oracle RAC management process.These pocesses perform managability tasks for Oracle RAC.Tasks include creation of resources related Oracle RAC when new instances are added to the cluster.

Q How to export and import crs resources while migrating Oracle RAC to new server.

Below script generate svrctl add script for database, instance, service and 11G listeners from OCR from current RAC.
Save the result of the script and run it at new RAC.

for DBNAME in $(srvctl config database)
do

# Generate DB resource

srvctl config database -d $DBNAME -a | awk -v dbname=”$DBNAME” \
‘BEGIN { FS=”:” }
$1~/Oracle home/ || $1~/ORACLE_HOME/ {dbhome = “-o” $2}
$1~/Spfile/ || $1~/SPFILE/ {spfile = “-p” $2}
$1~/Disk Groups/ {dg = “-a” $2}
END { if (avail == “-a “) {avail = “”}; printf “%s %s %s %s %s\n”, “srvctl add database -d “, dbname, dbhome, spfile, dg }’

# Generate Instance resource

srvctl status database -d $DBNAME | awk -v dbname=”$DBNAME” \
‘$4~/running/ { printf “%s %s %s %s %s %s\n”, “srvctl add instance -d “,dbname, ” -i “, $2 ,” -n “, $7 }
$5~/running/ { printf “%s %s %s %s %s %s \n”, “srvctl add instance -d “,dbname, ” -i “, $2 ,” -n “, $8 }’

# Modify instance for 10G – ASM dependency

if [ $(echo $ORACLE_HOME | grep “1020” | wc -l ) -eq 1 ]
then
srvctl status database -d $DBNAME | awk -v dbname=”$DBNAME” \
‘$2~/1$/ { printf “%s %s %s %s %s \n”, “srvctl modify instance -d “,dbname, ” -i “, $2 ,” -s +ASM1″ }
$2~/2$/ { printf “%s %s %s %s %s \n”, “srvctl modify instance -d “,dbname, ” -i “, $2 ,” -s +ASM2″ }
$2~/3$/ { printf “%s %s %s %s %s \n”, “srvctl modify instance -d “,dbname, ” -i “, $2 ,” -s +ASM3″ }
$2~/4$/ { printf “%s %s %s %s %s \n”, “srvctl modify instance -d “,dbname, ” -i “, $2 ,” -s +ASM4″ }’
fi

echo “srvctl start database -d $DBNAME”

# Generate Service resource

snamelist=$(srvctl status service -d $DBNAME | awk ‘{print $2}’)

for sname in $snamelist
do
srvctl config service -d $DBNAME -s $sname| awk -v dbname=”$DBNAME” -v sname=$sname \
‘BEGIN { FS=”:”}
$1~/Preferred instances/ {pref = “-r” $2}
$1~/PREF/ {pref = “-r” $2; sub(/AVAIL/, “”, pref) }
$1~/Available instances/ {avail = “-a” $2}
$2~/AVAIL/ {avail = “-a” $3}
$1~/Failover type/ {ft = “-e” $2}
$1~/Failover method/ {fm = “-m” $2}
$1~/Runtime Load Balancing Goal/ {g = “-B” $2}
END { if (avail == “-a “) {avail = “”}; printf “%s %s %s %s %s %s %s %s %s %s\n”, “srvctl add service -d “,dbname, “-s “, sname, pref, avail ,ft, fm,g, “-P BASIC”}’
echo “srvctl start service -d $DBNAME -s $sname”
done
done

# Listener at 11G Home. 10G listener can’t ba added with srvctl.

srvctl config listener | awk \
‘BEGIN { FS=”:”; state = 0; }
$1~/Name/ {lname = “-l” $2; state=1};
$1~/Home/ && state == 1 {ohome = “-o” $2; state=2;}
$1~/End points/ && state == 2 {lport = “-p ” $3; state=3;}
state == 3 {if (ohome != “-o “) {printf “%s %s %s %s\n”, “srvctl add listener “, lname, ohome, lport;} state=0;}’

Q Give details on RSMN

This process is called as Remote Slave Monitor.This process manages background slave process creation andd communication on remote instances. This is a background slave process.This process performs tasks on behalf of a co-ordinating process running in another instance.

Q What components in RAC must reside in shared storage?

All datafiles, controlfiles, SPFIles, redo log files must reside on cluster-aware shred storage.

Q What is the significance of using cluster-aware shared storage in an Oracle RAC environment?

All instances of an Oracle RAC can access all the datafiles,control files, SPFILE’s, redolog files when these files are hosted out of cluster-aware shared storage which are group of shared disks.

Q Give few examples for solutions that support cluster storage

ASM(automatic storage management),raw disk devices,network file system(NFS), OCFS2 and OCFS(Oracle Cluster Fie systems).

Q What is an interconnect network?

An interconnect network is a private network that connects all of the servers in a cluster. The interconnect network uses a switch/multiple switches that only the nodes in the cluster can access.

Q How can we configure the cluster interconnect?

Configure User Datagram Protocol(UDP) on Gigabit ethernet for cluster interconnect.On unix and linux systems we use UDP and RDS(Reliable data socket) protocols to be used by Oracle Clusterware.Windows clusters use the TCP protocol.

Q Can we use crossover cables with Oracle Clusterware interconnects?

No, crossover cables are not supported with Oracle Clusterware intercnects.

Q What is the use of cluster interconnect?

Cluster interconnect is used by the Cache fusion for inter instance communication.

Q How do users connect to database in an Oracle RAC environment?

Users can access a RAC database using a client/server configuration or through one or more middle tiers ,with or without connection pooling.Users can use oracle services feature to connect to database.

Q What is the use of a service in Oracle RAC environment?

Applications should use the services feature to connect to the Oracle database.Services enable us to define rules and characteristics to control how users and applications connect to database instances.

Q What are the characteristics controlled by Oracle services feature?

The charateristics include a unique name, workload balancing and failover options,and high availability characteristics.

Q What enables the load balancing of applications in RAC?

Oracle Net Services enable the load balancing of application connections across all of the instances in an Oracle RAC database.

Q What is a virtual IP address or VIP?

A virtl IP address or VIP is an alternate IP address that the client connectins use instead of the standard public IP address. To configureVIP address, we need to reserve a spare IP address for each node, and the IP addresses must use the same subnet as the public network.

Q What is the use of VIP?

If a node fails, then the node’s VIP address fails over to another node on which the VIP address can accept TCP connections but it cannot accept Oracle connections.

Q Give situations under which VIP address failover happens

VIP addresses failover happens when the node on which the VIP address runs fails, all interfaces for the VIP address fails, all interfaces for the VIP address are disconnected from the network.

Q What is the significance of VIP address failover?

When a VIP address failover happens, Clients that attempt to connect to the VIP address receive a rapid connection refused error .They don’t have to wait for TCP connection timeout messages.

Q What are the administrative tools used for Oracle RAC environments?

Oracle RAC cluster can be administered as a single image using OEM(Enterprise Manager),SQL*PLUS,Servercontrol(SRVCTL),clusterverificationutility(cvu),DBCA,NETCA

Q How do we verify that RAC instances are running?

Issue the following query from any one node connecting through SQL*PLUS.
$connect sys/sys as sysdba
SQL>select * from V$ACTIVE_INSTANCES;
The query gives the instance number under INST_NUMBER column,host_:instancename under INST_NAME column.

Q What is FAN?

Fast application Notification as it abbreviates to FAN relates to the events related to instances,services and nodes.This is a notification mechanism that Oracle RAc uses to notify other processes about the configuration and service level information that includes service status changes such as,UP or DOWN events.Applications can respond to FAN events and take immediate action.

Q Where can we apply FAN UP and DOWN events?

FAN UP and FAN DOWN events can be applied to instances,services and nodes.
State the use of FAN events in case of a cluster configuration change?
During times of cluster configuration changes,Oracle RAC high availability framework publishes a FAN event immediately when a state change occurs in the cluster.So applications can receive FAN events and react immediately.This prevents applications from polling database and detecting a problem after such a state change.

Q Why should we have seperate homes for ASm instance?

It is a good practice to have ASM home seperate from the database hom(ORACLE_HOME).This helps in upgrading and patching ASM and the Oracle database software independent of each other.Also,we can deinstall the Oracle database software independent of the ASM instance.

Q What is the advantage of using ASM?

Having ASM is the Oracle recommended storage option for RAC databases as the ASM maximizes performance by managing the storage configuration across the disks.ASM does this by distributing the database file across all of the available storage within our cluster database environment.

Q What is rolling upgrade?

It is a new ASM feature from Database 11g.ASM instances in Oracle database 11g release(from 11.1) can be upgraded or patched using rolling upgrade feature. This enables us to patch or upgrade ASM nodes in a clustered environment without affecting database availability.During a rolling upgrade we can maintain a functional cluster while one or more of the nodes in the cluster are running in different software versions.

Q Can rolling upgrade be used to upgrade from 10g to 11g database?

No,it can be used only for Oracle database 11g releases(from 11.1).

Q State the initialization parameters that must have same value for every instance in an Oracle RAC database

Some initialization parameters are critical at the database creation time and must have same values.Their value must be specified in SPFILE or PFILE for every instance.The list of parameters that must be identical on every instance are given below:
ACTIVE_INSTANCE_COUNT
ARCHIVE_LAG_TARGET
COMPATIBLE
CLUSTER_DATABASE
CLUSTER_DATABASE_INSTANCE
CONTROL_FILES
DB_BLOCK_SIZE
DB_DOMAIN
DB_FILES
DB_NAME
DB_RECOVERY_FILE_DEST
DB_RECOVERY_FILE_DEST_SIZE
DB_UNIQUE_NAME
INSTANCE_TYPE (RDBMS or ASM)
PARALLEL_MAX_SERVERS
REMOTE_LOGIN_passWORD_FILE
UNDO_MANAGEMENT

Q What is ORA-00603: ORACLE server session terminated by fatal error or ORA-29702: error occurred in Cluster Group Service operation?

RAC node name was listed in the loopback address…

Q Can the DML_LOCKS and RESULT_CACHE_MAX_SIZE be identical on all instances?

These parameters can be identical on all instances only if these parameter values are set to zero.
What two parameters must be set at the time of starting up an ASM instance in a RAC environment?The parameters CLUSTER_DATABASE and INSTANCE_TYPE must be set.

Q Mention the components of Oracle clusterware

Oracle clusterware is made up of components like voting disk and Oracle Cluster Registry(OCR).

Q What is a CRS resource?

Oracle clusterware is used to manage high-availability operations in a cluster.Anything that Oracle Clusterware manages is known as a CRS resource.Some examples of CRS resources are database,an instance,a service,a listener,a VIP address,an application process etc.

Q What is the use of OCR?

Oracle clusterware manages CRS resources based on the configuration information of CRS resources stored in OCR(Oracle Cluster Registry).

Q How does a Oracle Clusterware manage CRS resources?

Oracle clusterware manages CRS resources based on the configuration information of CRS resources stored in OCR(Oracle Cluster Registry).

Q Name some Oracle clusterware tools and their uses?

OIFCFG – allocating and deallocating network interfaces
OCRCONFIG – Command-line tool for managing Oracle Cluster Registry
OCRDUMP – Identify the interconnect being used
CVU – Cluster verification utility to get status of CRS resources

Q What are the modes of deleting instances from ORacle Real Application cluster Databases?

We can delete instances using silent mode or interactive mode using DBCA(Database Configuration Assistant).

Q How do we remove ASM from a Oracle RAC environment?

We need to stop and delete the instance in the node first in interactive or silent mode.After that asm can be removed using srvctl tool as follows:
srvctl stop asm -n node_name
srvctl remove asm -n node_name
We can verify if ASM has been removed by issuing the following command:
srvctl config asm -n node_name

Q How do we verify that an instance has been removed from OCR after deleting an instance?

Issue the following srvctl command:
srvctl config database -d database_name
cd CRS_HOME/bin
./crs_stat

Q How do we verify an existing current backup of OCR?

We can verify the current backup of OCR using the following command : ocrconfig -showbackup
What are the performance views in an Oracle RAC environment?
We have v$ views that are instance specific. In addition we have GV$ views called as global views that has an INST_ID column of numeric data type.GV$ views obtain information from individual V$ views.
What are the types of connection load-balancing?
There are two types of connection load-balancing:server-side load balancing and client-side load balancing.

Q What is the difference between server-side and client-side connection load balancing?

Client-side balancing happens at client side where load balancing is done using listener.In case of server-side load balancing listener uses a load-balancing advisory to redirect connections to the instance providing best service.

Q What are the three greatest benefits that RAC provides??

The three main benefits are availability, scalability, and the ability to use low cost commodity hardware. RAC allows an application to scale vertically, by adding CPU, disk and memory resources to an individual server. But RAC also provides horizontal scalability, which is achieved by adding new nodes into the cluster. RAC also allows an organization to bring these resources online as they are needed. This can save a small or midsize organization a lot of money in the early stages of a project.

In a RAC environment, if a node in the cluster fails, the application continues to run on the surviving nodes contained in the cluster. If your application is configured correctly, most users won’t even know that the node they were running on became unavailable.

Q What are the major RAC wait events?

In a RAC environment the buffer cache is global across all instances in the cluster and hence the processing differs.The most common wait events related to this are gc cr request and gc buffer busy

GC CR request: the time it takes to retrieve the data from the remote cache

Reason: RAC Traffic Using Slow Connection or Inefficient queries (poorly tuned queries will increase the amount of data blocks
requested by an Oracle session. The more blocks requested typically means the more often a block will need to be read from a remote instance via the interconnect.)

GC BUFFER BUSY: It is the time the remote instance locally spends accessing the requested data block.

Q What are the different network components in Oracle 10g RAC?


We have public, private, and VIP components. Private interfaces is for intra node communication. VIP is all about availability of application. When a node fails then the VIP component will fail over to some other node, this is the reason that all applications should be based on VIP components.  This means that tns entries should have VIP entry in the host list.

Q Tune the following RAC DATABASE (DBNAME=PROD) which is 3 node RAC.

PROD1             PROD2                     PROD3
CPU 8               CPU 15                    CPU 8
32 GB RAM       12 GB RAM             16 GB RAM

What are you looking for here? What tuning information do you expect?
It is a 3 node cluster with different hardware configuration running RAC.
I would put 20% of the memory for Oracle in each node. So that would mean that the SGA is different in each of the nodes.
Also since the CPU’s are different PROD2 can have more number of max number of processes as compared to the rest of them.

But as I said this is just configuration, this is not tuning. Question is not clear.

Q Write a sample script for RMAN for the recovery if all the instance are down.(First explain the procedure how you will restore)

Bring all nodes down.
Start one Node
Restore all datafiles and archive logs.
Recover 1 Node.
Open the database.
bring other nodes up.
Confirm that all nodes are operational.

Q. Clients are performing some operation and suddenly one of the datafile is experiencing problem what do you do? The cluster is a two node one.

A. Bring the datafile offline recover the datafile.

Q. How can you connect to a specific node in a RAC environment?


A. tnsnames.ora ensure that you have INSTANCE_NAME specified in it.


Q. What happens when a DML is issued in a RAC environment, how are requests for common buffers handled in a RAC environment.

Q How to move OCR and Voting disk to new storage device?

Moving OCR
==========

You must be logged in as the root user, because root owns the OCR files. Also an ocrmirror must be in place before trying to replace the OCR device.

Make sure there is a recent backup of the OCR file before making any changes:

ocrconfig –showbackup

If there is not a recent backup copy of the OCR file, an export can be taken for the current OCR file. Use the following command to generate an export of the online OCR file:

In 10.2

ocrconfig –export -s online

In 11g

ocrconfig -manualbackup

The new OCR disk must be owned by root, must be in the oinstall group, and must have permissions set to 640. Provide at least 100 MB disk space for the OCR.

On one node as root run:

# ocrconfig -replace ocr
# ocrconfig -replace ocrmirror 

Now run ocrcheck to verify if the OCR is pointing to the new file

Moving Voting Disk
==================

Note: crsctl votedisk commands must be run as root

Shutdown the Oracle Clusterware (crsctl stop crs as root) on all nodes before making any modification to the voting disk. Determine the current voting disk location using:

crsctl query css votedisk

Take a backup of all voting disk:

dd if=voting_disk_name of=backup_file_name

To move a Voting Disk, provide the full path including file name:

crsctl delete css votedisk –force
crsctl add css votedisk –force

After modifying the voting disk, start the Oracle Clusterware stack on all nodes

# crsctl start crs

Verify the voting disk location using

crsctl query css votedisk

Q What is runfixup.sh script in Oracle Clusterware 11g release 2 installation

With Oracle Clusterware 11g release 2, Oracle Universal Installer (OUI) detects when the minimum requirements for an installation are not met, and creates shell scripts, called fixup scripts, to finish incomplete system configuration steps. If OUI detects an incomplete task, then it generates fixup scripts (runfixup.sh). You can run the fixup script after you click the Fix and Check Again Button.

The Fixup script does the following:

■ If necessary sets kernel parameters to values required for successful installation,

including:

– Shared memory parameters.

– Open file descriptor and UDP send/receive parameters.

■ Sets permissions on the Oracle Inventory (central inventory) directory.

■ Reconfigures primary and secondary group memberships for the installation

owner, if necessary, for the Oracle Inventory directory and the operating system

privileges groups.

■ Sets shell limits if necessary to required values.

Q When exactly during the installation process are clusterware components created?

After fulfilling the pre-installation requirements, the basic installation steps to follow are:

1. Invoke the Oracle Universal Installer (OUI)

2. Enter the different information for some components like:
– name of the cluster
– public and private node names
– location for OCR and Voting Disks
– network interfaces used for RAC instances
-etc.

3. After the Summary screen, OUI will start copying under the $CRS_HOME (this is the $ORACLE_HOME for Oracle Clusterware) in the local node the libraries and executables.
– here we will have the daemons and scripts init.* created and configured properly.

Oracle Clusterware is formed of several daemons, each one of which have a special function inside the stack. Daemons are executed via the init.* scripts (init.cssd, init.crsd and init.evmd).

– note that for CRS only some client libraries are recreated, but not all the executables (as for the RDBMS).

4. Later the software is propagated to the rest of the nodes in the cluster and the oraInventory is updated.

5. The installer will ask to execute root.sh on each node. Until this step the software for Oracle Clusterware is inside the $CRS_HOME.

Running root.sh will create several components outside the $CRS_HOME:

– OCR and VD will be formated.

– control files (or SCLS_SRC files ) will be created with the correct contents to start Oracle Clusterware.

These files are used to control some aspects of Oracle Clusterware like:
– enable/disable processes from the CSSD family (Eg. oprocd, oslsvmon)
– stop the daemons (ocssd.bin, crsd.bin, etc).
– prevent Oracle Clusterware from being started when the machine boots.
– etc.

– /etc/inittab will be updated and the init process is notified.

In order to start the Oracle Clusterware daemons, the init.* scripts first need to be run. These scripts are executed by the daemon init. To accomplish this some entries must be created in the file /etc/inittab.

– the different processes init.* (init.cssd, init.crsd, etc) will start the daemons (ocssd.bin, crsd.bin, etc). When all the daemons are running then we can say that the installation was successful

– On 10.2 and later, running root.sh on the last node in the cluster also will create the nodeapps (VIP, GSD and ONS). On 10.1, VIPCA is executed as part of the RAC installation.

6. After running root.sh on each node, we need to continue with the OUI session. After pressing the ‘OK’ button OUI will include the information for the public and cluster_interconnect interfaces. Also CVU (Cluster Verification Utility) will be executed.

Q What are Oracle Clusterware processes for 10g on Unix and Linux

Cluster Synchronization Services (ocssd) — Manages cluster node membership and runs as the oracle user; failure of this process results in cluster restart.

Cluster Ready Services (crsd) — The crs process manages cluster resources (which could be a database, an instance, a service, a Listener, a virtual IP (VIP) address, an application process, and so on) based on the resource’s configuration information that is stored in the OCR. This includes start, stop, monitor and failover operations. This process runs as the root user

Event manager daemon (evmd) —A background process that publishes events that crs creates.

Process Monitor Daemon (OPROCD) —This process monitor the cluster and provide I/O fencing. OPROCD performs its check, stops running, and if the wake up is beyond the expected time, then OPROCD resets the processor and reboots the node. An OPROCD failure results in Oracle Clusterware restarting the node. OPROCD uses the hangcheck timer on Linux platforms.

RACG (racgmain, racgimon) —Extends clusterware to support Oracle-specific requirements and complex resources. Runs server callout scripts when FAN events occur.

Q What are Oracle database background processes specific to RAC

•LMS—Global Cache Service Process

•LMD—Global Enqueue Service Daemon

•LMON—Global Enqueue Service Monitor

•LCK0—Instance Enqueue Process

To ensure that each Oracle RAC database instance obtains the block that it needs to satisfy a query or transaction, Oracle RAC instances use two processes, the Global Cache Service (GCS) and the Global Enqueue Service (GES). The GCS and GES maintain records of the statuses of each data file and each cached block using a Global Resource Directory (GRD). The GRD contents are distributed across all of the active instances.

Q What are Oracle Clusterware Components

Voting Disk — Oracle RAC uses the voting disk to manage cluster membership by way of a health check and arbitrates cluster ownership among the instances in case of network failures. The voting disk must reside on shared disk.

Oracle Cluster Registry (OCR) — Maintains cluster configuration information as well as configuration information about any cluster database within the cluster. The OCR must reside on shared disk that is accessible by all of the nodes in your cluster

Q How do you troubleshoot node reboot 

Please check metalink …

Note 265769.1 Troubleshooting CRS Reboots
Note.559365.1 Using Diagwait as a diagnostic to get more information for diagnosing Oracle Clusterware Node evictions.

Q How do you backup the OCR

There is an automatic backup mechanism for OCR. The default location is : $ORA_CRS_HOME\cdata\”clustername”\

To display backups :
#ocrconfig -showbackup
To restore a backup :
#ocrconfig -restore

With Oracle RAC 10g Release 2 or later, you can also use the export command:
#ocrconfig -export -s online, and use -import option to restore the contents back.
With Oracle RAC 11g Release 1, you can do a manaual backup of the OCR with the command:
# ocrconfig -manualbackup

Q How do you backup voting disk

#dd if=voting_disk_name of=backup_file_name

Q How do I identify the voting disk location 

#crsctl query css votedisk

Q How do I identify the OCR file location 

check /var/opt/oracle/ocr.loc or /etc/ocr.loc ( depends upon platform)
or
#ocrcheck

Q Is ssh required for normal Oracle RAC operation ?

“ssh” are not required for normal Oracle RAC operation. However “ssh” should be enabled for Oracle RAC and patchset installation.

Q What is SCAN?

Single Client Access Name (SCAN) is s a new Oracle Real Application Clusters (RAC) 11g Release 2 feature that provides a single name for clients to access an Oracle Database running in a cluster. The benefit is clients using SCAN do not need to change if you add or remove nodes in the cluster.

Click here for more details from Oracle

Q What is the purpose of Private Interconnect ?

Clusterware uses the private interconnect for cluster synchronization (network heartbeat) and daemon communication between the the clustered nodes. This communication is based on the TCP protocol.
RAC uses the interconnect for cache fusion (UDP) and inter-process communication (TCP). Cache Fusion is the remote memory mapping of Oracle buffers, shared between the caches of participating nodes in the cluster.

Q Why do we have a Virtual IP (VIP) in Oracle RAC?

Without using VIPs or FAN, clients connected to a node that died will often wait for a TCP timeout period (which can be up to 10 min) before getting an error. As a result, you don’t really have a good HA solution without using VIPs.
When a node fails, the VIP associated with it is automatically failed over to some other node and new node re-arps the world indicating a new MAC address for the IP. Subsequent packets sent to the VIP go to the new node, which will send error RST packets back to the clients. This results in the clients getting errors immediately.

Q What do you do if you see GC CR BLOCK LOST in top 5 Timed Events in AWR Report? 

This is most likely due to a fault in interconnect network.
Check netstat -s
if you see “fragments dropped” or “packet reassemblies failed” , Work with your system administrator find the fault with network.

Q How many nodes are supported in a RAC Database?

10g Release 2, support 100 nodes in a cluster using Oracle Clusterware, and 100 instances in a RAC database.

Q Srvctl cannot start instance, I get the following error PRKP-1001 CRS-0215, however sqlplus can start it on both nodes? How do you identify the problem?

Set the environmental variable SRVM_TRACE to true.. And start the instance with srvctl. Now you will get detailed error stack.

Q what is the purpose of the ONS daemon?

The Oracle Notification Service (ONS) daemon is an daemon started by the CRS clusterware as part of the nodeapps. There is one ons daemon started per clustered node.
The Oracle Notification Service daemon receive a subset of published clusterware events via the local evmd and racgimon clusterware daemons and forward those events to application subscribers and to the local listeners.

This in order to facilitate:

a. the FAN or Fast Application Notification feature or allowing applications to respond to database state changes.
b. the 10gR2 Load Balancing Advisory, the feature that permit load balancing accross different rac nodes dependent of the load on the different nodes. The rdbms MMON is creating an advisory for distribution of work every 30seconds and forward it via racgimon and ONS to listeners and applications.

Q How do users connect to database in an Oracle RAC environment?

Users can access a RAC database using a client/server configuration or through one or more middle tiers, with or without connection pooling. Users can use oracle services feature to connect to database.

Q What is the use of a service in Oracle RAC environment?

Applications should use the services feature to connect to the Oracle database. Services enable us to define rules and characteristics to control how users and applications connect to database instances.

Q What are the characteristics controlled by Oracle services feature?

The characteristics include a unique name, workload balancing and failover options, and high availability characteristics.

Q What is a voting disk?

A voting disk is a file that manages information about node membership.

Q What are the administrative tasks involved with voting disk?

Following administrative tasks are performed with the voting disk :

1) Backing up voting disks

2) Recovering Voting disks

3) Adding voting disks

4) Deleting voting disks

5) Moving voting disks

Q How do we backup voting disks?

1) Oracle recommends that you back up your voting disk after the initial cluster creation and after we complete any node addition or deletion procedures.

2) First, as root user, stop Oracle Clusterware (with the crsctl stop crs command) on all nodes. Then, determine the current voting disk by issuing the following command:

crsctl query votedisk css

3) Then, issue the dd or ocopy command to back up a voting disk, as appropriate.

Give the syntax of backing up voting disks:-

On Linux or UNIX systems:

dd if=voting_disk_name of=backup_file_name

where,

voting_disk_name is the name of the active voting disk

backup_file_name is the name of the file to which we want to back up the voting disk contents

On Windows systems, use the ocopy command:

ocopy voting_disk_name backup_file_name

Q What is the Oracle Recommendation for backing up voting disk?

Oracle recommends us to use the dd command to backup the voting disk with a minimum block size of 4KB.

Q How do you restore a voting disk?

To restore the backup of your voting disk, issue the dd or ocopy command for Linux and UNIX systems or ocopy for Windows systems respectively.

On Linux or UNIX systems:

dd if=backup_file_name of=voting_disk_name

On Windows systems, use the ocopy command:

ocopy backup_file_name voting_disk_name

where,

backup_file_name is the name of the voting disk backup file

voting_disk_name is the name of the active voting disk

Q How can we add and remove multiple voting disks?

If we have multiple voting disks, then we can remove the voting disks and add them back into our environment using the following commands, where path is the complete path of the location where the voting disk resides:

crsctl delete css votedisk path

crsctl add css votedisk path

Q How do we stop Oracle Clusterware?When do we stop it?

Before making any modification to the voting disk, as root user, stop Oracle Clusterware using the crsctl stop crs command on all nodes.

Q How do we add voting disk?

To add a voting disk, issue the following command as the root user, replacing the path variable with the fully qualified path name for the voting disk we want to add:

crsctl add css votedisk path -force

Q How do we move voting disks?

To move a voting disk, issue the following commands as the root user, replacing the path variable with the fully qualified path name for the voting disk we want to move:

crsctl delete css votedisk path -force

crsctl add css votedisk path -force

Q How do we remove voting disks?

To remove a voting disk, issue the following command as the root user, replacing the path variable with the fully qualified path name for the voting disk we want to remove:

crsctl delete css votedisk path -force

Q What should we do after modifying voting disks?

After modifying the voting disk, restart Oracle Clusterware using the crsctl start crs command on all nodes, and verify the voting disk location using the following command:

crsctl query css votedisk

Q When can we use -force option?

If our cluster is down, then we can include the -force option to modify the voting disk configuration, without interacting with active Oracle Clusterware daemons. However, using the -force option while any cluster node is active may corrupt our configuration.

Database Interview Questions – Basics I

Database

Q 1: What are the steps involved in database startup?
Ans: Start an Instance, Mount the database and Open the Database.

Q2: What are the steps involved in database shutdown?
Ans : Close the database ; Dismount the database and Shutdown the instance.

Q3: What is Archived Redo log?
Ans: Acrhived Redo Log consists of Redo Log files that have archived before being reused

Q4: What is a temporary segment?
Ans: Temporary segments are created by ORACLE when a sql statement needs a temporary work area to complete execution. When the statement finishes execution , the temporary segment extents are released to the system for future use.

Q5: What does a control file contain?
Ans: A control file records the physical structure of the database, database name,time stamp of database creation,max datafile limit,max redo log group,max log file members, database archive information,backup information..

Q6:What is a Tablespace?
Ans: A database is divided into Logical storage unit called tablespace. A tablespace used to grouped related logical structures together

Q7: Explain the relation ship among the database,tablespace and datafiles?
Ans: Each database logically divided in to one or more tablespaces. One or more datafiles are explicitly created for each tablespace.

Q8:What is Logical structure of the database?
Ans: Database àTablespacesàsegmentsàExtentsàOracle Blocks

Q9: What is the physical structure of the database?
Ans: Datafiles,Control File and redo log files.

Q10: What are Different types of segments?
Ans: Temp Segement, Undo Segment, Table Segment and Index Segment.

Q11: Can you name few DBMS Package names and their use?
Ans: DBMS_JOBS, DBMS_STATS,DBMS_SQLTUNE..

Q12: How Do you find whether the instance was started with PFILE or SPFILE?
Ans: Sho parameter spfile or query from v$parameter.

Q13: What Column differentiates the v$views to the gv$views and how?
Ans: The INST_ID Column which indicates the instance in a RAC environment the information came from ..

Q14: Explain an Ora -1555
Ans: You get this error when you get a snap shot too old within roolback.It can usually be solved by increasing the undo retention or increasing the size of rollbacks

Q15:What is Diffeernce between a temporary tablespace and a permanent tablespace?
Ans: A temporary tablespace is used for Sort Oprations of no sufficient space found in PGA. Permanent tablespace stores the true objects of dataase ..

Q16:How Do you add a datafile to a tablespace?
Ans: alter tablespace add datafile size ;

Q17: How Do you resize a datafile?
Ans: alter database datafile resize ;

Q18: What view Would you use to look at th size of a datafile?
Ans: dba_data_files,V$datafile

Q19: What view Would you use to determine free space in a tablespace?
Ans: dba_free_space

Q20: How can you gather statistics on a table?
Ans: The analyze command or using DBMS_STATS package.

Q21: List out the views names we can use to find about undo usage?
Ans: V$undostat,dba_undo_segs

Q22: What is view we can use to find out database locks?
Ans: v$lock

Q23: Using which view will check for session and process details?
Ans: V$session,v$process

Q24: Using which view will you find out , how much % Operation or job completed sofar it is running in database?
Ans: v$session_longops

Q25: How will you find out running job names from database?
Ans: Querying from dba_jobs,Dba_jobs_running views

Q26:How will find out Database creation time details? What is the column name?
Ans: v$database; created is column

Q27: How will you find out instance startup time?
Ans: v$instance,startup_time

Q28: How do you find archive is enabled for database?
Ans: archive log list or v$database ,log_mode Cloumn

Q29: How will you find active/inactive session count from database?
Ans: select status,count(*) from v$session group by status;

Q30: explain about temporary tablespace groups?
Ans: It is 10g new feature . it is a group of temporary tablespaces. We can get more details from dba_tablespace_groups if it is enabled.

Q31: What is undo_retention?
Ans : Time specification for undo segments hold the data ..and these reusable are reusable..

Q32: How will you find undo management is auto or manual?
Ans : Sho parameter undo_management

Q33: If your database contain 4 undo tablespaces..how will you find out which undo tablespace is used by database?
Ans: Sho parameter undo_tablespace

Q34: If you database contain 5 temporary tablespaces how will you find out what is default temporary tablespace to databse?
Ans: By querying database_properties

Q35. What is alert log file and how will you find out the location of file from database?
Ans : Sho parameter dump

UNIX:

Q36: How can you determine if an Oracle Instance is up from the Operating system level?
Ans: ps –efgrep smon/pmon

Q37: How can u find dead processes?
Ans: ps –efgrep zombie or who –d or ps –efgrep defunc

Q38: Give the command to display space usage on the UNIX File system?
Ans: df –lk or df –lh or df –k/h

Q39: Explain sar and vmstat?
Ans: sar used for to get system activity report and Vmstat reports on virtuval memory statistics for processes .

Q40: How do you find the Load average of a server?
Ans: using uptime command.

Q41: How do you find out swap usage on a server?
Ans: free –g

Q42: How will you kill a process id at OS level ?
Ans: kill -9

Q43: How will you find out the count of Oracle processes running on server?
Ans: ps –efgrep wc –l

Q44: How will you check if any Rman backup is running?
Ans: ps –efgrep rman

Q45: How will check cron schedule job details?
Ans: Crontab –l

Q46 : How will find ASM instance is running on server?
Ans : ps –efgrep +ASM

Q47 : I have a very big file at OS and I want see last 50 lines of the file only..Which command will you use?
Ans : tail -50

Q48: How can you find , file last accessed ( modified )date?
Ans : ls –l <filename)->Q49: How will you find out howmany instances are running on a server?
Ans : ps –efgrep smon (gives all instance names which are running)

Q50 : What is the command we can use to find trace of process at OS level?(means what process is doing)
And : strace –p

Oracle DBA Interview Questions – Part 2
———————————————————
 
Below are the few of Oracle database interview questions, Watch this space for more questions & answers.
 
Please provide your comments, Feedback welcome.
1) List components of an Oracle instance?
Ans:
An Oracle instance is comprised of memory structures and background processes.
The Systems Global Area (SGA) and shared pool are memory structures. The process monitor is a background process (DBWn, LGWR, ARCn, and PMON). The Oracle database consists of the physical components such as data files; redo log files, and the control file.
2)Which background process and associated database component guarantees that committed data is saved even when the changes have not been recorded in the data files?
Ans:
LGWR (log writer) and online redo log files. The log writer process writes data to the buffers when a transaction is committed. LGWR writes to the redo log files in the order of events (sequential order) in case of a failure.
3)What is the maximum number of database writer processes allowed in an Oracle instance?
Ans:
The maximum is ten. Every Oracle instance begins with only one database writer process, DBW0. Additional writer processes may be started by setting the initialization parameter DB_WRITER_PROCESSES (DBW1 through DBW9).
4)Which background process is not started by default when you start up the Oracle instance?
Ans:
ARCn. The ARCn process is available only when the archive log is running (LOG_ARCHIVE_START initialization parameter set to true). DBWn, LGWR, CKPT, SMON, and PMON are the default processes associated with all instances (start by default).
5)Describe a parallel server configuration?
Ans:
In a parallel server configuration multiple instances known as nodes can mount one database. In other words, the parallel server option lets you mount the same database for multiple instances. In a multithreaded configuration, one shared server process takes requests from multiple user processes.
6)Choose the right hierarchy, from largest to smallest, from this list of logical database structures?
Ans:
Database, tablespace, segment, extent, data blocks.
7)Which background process is responsible for writing the dirty buffers to the database files?
Ans:
The purpose if the DBWn is to write the contents of the dirty buffer to the database file.
This occurs under two circumstances – when a checkpoint occurs or when the server process searches the buffer cache for a set threshold.
8)Which component in the SGA has the dictionary cache?
Ans:
The dictionary cache is part of the shared pool. The shared pool also contains the library cache and control structures.
10)When a server process is terminated abnormally, which background process is responsible for releasing the locks held by the user?
Ans:
The process monitor (PMON) releases the locks on tables and rows held by the user during failed processes and it reclaims all resources held by the user. PMON cleans up after failed user processes.
11)What is a dirty buffer?
Ans:
A dirty buffer refers to blocks in the database buffer cache that are changed, but are not yet written to the disk.
12)If you are updating one row in a table using the ROWID in the WHERE clause (assume that the row is not already in the buffer cache), what will be the minimum amount of information read to the database buffer cache?
Ans:
The block is the minimum amount of information read/copied to the database buffer cache.
13)What happens next when a server process is not able to find enough free buffers to copy the blocks from disk?
Ans:
To reduce I/O contention, the DBWn process does not write the changed buffers immediately to the disk. They are written only when the dirty buffers reach a threshold or when there are not enough free buffers available or when the checkpoint occurs.
14)Which memory structures are shared? Name two.
Ans:
The library cache contains the shared SQL areas, private SQL areas, PL/SQL procedures, and packages, and control structures. The large pool is an optional area in the SGA.
15)When a SELECT statement is issued, which stage checks the user’s privileges?
Ans:
Parse checks the user’s privileges, syntax correctness, and the column names against the dictionary. Parse also determines the optional execution plan and finds a shared SQL area for the statement.
16)Which memory structure records all database changes made to the instance?
Ans:
The redo log files holds information on the changes made to the database data. Changes are made to the database through insert, update, delete, create, alter, or drop commands.
17)What is the minimum number of redo log files required in a database?
Ans:
The minimum number of redo log files required in a database is two because the LGWR (log writer) process writes to the redo log files in a circular manner.
18)When is the system change numbers assigned?
Ans:
System changed numbers (SCN) are assigned when a transaction is committed. The SCN is a unique number acting as an internal timestamp, used for recovery and read-consistent queries. In other words, the SCN number is assigned to the rollback statement to mark it as a transaction committed.
19)Name the parts of the database buffer pool?
Ans:
The database buffer pool consists of the keep buffer pool; recycle buffer pool, and the default buffer pool.
The keep buffer pool retains the data block in memory.
The recycle buffer pool removes the buffers from memory when it’s not needed.
The default buffer pool contains the blocks that are not assigned to the other pools.
20)List all the valid database start-up option?
Ans:
STARTUP MOUNT, STARTUP NOMOUNT, and STARTUP FORCE.
STARTUP NOMOUNT is used for creating a new database or for creating new control files. STARTUP MOUNT is used for performing specific maintenance operations such as renaming data files, enabling or disabling archive logging, renaming, adding or dropping redo log files, or for performing a full database recovery. Finally, STARTUP FORCE is used to start a database forcefully, (if you have problems starting up an instance.) STARTUP FORCE shuts down the instance if it is already running and then restarts it.
21)Which two values from the V$SESSION view are used to terminate a user session?
Ans:
The session identifier (SID) and the serial number (SERIAL #) uniquely identify each session and both are needed to kill a session. Ex. SQL > ALTER SYSTEM KILL SESSION ‘SID’,’ SERIAL #’;
22)To use operating system authentication to connect the database as an administrator, what should the value of the parameter REMOTE_LOGIN_PASSWORDFILE be set to?
Ans:
The value of the REMOTE_LOGIN_PASSWORDFILE parameter should be set to NONE to use OS authentication. To use password file authentication, the value should be either EXCLUSIVE or SHARED.
23)What information is available in the alert log files?
Ans:
The alert log store information about block corruption errors, internal errors, and the non-default initialization parameters used at instance start-up. The alert log also records information about database start-up, shutdown, archiving, recovery, tablespace modifications, rollback segment modifications, and the data file modifications.
24)Which parameter value is use to set the directory path where the alert log file is written?
Ans:
The alert log file is written in the BACKGROUND_DUMP_DEST directory. This directory also records the trace files generated by the background processes. The USER_DUMP_DEST directory has the trace files generated by user sessions. The CORE_DUMP_DEST directory is used primarily on UNIX platforms to save the core dump files. ALERT_DUMP_DEST is not a valid parameter.
25)Which SHUTDOWN option requires instance recovery when the database is started the next time?
Ans:
SHUTDOWN ABORT requires instance recovery when the database is started the next time. Oracle will also roll back uncommitted transactions during start-up. This option shuts down the instance without dismounting the database.
26)Which SHUTDOWN option will wait for the users to complete their uncommitted transactions?
Ans:
When SHUTDOWN TRANSACTIONAL is issued, Oracle waits for the users to either commit or roll back their pending transactions. Once all users have either rolled back or committed their transactions, the database is shut down. When using SHUTDOWN IMMEDIATE, the user sessions are disconnected and the changes are rolled back. SHUTDOWN NORMAL waits for the user sessions to disconnect from the database.
26)How do you make a database read-only?
Ans:
To put a database into read-only mode, you can mount the database and open the database in read-only mode. This can be accomplished in one step by using STARTUP OPEN READ ONLY.
27)Which role is created by default to administer databases?
Ans:
The DBA role is created when you create the database and is assigned to the SYS and SYSTEM users.
28)Which privilege do you need to connect to the database, if the database is started up by using STARTUP RESTRICT?
Ans:
RESTRICTED SESSION privilege is required to access a database that is in restrict mode. You can start up the database in restrict mode by using STARTUP RESTRICT, or change the database to restricted mode by using ALTER SYSTEM ENABLE RESTRICTED SESSION.
29)At which stage of the database start-up is the control file opened?
Ans:
The control file is opened when the instance mounts the database. The data files and redo log files are opened after the database is opened. When the instance is started, the background processes are started.
30)Which command will “bounce” the database-that is, shut down the database and start up the database in a single command?
Ans:
STARTUP FORCE will terminate the current instance and start up the database. It is equivalent to issuing SHUTDOWN ABORT and STARTUP OPEN.
31)When performing the command SHUTDOWN TRANASACTIONAL, what actions oracle performs internally?
Ans:
SHUTDOWN TRANSACTIONAL waits for all user transactions to complete. Once no transactions are pending, it disconnects all sessions and proceeds with the normal shutting down process. The normal shut down process performs a checkpoint, closes data files and redo log files, dismounts the database, and shuts down the instance.
32)When you issue the command ALTER SYSTEM ENABLE RESTRICTED SESSION, what happens to the users who are connected to the database?
Ans:
If you enable the RESTRICTED SESSION when users are connected, nothing happens to the already connected sessions. Future sessions are started only if the user has the RESTRICTED SESSION privilege.
33)Which view has information about users who are granted SYSDBA or SYSOPER privilege?
Ans:
A dynamic view of V$PWFILE_USERS has the username and a value of TRUE in column SYSDBA if the SYSDBA privilege is granted, or a value of TRUE in column SYSOPER if the SYSOPER privilege is granted.
34)What is the recommended configuration for control files?
Ans:
Oracle allows multiplexing of control files. If you have two control files on two disks, one disk failure will not damage both control files.
35)How many control files are required to create a database?
Ans:
You do not need any control files to create a database; the control files are created when you create a database, based on the filenames specified in the CONTROL_FILES parameter of the parameter file
36)Which environment variable or registry entry variable is used to represent the instance name?
Ans:
The Oracle_SID environment variable is used to represent the instance name. When you connect to the database without specifying a connect string, Oracle connects you to this instance.
37)Which initialization parameter cannot be changed after creating the database?
Ans:
The block size of the database cannot be changed after database creation. The database name can be changed after re-creating the control file with a new name, and the CONTROL_FILES parameter can be changed if the files are copied to a new location.
38)Which script creates the data dictionary views?
Ans:
The catalog.sql script creates the data dictionary views. The base tables for these views are created by the script sql.bsq, which is executed when you issue the CREATE DATABASE command.
39)How do you correct a procedure that has become invalid when one of the tables it is referring to was altered to drop a constraint?
Ans:
The invalid procedure, trigger, package, or view can be recompiled by using the ALTER COMPILE command.
40)How many data files can be specified in the DATAFILE clause when creating a database?
Ans:
You can specify more than one data file; the files will be used for the SYSTEM tablespace. The files specified cannot exceed the number of data files specified in the MAXDATAFILES clause.
41)Who owns the data dictionary?
Ans:
The SYS user owns the data dictionary. The SYS and SYSTEM users are created when the database is created.
42)
What is the default password for the SYS user?
The default password for the SYS user is CHANGE_ON_INSTALL, and for SYSTEM it is MANAGER. You should change these passwords once the database is created.
43)What is the prefix for dynamic performance views?
Ans:
The dynamic performance views have a prefix of V$. The actual views have the prefix of V_$, and the synonyms have a V$ prefix. The views are called dynamic performance views because they are continuously updated while the database is open and in use, and their contents related primarily to performance.
44)What piece of information is not available in the control file?
Ans:
The instance name is not available. The control files include the following:
Database name the control file belongs to, database creation timestamp, data files, redo log files, tablespace names, current log sequence number, most recent checkpoint information, and Recovery Manager’s backup information.
45)When you create a control file, the database has to be:
Ans:
Not mounted.
46)Which data dictionary view provides the names of the control files?
V$CONTROLFILES shows the names of the control files.
47)The initialization parameter file has LOG_CHECKPOINT_INTERVAL = 60; what does this mean?
Ans:
LOG_CHECKPOINT_INTERVAL ensures that no more than a specified number of redo log blocks (OS blocks) need to be read during instance recovery. LOG_CHECKPOINT_TIMEOUT ensures that no more than a specified number of seconds worth of redo log blocks need to be read during instance recovery.
48) What will happen if ARCn could not write to a mandatory archive destination?
Ans:
Oracle will write a message to the alert file and all database operations will be stopped. Database operation resumes automatically after successfully writing the archived log file. If the archive destination becomes full you can make room for archives either by deleting the archive log files after copying them to a different location, or by changing the parameter to point to a different archive location.
49What are the valid status codes in the V$LOGFILE view?
Ans:
Valid status codes V$LOGFILE views include STALE, INVALID, DELETED, or the status can be blank. STALE means the file contents are incomplete; INVALID means the file is not accessible; DELETED means the file is no longer used; and blank status means the file is in use.
50)If you have two redo log groups with four members each, how many disks does Oracle recommend to keep the redo log files?
Ans:
You should keep a minimum of two redo log groups, with a recommended two members in each group. Oracle recommends that you keep each member of a redo log group on a different disk. The maximum number of redo log groups is determined by the MAXLOGFILES database parameter. The MAXLOGMEMBERS database parameter specifies the maximum number of members per group.
51)When does the SMON process automatically coalesce the tablespaces?
Ans:
When the PCTINCREASE default storage of the tablespace is set to 0. You can manually coalesce a tablespace by using ALTER TABLESPACE COALESCE.
52)How would you drop a tablespace if the tablespace were not empty?
Ans:
Use DROP TABLESPACE INCLUDING CONTENTS.
The INCLUDING CONTENTS clause is used to drop a tablespace that is not empty. Oracle does not remove the data files that belong to the tablespace; you need to do it manually using an OS command. Oracle updates only the control file.
53)Which command is used to enable the auto-extensible feature for a file, if the file is already part of a tablespace?
Ans:
To enable auto=extension, use ALTER DATABASE DATAFILE AUTOEXTEND ON NEXT MAXSIZE .
54)How would you determine how much sort space is used by a user session?
Ans:
The V$SORT_USAGE shows the active sorts in the database; it shows the space used, username, SQL address, and hash value. It also provides the number of EXTENTS and number of BLOCKS used by each sort session, and the username. The V$SORT can be joined with V$SESSION or V$SQL to obtain more information on the session or the SQL statement causing the sort.
55)When a table is updated, where is the before image information (which can be used for undoing the changes) stored?
Ans:
Rollback segment. Before any DML operation, the undo information (before-image of data) is stored in the rollback segments. This information is used to undo the changes and to provide a read-consistent view of the data.
56)Which parameter specifies the number of transaction slots in a data block?
Ans:
INITRANS specifies the number of transaction slots in a data block. A transaction slot is used by Oracle when the data block is being modified. INITRANS reserves space for the transactions in the block.
57)Which data dictionary view would you query to see the free extents in a tablespace?
Ans:
DBA_FREE_SPACE shows the free extents in a tablespace. DBA_EXTENTS shows all the extents that are allocated to a segment.
58)Which portion of the data block stores information about the table having rows in this block?
Ans:
Row Data. The table directory portion of the block stores information about the table having rows in the block. The row directory stores information such as row address and size of the actual rows stored in the row data area.

UNIX Interview Questions/FAQs for Oracle DBAs

1. What’s the difference between soft link and hard link?
Ans:
A symbolic (soft) linked file and the targeted file can be located on the same or different file system while for a hard link they must be located on the same file system, because they share same inode number and an inode table is unique to a file system, both must be on the same file system.

2. How you will read a file from shell script?
Ans:
while read line
do
echo $line
done < file_name

3. What’s the use of umask?
Will decide the default permissions for files.

4. What is crontab and what are the arguments?
Ans:
The entries have the following elements:
field             allowed values
—–             ————–
minute            0-59
hour                0-23
day of month   1-31
month             1-12
day of week     0-7 (both 0 and 7 are Sunday)
user                 Valid OS user
command         Valid command or script

? ? ? ? ? command
|  | |  | |_________day of the week (0-6, 0=Sunday)
|  | |  |___________month (1-12)
|  | |_____________day of the month (1-31)
|  |_______________hour (0-23)
|_________________minute (0-59)

5. How to find operating system (OS) version?
Ans:
uname –a

6. How to find out the run level of the user?
Ans:
uname –r

7. How to delete 7 days old trace files?
Ans:
find ./trace –name *.trc –mtime +7 –exec rm {} ;

8. How to get 10th line of a file (by using grep)?

9. (In Solaris) how to find out whether it’s 32bit or 64bit?

10. What is paging?

11. What is top command?
Ans:
top is a operating system command, it will display top processes which are taking high cpu and memory.

12. How to find out the status of last command executed?
Ans:
$?

13. How to find out number of arguments passed to a shell script?
Ans:
$#

14. What is the default value of umask?
Ans:
022

15. How to add user in Solaris/Linux?
Ans:
useradd command

Oracle RMAN Interview Questions/FAQs

1. Difference between catalog and nocatalog?

2. Difference between using recovery catalog and control file?
When new incarnation happens, the old backup information in control file will be lost. It will be preserved in recovery catalog.
In recovery catalog, we can store scripts.
Recovery catalog is central and can have information of many databases.

3. Can we use same target database as catalog?
No. The recovery catalog should not reside in the target database (database to be backed up), because the database can’t be recovered in the mounted state.

4. How do u know how much RMAN task has been completed?
By querying v$rman_status or v$session_longops

5. From where list & report commands will get input?

6. Command to delete archive logs older than 7days?
RMAN> delete archivelog all completed before sysdate-7;

7. How many days backup, by default RMAN stores?

8. What is the use of crosscheck command in RMAN?
Crosscheck will be useful to check whether the catalog information is intact with OS level information.

9. What are the differences between crosscheck and validate commands?

10. Which is one is good, differential (incremental) backup or cumulative (incremental) backup?
A differential backup, which backs up all blocks changed after the most recent incremental backup at level 1 or 0
A cumulative backup, which backs up all blocks changed after the most recent incremental backup at level 0

11. What is Level 0, Level 1 backup?
A level 0 incremental backup, which is the base for subsequent incremental backups, copies all blocks containing data, backing the datafile up into a backup set just as a full backup would. A level 1 incremental backup can be either of the following types:
A differential backup, which backs up all blocks changed after the most recent incremental backup at level 1 or 0
A cumulative backup, which backs up all blocks changed after the most recent incremental backup at level 0

12. Can we perform level 1 backup without level 0 backup?
If no level 0 backup is available, then the behavior depends upon the compatibility mode setting. If compatibility < 10.0.0, RMAN generates a level 0 backup of the file contents at the time of the backup. If compatibility is >= 10.0.0, RMAN copies all blocks changed since the file was created, and stores the results as a level 1 backup. In other words, the SCN at the time the incremental backup is taken is the file creation SCN.

13. Will RMAN put the database/tablespace/datafile in backup mode?
Nope.

14. What is snapshot control file?

15. What is the difference between backup set and backup piece?
Backup set is logical and backup piece is physical.

16. RMAN command to backup for creating standby database?
RMAN> duplicate target database to standby database ….

17. How to do cloning by using RMAN?
RMAN> duplicate target database …

18. You loss one datafile and DB is running in ARCHIVELOG mode. You have full database backup of 1 week/day old and don’t have backup of this (newly created) datafile. How do you restore/recover file?
create the datafile and recover that datafile.
SQL> alter database create datafile ‘…path..’ size n;
RMAN> recover datafile file_id;

19. What is obsolete backup & expired backup?
A status of “expired” means that the backup piece or backup set is not found in the backup destination.
A status of “obsolete” means the backup piece is still available, but it is no longer needed. The backup piece is no longer needed since RMAN has been configured to no longer need this piece after so many days have elapsed, or so many backups have been performed.

20. What is the difference between hot backup & RMAN backup?
For hot backup, we have to put database in begin backup mode, then take backup.
RMAN won’t put database in backup mode.

21. How to put manual/user-managed backup in RMAN (recovery catalog)?
By using catalog command.
RMAN> CATALOG START WITH ‘/tmp/backup.ctl’;

22. What are new features in Oracle 11g RMAN?

23. What is the difference between auxiliary channel and maintenance channel?

Oracle DBA Interview Questions/FAQs

1. What is an instance?
SGA + background processes.

2. What is SGA?
System/Shared Global Area.

3. What is PGA (or) what is pga_aggregate_target?
Programmable Global Area.

4. What are new memory parameters in Oracle 10g?
SGA_TARGET PGA_TARGET

5. What are new memory parameters in Oracle 11g?
MEMORY_TARGET

6. What are the mandatory background processes?
DBWR LGWR SMON PMON CKPT RECO.

7. What are the optional background processes?
ARCH, MMAN, MMNL, MMON, CTWR, ASMB, RBAL, ARBx etc.

8. What are the new background processes in Oracle 10g?
MMAN MMON MMNL CTWR ASMB RBAL ARBx

9. What are the new features in Oracle 9i?
http://satya-dba.blogspot.com/2009/01/whats-new-in-9i.html

10. What are the new features in Oracle 10g?
http://satya-dba.blogspot.com/2009/01/whats-new-in-10g.html

11. What are the new features in Oracle 11g?
http://satya-dba.blogspot.com/2009/01/whats-new-in-11g.html

12. What are the new features in Oracle 11g R2?
http://satya-dba.blogspot.com/2009/09/whats-new-in-11g-release-2.html

13. What are the new features in Oracle 12c?
http://satya-dba.blogspot.com/2012/10/new-features-in-oracle-database-12c.html

14. What process will get data from datafiles to DB cache?
Server process

15. What background process will writes data to datafiles?
DBWR

16. What background process will write undo data?
DBWR

17. What are physical components of Oracle database?
Oracle database is comprised of three types of files. One or more datafiles, two or more redo log files, and one or more control files. Password file and parameter file also come under physical components.

18. What are logical components of Oracle database?
Blocks, Extents, Segments, Tablespaces.

19. What is segment space management?
LMTS and DMTS.

20. What is extent management?
Auto and Manual.

21. What are the differences between LMTS and DMTS?
Tablespaces that record extent allocation in the dictionary are called dictionary managed tablespaces, and tablespaces that record extent allocation in the tablespace header are called locally managed tablespaces.

21. What is a datafile?
Every Oracle database has one or more physical datafiles. Datafiles contain all the database data. The data of logical database structures such as tables and indexes is physically stored in the datafiles allocated for a database.

22. What are the contents of control file?
Database name, SCN, LSN, datafile locations, redolog locations, archive mode, DB Creation Time, RMAN Backup & Recovery Details, Flashback mode.

23. What is the use of redo log files?

24. What are the uses of undo tablespace or redo segments?

25. How undo tablespace can guarantee retain of required undo data?
Alter tablespace undo_ts retention guarantee;

26. What is ORA-01555 – snapshot too old error and how do you avoid it?

27. What is the use/size of temporary tablespace?

28. What is the use of password file?

29. How to create password file?
$ orapwd file=orapwSID password=sys_password force=y nosysdba=y

30. How many types of indexes are there?
Clustered and Non-Clustered

1.B-Tree index
2.Bitmap index
3.Unique index
4.Function based index

Implicit index and explicit index.
Explicit indexes are again of many types like simple index, unique index, Bitmap index, Functional index, Organisational index, cluster index.

31. What is bitmap index & when it’ll be used?
Bitmap indexes are preferred in Data warehousing environment.
Preferred when cardinality is low.

32. What is B-tree index & when it’ll be used?
B-tree indexes are preferred in OLTP environment.
Preferred when cardinality is high.

33. How you will find out fragmentation of index?
AUTO_SPACE_ADVISOR_JOB will run in daily maintenance window and report fragmented indexes/Tables.

analyze index validate structure;
This populates the table ‘index_stats’. It should be noted that this table contains only one row and therefore only one index can be analysed at a time.

An index should be considered for rebuilding under any of the following conditions:
* The percentage of deleted rows exceeds 30% of the total, i.e. if del_lf_rows / lf_rows > 0.3.
* If the ‘HEIGHT’ is greater than 4.
* If the number of rows in the index (‘LF_ROWS’) is significantly smaller than ‘LF_BLKS’ this can indicate a large number of deletes, indicating that the index should be rebuilt.

34. What is the difference between delete and truncate?
Truncate will release the space. Delete won’t.
Delete can be used to delete some records. Truncate can’t.
Delete can be rollbacked.
Delete will generate undo (Delete command will log the data changes in the log file where as the truncate will simply remove the data without it. Hence data removed by Delete command can be rolled back but not the data removed by TRUNCATE).
Truncate is a DDL statement whereas DELETE is a DML statement.
Truncate is faster than delete.

35. What’s the difference between a primary key and a unique key?
Both primary key and unique enforce uniqueness of the column on which they are defined. But by default primary key creates a clustered index on the column, where unique key creates a nonclustered index by default. Primary key doesn’t allow NULLs, but unique key allows one NULL only.

36. What is the difference between schema and user?
Schema is collection of user’s objects.

37. What is the difference between SYSDBA, SYSOPER and SYSASM?
SYSOPER can’t create and drop database.
SYSOPER can’t do incomplete recovery.
SYSOPER can’t change character set.
SYSOPER can’t CREATE DISKGROUP, ADD/DROP/RESIZE DISK

SYSASM can do anything SYSDBA can do.

38. What is the difference between SYS and SYSTEM?
SYSTEM can’t shutdown the database.
SYSTEM can’t create another SYSTEM, but SYS can create another SYS or SYSTEM.

39. How to improve sqlldr (SQL*Loader) performance?

40. What is the difference between view and materialized view?
View is logical, will store only the query, and will always gets latest data.
Mview is physical, will store the data, and may not get latest data.

41. What are materialized view refresh types and which is default?
Complete, fast, force(default)

42. How fast refresh happens?

43. How to find out when was a materialized view refreshed?
Query dba_mviews or dba_mview_analysis or dba_mview_refresh_times
SQL> select MVIEW_NAME, to_char(LAST_REFRESH_DATE,’YYYY-MM-DD HH24:MI:SS’) from dba_mviews;
(or)
SQL> select NAME, to_char(LAST_REFRESH,’YYYY-MM-DD HH24:MI:SS’) from dba_mview_refresh_times;
(or)
SQL> select MVIEW_NAME, to_char(LAST_REFRESH_DATE,’YYYY-MM-DD HH24:MI:SS’) from dba_mview_analysis;

44. What is materialized view log (type)?

45. What is atomic refresh in mviews?
From Oracle 10g, complete refresh of single materialized view can do delete instead of truncate. To force the refresh to do truncate instead of delete, parameter ATOMIC_REFRESH must be set to false.

ATOMIC_REFRESH = FALSE, mview will be truncated and whole data will be inserted. The refresh will go faster, and no undo will be generated.
ATOMIC_REFRESH = TRUE (default), mview will be deleted and whole data will be inserted. Undo will be generated. We will have access at all times even while it is being refreshed.

SQL> EXEC DBMS_MVIEW.REFRESH(‘mv_emp’, ‘C’, atomic_refresh=FALSE);

46. How to find out whether database/tablespace/datafile is in backup mode or not?
Query V$BACKUP view.

47. What is row chaining?
If the row is too large to fit into an empty data block in this case the oracle stores the data for the row in a chain of one or more data blocks. Can occur when the row is inserted.

48. What is row migration?
An update statement increases the amount of data in a row so that the row no longer fits in its data blocks. Now the oracle tries to find another free block with enough space to hold the entire row if such a block is available oracle moves entire row to new block.

49. What are different types of partitions?
With Oracle8, Range partitioning (on single column) was introduced.
With Oracle8i, Hash and Composite(Range-Hash) partitioning was introduced.
With Oracle9i, List partitioning and Composite(Range-List) partitioning was introduced.
With Oracle 11g, Interval partitioning, REFerence partitioning, Virtual column based partitioning, System partitioning and Composite partitioning [Range-Range, List-List, List-Range, List-Hash, Interval-Range, Interval-List, Interval-Interval] was introduced.

50. What is local partitioned index and global partitioned index?
A local index is an index on a partitioned table which is partitioned in the exact same manner as the underlying partitioned table. Each partition of a local index corresponds to one and only one partition of the underlying table.
A global partitioned index is an index on a partitioned or non partitioned tables which are partitioned using a different partitioning key from the table and can have different number of partitions. Global partitioned indexes can only be partitioned using range partitioning.

51. How you will recover if you lost one/all control file(s)?

52. Why more archivelogs are generated, when database is begin backup mode?
During begin backup mode datafile headers get freezed and as result row information cannot be retrieved as a result the entire block is copied to redo logs as a result more redo generated and more log switch and in turn more archive logs. Normally only deltas (change vectors) are logged to the redo logs. When in backup mode, Oracle will write complete changed blocks to the redo log files.

Mainly to overcome fractured blocks. Most of the cases Oracle block size is equal to or a multiple of the operating system block size.

e.g. Consider Oracle blocksize is 2k and OSBlocksize is 4k. so each OS Block is comprised of 2 Oracle Blocks. Now you are doing an update when your db is in backup mode. An Oracle Block is updating and at the same time backup is happening on the OS block which is having this particular DB block. Backup will not be consistent since the one part of the block is being updated and at the same time it is copied to the backup location. In this case we will have a fractured block, so as to avoid this Oracle will copy the whole OS block to redo logfile which can be used for recovery. Because of this redo generation is more.

53. What UNIX parameters you will set while Oracle installation?
shmmax, shmmni, shmall, sem,

54. What is the use of inittrans and maxtrans in table definition?

55. What are differences between dbms_job and dbms_schedular?
Through dbms_schedular we can schedule OS level jobs also.

56. What are differences between dbms_schedular and cron jobs?
Through dbms_schedular we can schedule database jobs, through cron we can’t set.

57. Difference between CPU & PSU patches?
CPU – Critical Patch Update – includes only Security related patches.
PSU – Patch Set Update – includes CPU + other patches deemed important enough to be released prior to a minor (or major) version release.

58. What you will do if (local) inventory corrupted [or] opatch lsinventory is giving error?

59. What are the entries/location of oraInst.loc?
/etc/oraInst.loc is pointer to central/local Oracle Inventory.

60. What is the difference between central/global inventory and local inventory?

61. What is the use of root.sh & oraInstRoot.sh?
Ans:
Changes ownership & permissions of oraInventory
Creating oratab file in the /etc directory
In RAC, starts the clusterware stack

62. What is transportable tablespace (and across platforms)?

63. How can you transport tablespaces across platforms with different endian formats?
Ans:
RMAN

64. What is xtss (cross platform transportable tablespace)?

65. What is the difference between restore point & guaranteed restore point?

66. What is the difference between 10g/11g OEM Grid control and 12c Cloud control?

67. What are the components of Grid control?
Ans:
OMS (Oracle Management Server)
OMR (Oracle Management Repository)
OEM Agent

68. What are the new features of 12c Cloud control?

69. How to find if your Oracle database is 32 bit or 64 bit?
Ans:
execute the command “file $ORACLE_HOME/bin/oracle”, you should see output like /u01/db/bin/oracle: ELF 64-bit MSB executable SPARCV9 Version 1

means you are on 64 bit oracle.

If your oracle is 32 bit you should see output like below
oracle: ELF 32-bit MSB executable SPARC Version 1

70. How to find opatch Version ?
Ans:
opatch is utility to apply database patch, In order to find opatch version execute”$ORACLE_HOME/OPatch/opatch version”

Oracle Data Guard Interview Questions/FAQs

1. How to setup Data Guard?

2. What are different types of modes in Data Guard and which is default?
Maximum performance:
This is the default protection mode. It provides the highest level of data protection that is possible without affecting the performance of a primary database. This is accomplished by allowing transactions to commit as soon as all redo data generated by those transactions has been written to the online log.

Maximum protection:
This protection mode ensures that no data loss will occur if the primary database fails. To provide this level of protection, the redo data needed to recover a transaction must be written to both the online redo log and to at least one standby database before the transaction commits. To ensure that data loss cannot occur, the primary database will shut down, rather than continue processing transactions.

Maximum availability:
This protection mode provides the highest level of data protection that is possible without compromising the availability of a primary database. Transactions do not commit until all redo data needed to recover those transactions has been written to the online redo log and to at least one standby database.

3. How many standby databases we can create (in 10g/11g)?
Till Oracle 10g, 9 standby databases are supported.
From Oracle 11g R2, we can create 30 standby databases.

4. What are the parameters we’ve to set in primary/standby for Data Guard?

5. What is the use of fal_server & fal_client, is it mandatory to set these?

6. What are differences between physical, logical, snapshot standby and ADG (or) what are different types of standby databases?
Physical standby – in mount state, MRP will apply archives
ADG – in READ ONLY state, MRP will apply archives
Logical standby – in READ ONLY state, LSP will run
Snapshot standby databases – Physical standby database can be converted to snapshot standby database, which will be in READ WRITE mode, can do any kind of testing, then we can convert back snapshot standby database to physical standby database and start MRP which will apply all pending archives.

7. How to find out backlog of standby?
select round((sysdate – a.NEXT_TIME)*24*60) as “Backlog”,m.SEQUENCE#-1 “Seq Applied”,m.process, m.status
from v$archived_log a, (select process,SEQUENCE#, status from v$managed_standby where process like ‘%MRP%’)m where a.SEQUENCE#=(m.SEQUENCE#-1);

8. If you didn’t have access to the standby database and you wanted to find out what error has occurred in a data guard configuration, what view would you check in the primary database to check the error message?
You can check the v$dataguard_status view.
select message from v$dataguard_status;

9. How can u recover standby which far behind from primary (or) without archive logs how can we make standby sync?
By using RMAN incremental backup.

10. What is snapshot standby (or) How can we give a physical standby to user in READ WRITE mode and let him do updates and revert back to standby?
Till Oralce 10g, create guaranteed restore point, open in read write, let him do updates, flashback to restore point, start MRP.
From Oracle 11g, convert physical standby to snapshot standby, let him do updates, convert to physical standby, start MRP.

11. What are new features in 11g Data Guard?

12. What are the uses of standby redo log files?

13. What is dg_config?

14. What is RTA (real time apply) mode MRP?

15. What is the difference between normal MRP (managed apply) and RTA MRP (real time apply)?

16. What are various parameters in log_archive_dest and it’s use?

17. What is the difference between SYNC/ASYNC, LGWR/ARCH, and AFFIRM/NOAFFIRM?

18. What is Data Guard broker (or) what is the use of dgmgrl?

19. What is StaticConnectIdentifier property used for?

20. What is failover/switchover (or) what is the difference between failover & switchover?

21. What are the background processes involved in Data Guard?
MRP, LSP,

Oracle ASM Interview Questions/FAQs

1. What is the use of ASM (or) Why ASM preferred over filesystem?
ASM provides striping and mirroring.

2. What are the init parameters related to ASM?
INSTANCE_TYPE = ASM
ASM_POWER_LIMIT = 11
ASM_DISKSTRING = ‘/dev/rdsk/*s2’, ‘/dev/rdsk/c1*’
ASM_DISKGROUPS = DG_DATA, DG_FRA

3. What is rebalancing (or) what is the use of ASM_POWER_LIMIT?
ASM_POWER_LIMIT is dynamic parameter, which will be useful for rebalancing the data across disks.
Value can be 1(lowest) to 11 (highest).

4. What are different types of redundancies in ASM & explain?
External redundancy,
Normal redundancy,
High redundancy.

5. How to copy file to/from ASM from/to filesystem?
By using ASMCMD cp command

6. How to find out the databases, which are using the ASM instance?
ASMCMD> lsct
SQL> select DB_NAME from V$ASM_CLIENT;

7. What are different types of stripings in ASM & their differences?
Fine-grained striping
Coarse-grained striping
lsdg
select NAME,ALLOCATION_UNIT_SIZE from v$asm_diskgroup;

8. What is allocation unit and what is default value of au_size and how to change?
Every ASM disk is divided into allocation units (AU). An AU is the fundamental unit of allocation within a disk group. A file extent consists of one or more AU. An ASM file consists of one or more file extents.
CREATE DISKGROUP disk_group_2 EXTERNAL REDUNDANCY DISK ‘/dev/sde1’ ATRRIBUTE ‘au_size’ = ’32M’;

9. What are the background processes in ASM?

10. What process does the rebalancing?
RBAL, ARBn

11. How to add/remove disk to/from diskgroup?

Oracle DBA interview questions

Interview FAQ2

1. Explain the difference between a hot backup and a cold backup and the benefits

associated with each.

A hot backup is basically taking a backup of the database while it is still up and running

and it must be in archive log mode. A cold backup is taking a backup of the database

while it is shut down and does not require being in archive log mode. The benefit of

taking a hot backup is that the database is still available for use while the backup is

occurring and you can recover the database to any ball in time. The benefit of taking a

cold backup is that it is typically easier to administer the backup and recovery process.

In addition, since you are taking cold backups the database does not require being in

archive log mode and thus there will be a slight performance gain as the database is not

cutting archive logs to disk.

2. You have just had to restore from backup and do not have any control files. How

would you go about bringing up this database?

I would create a text based backup control file, stipulating where on disk all the data

files where and then issue the recover command with the using backup control file

clause.

3. How do you switch from an init.ora file to a spfile?

Issue the create spfile from pfile command.

4. Explain the difference between a data block, an extent and a segment.

A data block is the smallest unit of logical storage for a database object. As objects

grow they take chunks of additional storage that are composed of contiguous data

blocks. These groupings of contiguous data blocks are called extents. All the extents

that an object takes when grouped together are considered the segment of the database

object.

5. Give two examples of how you might determine the structure of the table DEPT.

Use the describe command or use the dbms_metadata.get_ddl package.

6. Where would you look for errors from the database engine?

In the alert log.

7. Compare and contrast TRUNCATE and DELETE for a table.

Both the truncate and delete command have the desired outcome of getting rid of all the

rows in a table. The difference between the two is that the truncate command is a DDL

operation and just moves the high water mark and produces a now rollback. The delete

command, on the other hand, is a DML operation, which will produce a rollback and

thus take longer to complete.

8. Give the reasoning behind using an index.

Faster access to data blocks in a table.

9. Give the two types of tables involved in producing a star schema and the type of

data they hold.

Fact tables and dimension tables. A fact table contains measurements while dimension

tables will contain data that will help describe the fact tables.

10. What type of index should you use on a fact table?

A Bitmap index.

11. Give two examples of referential integrity constraints.

A primary key and a foreign key.

12. A table is classified as a parent table and you want to drop and re-create it. How

would you do this without affecting the children tables?

Disable the foreign key constraint to the parent, drop the table, re-create the table,

enable the foreign key constraint.

13. Explain the difference between ARCHIVELOG mode and NOARCHIVELOG mode and the benefits and disadvantages to each.

ARCHIVELOG mode is a mode that you can put the database in for creating a backup

of all transactions that have occurred in the database so that you can recover to any ball

in time. NOARCHIVELOG mode is basically the absence of ARCHIVELOG mode and

has the disadvantage of not being able to recover to any ball in time.

NOARCHIVELOG mode does have the advantage of not having to write transactions

to an archive log and thus increases the performance of the database slightly.

14. What command would you use to create a backup control file?

Alter database backup control file to trace.

15. Give the stages of instance startup to a usable state where normal users may access it.

STARTUP NOMOUNT – Instance startup

STARTUP MOUNT – The database is mounted

STARTUP OPEN – The database is opened

16. What column differentiates the V$ views to the GV$ views and how?

The INST_ID column which indicates the instance in a RAC environment the

information came from.

17. How would you go about generating an EXPLAIN plan?

Create a plan table with utlxplan.sql.

Use the explain plan set statement_id = ‘tst1′ into plan_table for a SQL statement

Look at the explain plan with utlxplp.sql or utlxpls.sql

18. How would you go about increasing the buffer cache hit ratio?

Use the buffer cache advisory over a given workload and then query the

v$db_cache_advice table. If a change was necessary then I would use the alter system

set db_cache_size command.

19. Explain an ORA-01555

You get this error when you get a snapshot too old within rollback. It can usually be

solved by increasing the undo retention or increasing the size of rollbacks. You should

also look at the logic involved in the application getting the error message.

20. Explain the difference between $ORACLE_HOME and $ORACLE_BASE.

ORACLE_BASE is the root directory for oracle. ORACLE_HOME located beneath

ORACLE_BASE is where the oracle products reside.

1. Describe the difference between a procedure, function and anonymous pl/sql

block.

Candidate should mention use of DECLARE statement, a function must return a value

while a procedure doesn?t have to.

2. What is a mutating table error and how can you get around it?

This happens with triggers. It occurs because the trigger is trying to update a row it is

currently using. The usual fix involves either use of views or temporary tables so the

database is selecting from one while updating the other.

3. Describe the use of %ROWTYPE and %TYPE in PL/SQL

Expected answer: %ROWTYPE allows you to associate a variable with an entire table

row. The %TYPE associates a variable with a single column type.

4. 4What packages (if any) has Oracle provided for use by developers?

Expected answer: Oracle provides the DBMS_ series of packages. There are many

which developers should be aware of such as DBMS_SQL, DBMS_PIPE,

DBMS_TRANSACTION, DBMS_LOCK, DBMS_ALERT, DBMS_OUTPUT,

DBMS_JOB, DBMS_UTILITY, DBMS_DDL, UTL_FILE. If they can mention a few

of these and describe how they used them, even better. If they include the SQL routines

provided by Oracle, great, but not really what was asked.

5. Describe the use of PL/SQL tables

Expected answer: PL/SQL tables are scalar arrays that can be referenced by a binary

integer. They can be used to hold values for use in later queries or calculations. In

Oracle 8 they will be able to be of the %ROWTYPE designation, or RECORD.

6. When is a declare statement needed ?

The DECLARE statement is used in PL/SQL anonymous blocks such as with stand

alone, non-stored PL/SQL procedures. It must come first in a PL/SQL stand alone file if

it is used.

7. In what order should a open/fetch/loop set of commands in a PL/SQL block be

implemented if you use the %NOTFOUND cursor variable in the exit when statement? Why?

Expected answer: OPEN then FETCH then LOOP followed by the exit when. If not

specified in this order will result in the final return being done twice because of the way

the %NOTFOUND is handled by PL/SQL.

8. What are SQLCODE and SQLERRM and why are they important for PL/SQL

developers?

Expected answer: SQLCODE returns the value of the error number for the last error

encountered. The SQLERRM returns the actual error message for the last error

encountered. They can be used in exception handling to report, or, store in an error log

table, the error that occurred in the code. These are especially useful for the WHEN

OTHERS exception.

9. How can you find within a PL/SQL block, if a cursor is open?

Expected answer: Use the %ISOPEN cursor status variable.

10. How can you generate debugging output from PL/SQL?

Expected answer: Use the DBMS_OUTPUT package. Another possible method is to

just use the SHOW ERROR command, but this only shows errors. The

DBMS_OUTPUT package can be used to show intermediate results from loops and the

status of variables as the procedure is executed. The new package UTL_FILE can also

be used.

11. What are the types of triggers?

Expected Answer: There are 12 types of triggers in PL/SQL that consist of

combinations of the BEFORE, AFTER, ROW, TABLE, INSERT, UPDATE, DELETE

and ALL key words:

BEFORE ALL ROW INSERT

AFTER ALL ROW INSERT

BEFORE INSERT

AFTER INSERT etc.

1. Give one method for transferring a table from one schema to another:

There are several possible methods, export-import, CREATE TABLE… AS SELECT, or

COPY.

2. What is the purpose of the IMPORT option IGNORE? What is it?s default setting

The IMPORT IGNORE option tells import to ignore “already exists” errors. If it is not

specified the tables that already exist will be skipped. If it is specified, the error is

ignored and the tables data will be inserted. The default value is N.

3. You have a rollback segment in a version 7.2 database that has expanded beyond

optimal, how can it be restored to optimal

Use the ALTER TABLESPACE ….. SHRINK command.

4. If the DEFAULT and TEMPORARY tablespace clauses are left out of a CREATE USER command what happens? Is this bad or good? Why

The user is assigned the SYSTEM tablespace as a default and temporary tablespace.

This is bad because it causes user objects and temporary segments to be placed into the

SYSTEM tablespace resulting in fragmentation and improper table placement (only

data dictionary objects and the system rollback segment should be in SYSTEM).

5. What are some of the Oracle provided packages that DBAs should be aware of

Oracle provides a number of packages in the form of the DBMS_ packages owned by

the SYS user. The packages used by DBAs may include: DBMS_SHARED_POOL,

DBMS_UTILITY, DBMS_SQL, DBMS_DDL, DBMS_SESSION, DBMS_OUTPUT

and DBMS_SNAPSHOT. They may also try to answer with the UTL*.SQL or

CAT*.SQL series of SQL procedures. These can be viewed as extra credit but aren?t

part of the answer.

6. What happens if the constraint name is left out of a constraint clause

The Oracle system will use the default name of SYS_Cxxxx where xxxx is a system

generated number. This is bad since it makes tracking which table the constraint

belongs to or what the constraint does harder.

7. What happens if a tablespace clause is left off of a primary key constraint clause

This results in the index that is automatically generated being placed in then users

default tablespace. Since this will usually be the same tablespace as the table is being

created in, this can cause serious performance problems.

8. What is the proper method for disabling and re-enabling a primary key constraint

You use the ALTER TABLE command for both. However, for the enable clause you

must specify the USING INDEX and TABLESPACE clause for primary keys.

9. What happens if a primary key constraint is disabled and then enabled without fully specifying the index clause

The index is created in the user?s default tablespace and all sizing information is lost.

Oracle doesn?t store this information as a part of the constraint definition, but only as

part of the index definition, when the constraint was disabled the index was dropped

and the information is gone.

10. (On UNIX) When should more than one DB writer process be used? How many should be used

If the UNIX system being used is capable of asynchronous IO then only one is required,

if the system is not capable of asynchronous IO then up to twice the number of disks

used by Oracle number of DB writers should be specified by use of the db_writers

initialization parameter.

11. You are using hot backup without being in archivelog mode, can you recover in the event of a failure? Why or why not

You can?t use hot backup without being in archivelog mode. So no, you couldn?t

recover.

12. What causes the “snapshot too old” error? How can this be prevented or mitigated

This is caused by large or long running transactions that have either wrapped onto their

own rollback space or have had another transaction write on part of their rollback space.

This can be prevented or mitigated by breaking the transaction into a set of smaller

transactions or increasing the size of the rollback segments and their extents.

13. How can you tell if a database object is invalid

By checking the status column of the DBA_, ALL_ or USER_OBJECTS views,

depending upon whether you own or only have permission on the view or are using a

DBA account.

13. A user is getting an ORA-00942 error yet you know you have granted them

permission on the table, what else should you check

You need to check that the user has specified the full name of the object (select empid

from scott.emp; instead of select empid from emp;) or has a synonym that balls to the

object (create synonym emp for scott.emp;)

14. A developer is trying to create a view and the database won?t let him. He has the

“DEVELOPER” role which has the “CREATE VIEW” system privilege and SELECT grants on the tables he is using, what is the problem

You need to verify the developer has direct grants on all tables used in the view. You

can?t create a stored object with grants given through views.

15. If you have an example table, what is the best way to get sizing data for the

production table implementation

The best way is to analyze the table and then use the data provided in the

DBA_TABLES view to get the average row length and other pertinent data for the

calculation. The quick and dirty way is to look at the number of blocks the table is

actually using and ratio the number of rows in the table to its number of blocks against

the number of expected rows.

16. How can you find out how many users are currently logged into the database? How

can you find their operating system id

There are several ways. One is to look at the v$session or v$process views. Another

way is to check the current_logins parameter in the v$sysstat view. Another if you are

on UNIX is to do a “ps -ef|grep oracle|wc -l? command, but this only works against a

single instance installation.

17. A user selects from a sequence and gets back two values, his select is:

SELECT pk_seq.nextval FROM dual;What is the problem

Somehow two values have been inserted into the dual table. This table is a single row,

single column table that should only have one value in it.

18. How can you determine if an index needs to be dropped and rebuilt

Run the ANALYZE INDEX command on the index to validate its structure and then

calculate the ratio of LF_BLK_LEN/LF_BLK_LEN+BR_BLK_LEN and if it isn?t near

1.0 (i.e. greater than 0.7 or so) then the index should be rebuilt. Or if the ratio

BR_BLK_LEN/ LF_BLK_LEN+BR_BLK_LEN is nearing 0.3

1. How can variables be passed to a SQL routine

By use of the & symbol. For passing in variables the numbers 1-8 can be used (&1,

&2,…,&8) to pass the values after the command into the SQLPLUS session. To be

prompted for a specific variable, place the ampersanded variable in the code itself:

“select * from dba_tables where owner=&owner_name;” . Use of double ampersands

tells SQLPLUS to resubstitute the value for each subsequent use of the variable, a

single ampersand will cause a reprompt for the value unless an ACCEPT statement is

used to get the value from the user.

2. You want to include a carriage return/linefeed in your output from a SQL script, how

can you do this

The best method is to use the CHR() function (CHR(10) is a return/linefeed) and the

concatenation function “||”. Another method, although it is hard to document and isn?t

always portable is to use the return/linefeed as a part of a quoted string.

3. How can you call a PL/SQL procedure from SQL

By use of the EXECUTE (short form EXEC) command.

4. How do you execute a host operating system command from within SQL

By use of the exclamation ball “!” (in UNIX and some other OS) or the HOST (HO)

command.

5. You want to use SQL to build SQL, what is this called and give an example

This is called dynamic SQL. An example would be:

set lines 90 pages 0 termout off feedback off verify off

spool drop_all.sql

select ?drop user ?||username||? cascade;? from dba_users

where username not in (“SYS?,?SYSTEM?);

spool off

Essentially you are looking to see that they know to include a command (in this case

DROP USER…CASCADE;) and that you need to concatenate using the ?||? the values

selected from the database.

6. What SQLPlus command is used to format output from a select

This is best done with the COLUMN command.

7. You want to group the following set of select returns, what can you group on

Max(sum_of_cost), min(sum_of_cost), count(item_no), item_no

The only column that can be grouped on is the “item_no” column, the rest have

aggregate functions associated with them.

8. What special Oracle feature allows you to specify how the cost based system treats

a SQL statement

The COST based system allows the use of HINTs to control the optimizer path

selection. If they can give some example hints such as FIRST ROWS, ALL ROWS,

USING INDEX, STAR, even better.

9. You want to determine the location of identical rows in a table before attempting to

place a unique index on the table, how can this be done

Oracle tables always have one guaranteed unique column, the rowid column. If you use

a min/max function against your rowid and then select against the proposed primary

key you can squeeze out the rowids of the duplicate rows pretty quick. For example:

select rowid from emp e

where e.rowid > (select min(x.rowid)

from emp x

where x.emp_no = e.emp_no);

In the situation where multiple columns make up the proposed key, they must all be

used in the where clause.

10. What is a Cartesian product

A Cartesian product is the result of an unrestricted join of two or more tables. The result

set of a three table Cartesian product will have x * y * z number of rows where x, y, z

correspond to the number of rows in each table involved in the join.

11. You are joining a local and a remote table, the network manager complains about

the traffic involved, how can you reduce the network traffic

Push the processing of the remote data to the remote instance by using a view to preselect

the information for the join. This will result in only the data required for the join

being sent across.

11. What is the default ordering of an ORDER BY clause in a SELECT statement

Ascending

12. What is tkprof and how is it used

The tkprof tool is a tuning tool used to determine cpu and execution times for SQL

statements. You use it by first setting timed_statistics to true in the initialization file and

then turning on tracing for either the entire database via the sql_trace parameter or for

the session using the ALTER SESSION command. Once the trace file is generated you

run the tkprof tool against the trace file and then look at the output from the tkprof tool.

This can also be used to generate explain plan output.

13. What is explain plan and how is it used

The EXPLAIN PLAN command is a tool to tune SQL statements. To use it you must

have an explain_table generated in the user you are running the explain plan for. This is

created using the utlxplan.sql script. Once the explain plan table exists you run the

explain plan command giving as its argument the SQL statement to be explained. The

explain_plan table is then queried to see the execution plan of the statement. Explain

plans can also be run using tkprof.

14. How do you set the number of lines on a page of output? The width

The SET command in SQLPLUS is used to control the number of lines generated per

page and the width of those lines, for example SET PAGESIZE 60 LINESIZE 80 will

generate reports that are 60 lines long with a line width of 80 characters. The

PAGESIZE and LINESIZE options can be shortened to PAGES and LINES.

15. How do you prevent output from coming to the screen

The SET option TERMOUT controls output to the screen. Setting TERMOUT OFF

turns off screen output. This option can be shortened to TERM.

16. How do you prevent Oracle from giving you informational messages during and after

a SQL statement execution

The SET options FEEDBACK and VERIFY can be set to OFF.

17. How do you generate file output from SQL

By use of the SPOOL command

1. A tablespace has a table with 30 extents in it. Is this bad? Why or why not.

Multiple extents in and of themselves aren?t bad. However if you also have chained

rows this can hurt performance.

2. How do you set up tablespaces during an Oracle installation?

You should always attempt to use the Oracle Flexible Architecture standard or another

partitioning scheme to ensure proper separation of SYSTEM, ROLLBACK, REDO

LOG, DATA, TEMPORARY and INDEX segments.

3. You see multiple fragments in the SYSTEM tablespace, what should you check first?

Ensure that users don?t have the SYSTEM tablespace as their TEMPORARY or

DEFAULT tablespace assignment by checking the DBA_USERS view.

4. What are some indications that you need to increase the SHARED_POOL_SIZE

parameter?

Poor data dictionary or library cache hit ratios, getting error ORA-04031. Another

indication is steadily decreasing performance with all other tuning parameters the same.

5. What is the general guideline for sizing db_block_size and db_multi_block_read for an

application that does many full table scans?

Oracle almost always reads in 64k chunks. The two should have a product equal to 64

or a multiple of 64.

6. What is the fastest query method for a table

Fetch by rowed

7. Explain the use of TKPROF? What initialization parameter should be turned on to get

full TKPROF output?

The tkprof tool is a tuning tool used to determine cpu and execution times for SQL

statements. You use it by first setting timed_statistics to true in the initialization file and

then turning on tracing for either the entire database via the sql_trace parameter or for

the session using the ALTER SESSION command. Once the trace file is generated you

run the tkprof tool against the trace file and then look at the output from the tkprof tool.

This can also be used to generate explain plan output.

8. When looking at v$sysstat you see that sorts (disk) is high. Is this bad or good? If

bad -How do you correct it?

If you get excessive disk sorts this is bad. This indicates you need to tune the sort area

parameters in the initialization files. The major sort are parameter is the

SORT_AREA_SIZe parameter.

9. When should you increase copy latches? What parameters control copy latches

When you get excessive contention for the copy latches as shown by the “redo copy”

latch hit ratio. You can increase copy latches via the initialization parameter

LOG_SIMULTANEOUS_COPIES to twice the number of CPUs on your system.

10. Where can you get a list of all initialization parameters for your instance? How about

an indication if they are default settings or have been changed

You can look in the init.ora file for an indication of manually set parameters. For all

parameters, their value and whether or not the current value is the default value, look in

the v$parameter view.

11. Describe hit ratio as it pertains to the database buffers. What is the difference

between instantaneous and cumulative hit ratio and which should be used for tuning

The hit ratio is a measure of how many times the database was able to read a value from

the buffers verses how many times it had to re-read a data value from the disks. A value

greater than 80-90% is good, less could indicate problems. If you simply take the ratio

of existing parameters this will be a cumulative value since the database started. If you

do a comparison between pairs of readings based on some arbitrary time span, this is

the instantaneous ratio for that time span. Generally speaking an instantaneous reading

gives more valuable data since it will tell you what your instance is doing for the time it

was generated over.

12. Discuss row chaining, how does it happen? How can you reduce it? How do you

correct it

Row chaining occurs when a VARCHAR2 value is updated and the length of the new

value is longer than the old value and won?t fit in the remaining block space. This

results in the row chaining to another block. It can be reduced by setting the storage

parameters on the table to appropriate values. It can be corrected by export and import

of the effected table.

13. When looking at the estat events report you see that you are getting busy buffer

waits. Is this bad? How can you find what is causing it

Buffer busy waits could indicate contention in redo, rollback or data blocks. You need

to check the v$waitstat view to see what areas are causing the problem. The value of the

“count” column tells where the problem is, the “class” column tells you with what.

UNDO is rollback segments, DATA is data base buffers.

14. If you see contention for library caches how can you fix it

Increase the size of the shared pool.

15. If you see statistics that deal with “undo” what are they really talking about

Rollback segments and associated structures.

16. If a tablespace has a default pctincrease of zero what will this cause (in relationship

to the smon process)

The SMON process won?t automatically coalesce its free space fragments.

17. If a tablespace shows excessive fragmentation what are some methods to

defragment the tablespace? (7.1,7.2 and 7.3 only)

In Oracle 7.0 to 7.2 The use of the ‘alter session set events ‘immediate trace name

coalesce level ts#’;? command is the easiest way to defragment contiguous free space

fragmentation. The ts# parameter corresponds to the ts# value found in the ts$ SYS

table. In version 7.3 the ?alter tablespace coalesce;? is best. If the free space isn?t

contiguous then export, drop and import of the tablespace contents may be the only way

to reclaim non-contiguous free space.

18. How can you tell if a tablespace has excessive fragmentation

If a select against the dba_free_space table shows that the count of a tablespaces extents

is greater than the count of its data files, then it is fragmented.

19. You see the following on a status report:

redo log space requests 23

redo log space wait time 0

Is this something to worry about? What if redo log space wait time is high? How

can you fix this

Since the wait time is zero, no. If the wait time was high it might indicate a need for

more or larger redo logs.

20. What can cause a high value for recursive calls? How can this be fixed

A high value for recursive calls is cause by improper cursor usage, excessive dynamic

space management actions, and or excessive statement re-parses. You need to determine

the cause and correct it By either relinking applications to hold cursors, use proper

space management techniques (proper storage and sizing) or ensure repeat queries are

placed in packages for proper reuse.

21. If you see a pin hit ratio of less than 0.8 in the estat library cache report is this a

problem? If so, how do you fix it

This indicate that the shared pool may be too small. Increase the shared pool size.

22. If you see the value for reloads is high in the estat library cache report is this a

matter for concern

Yes, you should strive for zero reloads if possible. If you see excessive reloads then

increase the size of the shared pool.

23. You look at the dba_rollback_segs view and see that there is a large number of

shrinks and they are of relatively small size, is this a problem? How can it be fixed if it is

a problem

A large number of small shrinks indicates a need to increase the size of the rollback

segment extents. Ideally you should have no shrinks or a small number of large shrinks.

To fix this just increase the size of the extents and adjust optimal accordingly.

24. You look at the dba_rollback_segs view and see that you have a large number of

wraps is this a problem

A large number of wraps indicates that your extent size for your rollback segments are

probably too small. Increase the size of your extents to reduce the number of wraps.

You can look at the average transaction size in the same view to get the information on

transaction size.

25. In a system with an average of 40 concurrent users you get the following from a

query on rollback extents:

ROLLBACK CUR EXTENTS

——————— ————————–

R01 11

R02 8

R03 12

R04 9

SYSTEM 4

26. You have room for each to grow by 20 more extents each. Is there a problem? Should

you take any action

No there is not a problem. You have 40 extents showing and an average of 40

concurrent users. Since there is plenty of room to grow no action is needed.

27. You see multiple extents in the temporary tablespace. Is this a problem

As long as they are all the same size this isn?t a problem. In fact, it can even improve

performance since Oracle won?t have to create a new extent when a user needs one.

28. Define OFA.

OFA stands for Optimal Flexible Architecture. It is a method of placing directories and

files in an Oracle system so that you get the maximum flexibility for future tuning and

file placement.

29. How do you set up your tablespace on installation

The answer here should show an understanding of separation of redo and rollback, data

and indexes and isolation os SYSTEM tables from other tables. An example would be

to specify that at least 7 disks should be used for an Oracle installation so that you can

place SYSTEM tablespace on one, redo logs on two (mirrored redo logs) the

TEMPORARY tablespace on another, ROLLBACK tablespace on another and still

have two for DATA and INDEXES. They should indicate how they will handle archive

logs and exports as well. As long as they have a logical plan for combining or further

separation more or less disks can be specified.

30. What should be done prior to installing Oracle (for the OS and the disks)

adjust kernel parameters or OS tuning parameters in accordance with installation guide.

Be sure enough contiguous disk space is available.

31. You have installed Oracle and you are now setting up the actual instance. You have

been waiting an hour for the initialization script to finish, what should you check first to

determine if there is a problem

Check to make sure that the archiver isn?t stuck. If archive logging is turned on during

install a large number of logs will be created. This can fill up your archive log

destination causing Oracle to stop to wait for more space.

32. When configuring SQLNET on the server what files must be set up

INITIALIZATION file, TNSNAMES.ORA file, SQLNET.ORA file

33. When configuring SQLNET on the client what files need to be set up

SQLNET.ORA, TNSNAMES.ORA

34. What must be installed with ODBC on the client in order for it to work with Oracle

SQLNET and PROTOCOL (for example: TCPIP adapter) layers of the transport

programs.

35. You have just started a new instance with a large SGA on a busy existing server.

Performance is terrible, what should you check for

The first thing to check with a large SGA is that it isn?t being swapped out.

36. What OS user should be used for the first part of an Oracle installation (on UNIX)

You must use root first.

37. When should the default values for Oracle initialization parameters be used as is

Never

38. How many control files should you have? Where should they be located

At least 2 on separate disk spindles. Be sure they say on separate disks, not just file

systems.

39. How many redo logs should you have and how should they be configured for

maximum recoverability

You should have at least three groups of two redo logs with the two logs each on a

separate disk spindle (mirrored by Oracle). The redo logs should not be on raw devices

on UNIX if it can be avoided.

40. You have a simple application with no “hot” tables (i.e. uniform IO and access

requirements). How many disks should you have assuming standard layout for SYSTEM,

USER, TEMP and ROLLBACK tablespaces

At least 7, see disk configuration answer above.

41. Describe third normal form

Something like: In third normal form all attributes in an entity are related to the primary

key and only to the primary key

42. Is the following statement true or false:

“All relational databases must be in third normal form”

False. While 3NF is good for logical design most databases, if they have more than just

a few tables, will not perform well using full 3NF. Usually some entities will be

denormalized in the logical to physical transfer process.

43. What is an ERD

An ERD is an Entity-Relationship-Diagram. It is used to show the entities and

relationships for a database logical model.

44. Why are recursive relationships bad? How do you resolve them

A recursive relationship (one where a table relates to itself) is bad when it is a hard

relationship (i.e. neither side is a “may” both are “must”) as this can result in it not

being possible to put in a top or perhaps a bottom of the table (for example in the

EMPLOYEE table you couldn?t put in the PRESIDENT of the company because he has

no boss, or the junior janitor because he has no subordinates). These type of

relationships are usually resolved by adding a small intersection entity.

45. What does a hard one-to-one relationship mean (one where the relationship on both

ends is “must”)

Expected answer: This means the two entities should probably be made into one entity.

46. How should a many-to-many relationship be handled

By adding an intersection entity table

47. What is an artificial (derived) primary key? When should an artificial (or derived)

primary key be used

A derived key comes from a sequence. Usually it is used when a concatenated key

becomes too cumbersome to use as a foreign key.

48. When should you consider denormalization

Whenever performance analysis indicates it would be beneficial to do so without

compromising data integrity.

49. How can you determine if an Oracle instance is up from the operating system level

There are several base Oracle processes that will be running on multi-user operating

systems, these will be smon, pmon, dbwr and lgwr. Any answer that has them using

their operating system process showing feature to check for these is acceptable. For

example, on UNIX a ps -ef|grep dbwr will show what instances are up.

50. Users from the PC clients are getting messages indicating :

ORA-06114: (Cnct err, can’t get err txt. See Servr Msgs & Codes Manual)

What could the problem be

The instance name is probably incorrect in their connection string.

51. Users from the PC clients are getting the following error stack:

ERROR: ORA-01034: ORACLE not available

ORA-07318: smsget: open error when opening sgadef.dbf file.

HP-UX Error: 2: No such file or directory

What is the probable cause

The Oracle instance is shutdown that they are trying to access, restart the instance.

52. How can you determine if the SQLNET process is running for SQLNET V1? How about

V2

For SQLNET V1 check for the existence of the orasrv process. You can use the

command “tcpctl status” to get a full status of the V1 TCPIP server, other protocols

have similar command formats. For SQLNET V2 check for the presence of the

LISTENER process(s) or you can issue the command “lsnrctl status”.

53. What file will give you Oracle instance status information? Where is it located

The alert.ora log. It is located in the directory specified by the background_dump_dest

parameter in the v$parameter table.

54. Users aren?t being allowed on the system. The following message is received:

ORA-00257 archiver is stuck. Connect internal only, until freed

What is the problem

The archive destination is probably full, backup the archive logs and remove them and

the archiver will re-start.

55. Where would you look to find out if a redo log was corrupted assuming you are using

Oracle mirrored redo logs

There is no message that comes to the SQLDBA or SRVMGR programs during startup

in this situation, you must check the alert.log file for this information.

56. You attempt to add a datafile and get:

ORA-01118: cannot add anymore datafiles: limit of 40 exceeded

What is the problem and how can you fix it

When the database was created the db_files parameter in the initialization file was set to

40. You can shutdown and reset this to a higher value, up to the value of

MAX_DATAFILES as specified at database creation. If the MAX_DATAFILES is set

to low, you will have to rebuild the control file to increase it before proceeding.

57. You look at your fragmentation report and see that smon hasn?t coalesced any of

you tablespaces, even though you know several have large chunks of contiguous free

extents. What is the problem

Check the dba_tablespaces view for the value of pct_increase for the tablespaces. If

pct_increase is zero, smon will not coalesce their free space.

58. Your users get the following error:

ORA-00055 maximum number of DML locks exceeded

What is the problem and how do you fix it

The number of DML Locks is set by the initialization parameter DML_LOCKS. If this

value is set to low (which it is by default) you will get this error. Increase the value of

DML_LOCKS. If you are sure that this is just a temporary problem, you can have them

wait and then try again later and the error should clear.

59. You get a call from you backup DBA while you are on vacation. He has corrupted all

of the control files while playing with the ALTER DATABASE BACKUP CONTROLFILE

command. What do you do

As long as all datafiles are safe and he was successful with the BACKUP controlfile

command you can do the following:

CONNECT INTERNAL

STARTUP MOUNT

(Take any read-only tablespaces offline before next step ALTER DATABASE

DATAFILE …. OFFLINE;)

RECOVER DATABASE USING BACKUP CONTROLFILE

ALTER DATABASE OPEN RESETLOGS;

(bring read-only tablespaces back online)

Shutdown and backup the system, then restart

If they have a recent output file from the ALTER DATABASE BACKUP CONTROL

FILE TO TRACE; command, they can use that to recover as well.

If no backup of the control file is available then the following will be required:

CONNECT INTERNAL

STARTUP NOMOUNT

CREATE CONTROL FILE …..;

However, they will need to know all of the datafiles, logfiles, and settings for

MAXLOGFILES, MAXLOGMEMBERS, MAXLOGHISTORY, MAXDATAFILES

for the database to use the command.

Oracle DBA Interview questions

Differentiate between TRUNCATE and DELETE.

The Delete command will log the data changes in the log file where as the truncate will

simply remove the data without it. Hence Data removed by Delete command can be

rolled back but not the data removed by TRUNCATE. Truncate is a DDL statement

whereas DELETE is a DML statement.

What is the maximum buffer size that can be specified using the

DBMS_OUTPUT.ENABLE function?

1000000

Can you use a commit statement within a database trigger?

Yes, if you are using autonomous transactions in the Database triggers.

What is an UTL_FILE? What are different procedures and functions associated

with it?

The UTL_FILE package lets your PL/SQL programs read and write operating system

(OS) text files. It provides a restricted version of standard OS stream file input/output

(I/O).

Subprogram -Description

FOPEN function-Opens a file for input or output with the default line size.

IS_OPEN function -Determines if a file handle refers to an open file.

FCLOSE procedure -Closes a file.

FCLOSE_ALL procedure -Closes all open file handles.

GET_LINE procedure -Reads a line of text from an open file.

PUT procedure-Writes a line to a file. This does not append a line terminator.

NEW_LINE procedure-Writes one or more OS-specific line terminators to a file.

PUT_LINE procedure -Writes a line to a file. This appends an OS-specific line

terminator.

PUTF procedure -A PUT procedure with formatting.

FFLUSH procedure-Physically writes all pending output to a file.

FOPEN function -Opens a file with the maximum line size specified.

Difference between database triggers and form triggers?

Database triggers are fired whenever any database action like INSERT, UPATE,

DELETE, LOGON LOGOFF etc occurs. Form triggers on the other hand are fired in

response to any event that takes place while working with the forms, say like navigating

from one field to another or one block to another and so on.

What is OCI. What are its uses?

OCI is Oracle Call Interface. When applications developers demand the most powerful

interface to the Oracle Database Server, they call upon the Oracle Call Interface (OCI).

OCI provides the most comprehensive access to all of the Oracle Database functionality.

The newest performance, scalability, and security features appear first in the OCI API. If

you write applications for the Oracle Database, you likely already depend on OCI. Some

types of applications that depend upon OCI are:

· PL/SQL applications executing SQL

· C++ applications using OCCI

· Java applications using the OCI-based JDBC driver

· C applications using the ODBC driver

· VB applications using the OLEDB driver

· Pro*C applications

· Distributed SQL

What are ORACLE PRECOMPILERS?

A precompiler is a tool that allows programmers to embed SQL statements in high-level

source programs like C, C++, COBOL, etc. The precompiler accepts the source program

as input, translates the embedded SQL statements into standard Oracle runtime library

calls, and generates a modified source program that one can compile, link, and execute in

the usual way. Examples are the Pro*C Precompiler for C, Pro*Cobol for Cobol, SQLJ

for Java etc.

What is syntax for dropping a procedure and a function? Are these operations

possible?

Drop Procedure/Function ; yes, if they are standalone procedures or functions. If they are

a part of a package then one have to remove it from the package definition and body and

recompile the package.

How to check if Apps 11i System is Autoconfig enabled ?

Under $AD_TOP/bin check for file adcfginfo.sh and if this exists use adcfginfo.sh

contextfile=<CONTEXT> show=enabled

If this file is not there , look for any configuration file under APPL_TOP if system is

Autoconfig enabled then you will see entry like

How to check if Oracle Apps 11i System is Rapid Clone enabled ?

For syetem to be Rapid Clone enabled , it should be Autoconfig enabled (Check above

How to confirm if Apps 11i is Autoconfig enabled). You should have Rapid Clone

Patches applied , Rapid Clone is part of Rapid Install Product whose Family Pack Name

is ADX. By default all Apps 11i Instances 11.5.9 and above are Autoconfig and Rapid

Clone enabled.

Whats is difference between two env files in <CONTEXT>.env and

APPS<CONTEXT>.env under $APPL_TOP ?

APPS<CONTEXT>.env is main environment file which inturn calls other environment

files like <CONTEXT>.env under $APPL_TOP, <CONTEXT>.env under 806

ORACLE_HOME and custom.env for any Customized environment files.

Whats main concurrent Manager types.

# ICM – Internal Concurrent Manager which manages concurrent Managers

# Standard Managers – Which Manage processesing of requests.

# CRM – Conflict Resolution Managers , resolve conflicts in case of incompatibility.

Whats US directory in $AD_TOP or under various product TOP’s .

US directory is defauly language directory in Oracle Applications. If you have multiple

languages Installed in your Applications then you will see other languages directories

besides US, that directory will contain reports, fmx and other code in that respective

directory like FR for France, AR for arabic, simplifies chinese or spanish.

Where is Concurrent Manager log file location.

By default standard location is $APPLCSF/$APPLLOG , in some cases it can go to

$FND_TOP/log as well.

Where would i find .rf9 file, and what execatly it dose ?

These files are used during restart of patch in case of patch failure because of some

reason.

Where is appsweb.cfg or appsweb_$CONTEXT.cfg stored and why its used ?

This file is defined by environment variable FORMS60_WEB_CONFIG_FILE This is

usually in directory $OA_HTML/bin on forms tier.

This file is used by any forms client session. When a user try to access forms , f60webmx

picks up this file and based on this configuration file creates a forms session to

user/client.

What is Multi Node System ?

Multi Node System in Oracle Applications 11i means you have Applications 11i

Component on more than one system. Typical example is Database, Concurrent Manager

on one machine and forms, Web Server on second machine is example of Two Node

System.

Can a function take OUT parameters. If not why?

yes, IN, OUT or IN OUT.

Can the default values be assigned to actual parameters?

Yes. In such case you don’t need to specify any value and the actual parameter will take

the default value provided in the function definition.

What is difference between a formal and an actual parameter?

The formal parameters are the names that are declared in the parameter list of the header

of a module. The actual parameters are the values or expressions placed in the parameter

list of the actual call to the module.

What are different modes of parameters used in functions and procedures?

There are three different modes of parameters: IN, OUT, and IN OUT.

IN – The IN parameter allows you to pass values in to the module, but will not pass

anything out of the module and back to the calling PL/SQL block. In other words, for the

purposes of the program, its IN parameters function like constants. Just like constants, the

value of the formal IN parameter cannot be changed within the program. You cannot

assign values to the IN parameter or in any other way modify its value.

IN is the default mode for parameters. IN parameters can be given default values in the

program header.

OUT – An OUT parameter is the opposite of the IN parameter. Use the OUT parameter to

pass a value back from the program to the calling PL/SQL block. An OUT parameter is

like the return value for a function, but it appears in the parameter list and you can, of

course, have as many OUT parameters as you like.

Inside the program, an OUT parameter acts like a variable that has not been initialised. In

fact, the OUT parameter has no value at all until the program terminates successfully

(without raising an exception, that is). During the execution of the program, any

assignments to an OUT parameter are actually made to an internal copy of the OUT

parameter. When the program terminates successfully and returns control to the calling

block, the value in that local copy is then transferred to the actual OUT parameter. That

value is then available in the calling PL/SQL block.

IN OUT – With an IN OUT parameter, you can pass values into the program and return a

value back to the calling program (either the original, unchanged value or a new value set

within the program). The IN OUT parameter shares two restrictions with the OUT

parameter:

An IN OUT parameter cannot have a default value.

An IN OUT actual parameter or argument must be a variable. It cannot be a constant,

literal, or expression, since these formats do not provide a receptacle in which PL/SQL

can place the outgoing value.

Difference between procedure and function.

A function always returns a value, while a procedure does not. When you call a function

you must always assign its value to a variable.

Can cursor variables be stored in PL/SQL tables. If yes how. If not why?

Yes. Create a cursor type – REF CURSOR and declare a cursor variable of that type.

DECLARE

/* Create the cursor type. */

TYPE company_curtype IS REF CURSOR RETURN company%ROWTYPE;

/* Declare a cursor variable of that type. */

company_curvar company_curtype;

/* Declare a record with same structure as cursor variable. */

company_rec company%ROWTYPE;

BEGIN

/* Open the cursor variable, associating with it a SQL statement. */

OPEN company_curvar FOR SELECT * FROM company;

/* Fetch from the cursor variable. */

FETCH company_curvar INTO company_rec;

/* Close the cursor object associated with variable. */

CLOSE company_curvar;

END;

Can you clone from multi node system to single node system and vice versa ?

Yes , this is now supported via Rapid Clone, Check if your system has all prereq. patches

for Rapid Clone and you are on latest rapid clone patch.

Does rapid clone takes care of Updating Global oraInventory or you have to register

manually in Global OraInventory after clone ?

Rapid Clone will automatically Update Global oraInventory during configuration phase.

You don’t have to do any thing manually for Global oraInventory.

What is .dbc file , where its stored , whats use of .dbc file ?

dbc as name says is database connect descriptor file which stores database connection

information used by application tier to connect to database. This file is in directory

$FND_TOP/secure also called as FND_SECURE

Whats things you do to reduce patch timing ?

You can take advantage of following –

# Merging patches via admrgpch

# Use various adpatch options like nocompiledb or nocompilejsp

# Use defaults file

# Staged APPL_TOP during upgrades

# Increase batch size (Might result into negative )

How you put Applications 11i in Maintenance mode ?

Use adadmin to change Maintenance mode is Oracle Apps. With AD.I you need to enable

maintenance mode in order to apply apps patch via adpatch utility. If you don’t want to

put apps in maintenance mode you can use adpatch options=hotpatch feature.

Can you apply patch without putting Applications 11i in Maintenance mode ?

Yes, use options=hotpatch as mentioned above with adpatch.

What are various options available with adpatch ?

Various options available with adpatch depending on your AD version are autoconfig,

check_exclusive, checkfile, compiledb, compilejsp, copyportion, databaseprtion,

generateportion, hotpatch, integrity, maintainmrc, parallel, prereq, validate

ADIDENT UTILITY is used for what ?

ADIDENT UTILITY in oracle apps is used to find version of any file . AD Identification.

for ex. “adident Header <filename>

How do you pass cursor variables in PL/SQL?

Pass a cursor variable as an argument to a procedure or function. You can, in essence,

share the results of a cursor by passing the reference to that result set.

How do you open and close a cursor variable. Why it is required?

Using OPEN cursor_name and CLOSE cursor_name commands. The cursor must be

opened before using it in order to fetch the result set of the query it is associated with.

The cursor needs to be closed so as to release resources earlier than end of transaction, or

to free up the cursor variable to be opened again.

What should be the return type for a cursor variable. Can we use a scalar data type

as return type?

The return type of a cursor variable can be %ROWTYPE or record_name%TYPE or a

record type or a ref cursor type. A scalar data type like number or varchar can’t be used

but a record type may evaluate to a scalar value.

What is use of a cursor variable? How it is defined?

Cursor variable is used to mark a work area where Oracle stores a multi-row query output

for processing. It is like a pointer in C or Pascal. Because it is a TYPE, it is defined as

TYPE REF CURSOR RETURN ;

What WHERE CURRENT OF clause does in a cursor?

The Where Current Of statement allows you to update or delete the record that was last

fetched by the cursor.

Difference between NO DATA FOUND and %NOTFOUND

NO DATA FOUND is an exception which is raised when either an implicit query returns

no data, or you attempt to reference a row in the PL/SQL table which is not yet defined.

SQL%NOTFOUND, is a BOOLEAN attribute indicating whether the recent SQL

statement does not match to any row.

What is a cursor for loop?

A cursor FOR loop is a loop that is associated with (actually defined by) an explicit

cursor or a SELECT statement incorporated directly within the loop boundary. Use the

cursor FOR loop whenever (and only if) you need to fetch and process each and every

record from a cursor, which is a high percentage of the time with cursors.

What is iAS Patch ?

iAS Patch are patches released to fix bugs associated with IAS_ORACLE_HOME (Web

Server Component) Usually these are shiiped as Shell scripts and you apply iAS patches

by executing Shell script. Note that by default ORACLE_HOME is pointing to 8.0.6

ORACLE_HOME and if you are applying iAS patch export ORACLE_HOME to iAS .

You can do same by executing environment file under $IAS_ORACLE_HOME

If we run autoconfig which files will get effected ?

In order to check list of files changes during Autoconfig , you can run adchkcfg utility

which will generate HTML report. This report will list all files and profile options going

to change when you run AutoConfig.

What is difference between .xml file and AutoConfig ?

Autoconfig is Utility to configure your Oracle Application environment. .xml file is

repository of all configuration from which AutoConfig picks configuration and polulates

related files

.

What is .lgi files ?

lgi files are created with patching along with .log files . .lgi files are informative log files

containing information related to patch. You can check .lgi files to see what activities

patch has done. Usually informative logs.

How will you skip worker during patch ?

If in your adctrl there are six option shown then seventh is hidden option.(If there are

seven options visible then 8th option is to Skip worker depending on ad version).

Which two tables created at start of Apps Patch and drops at end of Patch ?

FND_INSTALLED_PROCESS and AD_DEFFERED_JOBS are the tables that get

updated while applying a patch mainly d or unified driver.

How to compile an Oracle Reports file ?

Utility adrepgen is used to compile Reports. Synatx is given below adrepgen

userid=apps<psswd> source = $PRODUCT_TOPsrwfilename.rdf

dest=$PRODUCT_TOPsrwfilename.rdf stype=rdffile dtype=rdffile logfile=x.log

overwrite=yes batch=yes dunit=character

What is difference between AD_BUGS and AD_APPLID_PATCHES ?

AD_BUGS holds information about the various Oracle Applications bugs whose fixes

have been applied (ie. patched) in the Oracle Applications installation.

AD_APPLIED_PATCHES holds information about the “distinct” Oracle Applications

patches that have been applied. If 2 patches happen to have the same name but are

different in content (eg. “merged” patches), then they are considered distinct and this

table will therefore hold 2 records.

What is ADSPLICE UTILITY ?

ADSPLICE UTILITY in oracle apps is utility to add a new product.

How can you licence a product after installation ?

You can use ad utility adlicmgr to licence product in Oracle Apps.

What is MRC ? What you do as Apps DBA for MRC ?

MRC also called as Multiple Reporting Currency in oracle Apps. Default you have

currency in US Dollars but if your organization operating books are in other currency

then you as apps dba need to enable MRC in Apps. How to enable MRC coming soon..

What is access_log in apache , what entries are recored in access_log ? Where is

default location of thsi file ?

access_log in Oracle Application Server records all users accessing oracle applications

11i. This file location is defined in httpd.conf with default location at

$IAS_ORACLE_HOME/Apache/Apache/logs. Entries in this file is defined by directive

LogFormat in httpd.conf Typical entry in access_log is

198.0.0.1 – – [10/Sep/2006:18:37:17 +0100] “POST /OA_HTML/OA.jsp?…. HTTP/1.1″

200 28035

where 200 is HTTP status code and last digits 28035 is bytes dowloaded as this page(Size

of page)

Where is Jserv configuration files stored ?

Jserv configuration files are stored in $IAS_ORACLE_HOME/Apache/Jserv/etc

Where is applications start/stop scripts stored ?

applications start/stop scripts are in directory

$COMMON_TOP/admin/scripts/$CONTEXT_NAME

What are main configuration files in Web Server (Apache) ?

Main configuration files in Oracle Apps Web Server are

# httpd.conf, apps.conf, oracle_apache.conf, httpd_pls.conf

# jserv.conf, ssp_init.txt, jserv.properties, zone.properties

# plsql.conf, wdbsvr.app, plsql.conf

Can C driver in apps patch create Invalid Object in database ?

No , C driver only copies files in File System. Database Object might be invalidated

during D driver when these objects are created/dropped/modified.

What is dev60cgi and f60cgi ?

CGI stands for Common Gateway Interface and these are Script Alias in Oracle Apps

used to access forms server . Usually Form Server access directly via

http://hostname:port/dev60cgi/f60cgi

Why does a worker fails in Oracle Apps Patch and few scenarios in which it failed

for you ?

Apps Patch worker can fail in case it doesn’t find expected data, object, files or any thing

which driver is trying to update/edit/modify. Possible symptoms may be underlying

tables/objects are invalid, a prereq patch is missing , login information is incorrect,

inconsistency in seeded data…

What is difference between mod_osso and mod_ose in Oracle HTTP Server ?

mod_osso is Oracle Single Sign-On Module where as mod_ose is module for Oracle

Servlet Engine.

mod_osso is module in Oracle’s HTTP Server serves as Conduit between Oracle Apache

Server and Singl Sign-On Server where as mod_ose is also another module in Oracle’s

HTTP Server serves as conduit between Oracle Apache and Oracle Servlet Engine.

What is difference between COMPILE_ALL=SPECIAL and COMPILE=ALL while

compiling Forms ?

Both the options will compile all the PL/SQL in the resultant .FMX, .PLX, or .MMX file

but COMPILE_ALL=YES also changes the cached version in the source .FMB, .PLL, or

.MMB file. This confuses version control and build tools (CVS, Subversion, make,

scons); they believe you’ve made significant changes to the source.

COMPILE_ALL=SPECIAL does not do this.

What is GSM in Oracle application E-Business Suite ?

GSM stands for Generic Service Management Framework. Oracle E-Business Suite

consist of various compoennts like Forms, Reports, Web Server, Workflow, Concurrent

Manager ..

Earlier each service used to start at their own but managing these services (given that)

they can be on various machines distributed across network. So Generic Service

Management is extension of Concurrent Processing which manages all your services ,

provide fault tolerance (If some service is down ICM through FNDSM and other

processes will try to start it even on remote server) With GSM all services are centrally

managed via this Framework.

What is FNDSM ?

FNDSM is executable and core component in GSM ( Generic Service Management

Framework discussed above). You start FNDSM services via APPS listener on all Nodes

in Application Tier in E-Business Suite.

What are cursor attributes?

Cursor attributes are used to get the information about the current status of your cursor.

Both explicit and implicit cursors have four attributes, as shown:

Name Description

%FOUND Returns TRUE if record was fetched successfully, FALSE otherwise.

%NOTFOUND Returns TRUE if record was not fetched successfully, FALSE otherwise.

%ROWCOUNT Returns number of records fetched from cursor at that point in time.

%ISOPEN Returns TRUE if cursor is open, FALSE otherwise.

Difference between an implicit and an explicit cursor.

The implicit cursor is used by Oracle server to test and parse the SQL statements and the

explicit cursors are declared by the programmers.

What is a cursor?

A cursor is a mechanism by which you can assign a name to a “select statement” and

manipulate the information within that SQL statement.

What is the purpose of a cluster?

A cluster provides an optional method of storing table data. A cluster is comprised of a

group of tables that share the same data blocks, which are grouped together because they

share common columns and are often used together. For example, the EMP and DEPT

table share the DEPTNO column. When you cluster the EMP and DEPT, Oracle

physically stores all rows for each department from both the EMP and DEPT tables in the

same data blocks. You should not use clusters for tables that are frequently accessed

individually.

How do you find the number of rows in a Table ?

select count(*) from table, or from NUM_ROWS column of user_tables if the table

statistics has been collected.

Display the number value in Words?

What is a pseudo column. Give some examples?

Information such as row numbers and row descriptions are automatically stored by

Oracle and is directly accessible, ie. not through tables. This information is contained

within pseudo columns. These pseudo columns can be retrieved in queries. These pseudo

columns can be included in queries which select data from tables.

Available Pseudo Columns

· ROWNUM – row number. Order number in which a row value is retrieved.

· ROWID – physical row (memory or disk address) location, ie. unique row identification.

· SYSDATE – system or today’s date.

· UID – user identification number indicating the current user.

· USER – name of currently logged in user.

Whats is location of access_log file ?

access_log file by default is located in $IAS_ORACLE_HOME/ Apache/Apache/logs.

Location of this file is defined in httpd.conf by patameter CustomLog or TransferLog

What is your Oracle Apps 11i Webserver Version and how to find it ?

From 11.5.8 to 11.5.10 Webserver version is iAS 1.0.2.2.2, In order to find version under

$IAS_ORACLE_HOME/Apache/Apache/bin execute ./httpd -version

./httpd -version

Server version: Oracle HTTP Server Powered by Apache/1.3.19

Server built: Dec 6 2005 14:59:13 (iAS 1.0.2.2.2 rollup 5)

What is Location of Jserv configuration files ?

Jserv configuration files are located in $IAS_ORACLE_HOME /Apache/Jserv/etc .

What is plssql/database cache ?

In order to improve performance mod_pls (Apache component) caches some database

content to file. This database/plssql cache is usually of type session and plsql cache

# session cache is used to store session information.

# plsql cache is used to store plsql cache i.e. used by mod_pls

Where is DATABASE/PLSSQL cache stored ?

PLSSQL and session cache are stored under $IAS_ORACLE_HOME/

Apache/modplsql/cache directory.

What is *.DBC file and whats is location of DBC file ?

DBC as name stands for is database connect descriptor file used to connect to database.

This file by default located in $FND_TOP/secure directory also called as

$FND_SECURE directory.

What is content of DBC file and why its important ?

DBC file is quite important as whenever Java or any other program like forms want to

connect to database it uses DBC file. Typical entry in DBC file is

GUEST_USER_PWD

APPS_JDBC_URL

DB_HOST

What are few profile options which you update after cloning ?

Rapid clone updates profile options specific to site level . If you have any profile option

set at other levels like server, responsibility, user….level then reset them.

How to retrieve SYSADMIN password ?

If forgot password link is enabled and SYSADMIN account is configured with mail id

user forget password link else you can reset sSYSADMIN password via FNDCPASS.

Whats is TWO_TASK in Oracle Database ?

TWO_TASK mocks your tns alias which you are going to use to connect to database.

Lets assume you have database client with tns alias defined as PROD to connect to

Database PROD on machine teachmeoracle.com listening on port 1521. Then usual way

to connect is sqlplus username/passwd@PROD ; now if you don’t want to use @PROD

then you set TWO_TASK=PROD and then can simply use sqlplus username/passwd then

sql will check that it has to connect to tnsalias define by value PROD i.e. TWO_TASK

What is GWYUID ?

GWYUID , stands for Gateway User ID and password. Usually like APPLSYSPUB/PUB

Where GWYUID defined and what is its used in Oracle Applications ?

GWYUID is defined in dbc i.e. Database Connect Descriptor file . It is used to connect to

database by think clients.

If APPS_MRC schema is not used in 11.5.10 and higher then How MRC is

working ?

For products like Payable, Recievables which uses MRC and if MRC is enabled then

each transaction table in base schema related to currency now has an assoicated MRC

Subtables.

When you apply C driver patch does it require database to be Up and Why ?

Yes , database and db listener should be Up when you apply any driver patch in apps.

even if driver is not updating any database object connection is required to validate

appsand other schema and to upload patch history information in database tables.

How you will avoid your query from using indexes?

By changing the order of the columns that are used in the index, in the Where condition,

or by concatenating the columns with some constant values.

What is a OUTER JOIN?

An OUTER JOIN returns all rows that satisfy the join condition and also returns some or

all of those rows from one table for which no rows from the other satisfy the join

condition.

Which is more faster – IN or EXISTS?

Well, the two are processed very differently.

Select * from T1 where x in ( select y from T2 )

is typically processed as:

select *

from t1, ( select distinct y from t2 ) t2

where t1.x = t2.y;

The sub query is evaluated, distinct’ed, indexed (or hashed or sorted) and then joined to

the original table — typically. As opposed to select * from t1 where exists ( select null

from t2 where y = x )

That is processed more like:

for x in ( select * from t1 )

loop

if ( exists ( select null from t2 where y = x.x )

then

OUTPUT THE RECORD

end if

end loop

It always results in a full scan of T1 whereas the first query can make use of an index on

T1(x). So, when is where exists appropriate and in appropriate? Lets say the result of the

sub query ( select y from T2 ) is “huge” and takes a long time. But the table T1 is

relatively small and executing ( select null from t2 where y = x.x ) is very fast (nice index

on t2(y)). Then the exists will be faster as the time to full scan T1 and do the index probe

into T2 could be less then the time to simply full scan T2 to build the sub query we need

to distinct on.

Lets say the result of the sub query is small — then IN is typically more appropriate. If

both the sub query and the outer table are huge — either might work as well as the other

—     depends on the indexes and other factors.

When do you use WHERE clause and when do you use HAVING clause?

The WHERE condition lets you restrict the rows selected to those that satisfy one or more

conditions. Use the HAVING clause to restrict the groups of returned rows to those

groups for which the specified condition is TRUE.

There is a % sign in one field of a column. What will be the query to find it?

SELECT column_name FROM table_name WHERE column_name LIKE ‘%%%’

ESCAPE ‘’;

Where will you find forms configuration details apart from xml file ?

Forms configuration at time of startup is in script adfrmctl.sh and

appsweb_$CONTEXT_NAME.cfg (defined by environment variable

FORMS60_WEB_CONFIG_FILE) for forms client connection used each time a user

initiates forms connection.

What is forms server executable Name ?

f60srvm

What are different modes of forms in which you can start Forms Server and which

one is default ?

You can start forms server in SOCKET or SERVLET by defualt Forms are configured to

start in socket mode.

How you will start Discoverer in Oracle Apps 11i ?

In order to start dicoverer you can use script addisctl.sh under

$OAD_TOP/admin/scripts/$CONTEXT_NAME or startall.sh under

$ORACLE_HOME/discwb4/util (under Middle/Application Tier)

How many ORACLE HOME are Oracle Apps and whats significance of each ?

There are three $ORACLE_HOME in Oracle Apps, Two for Application Tier (Middle

Tier) and One in Database Tier.

# ORACLE_HOME 1 : On Application Tier used to store 8.0.6 techstack software. This

is used by forms, reports and discoverer. ORACLE_HOME should point to this

ORACLE_HOME which applying Apps Patch.

# ORACLE_HOME 2: On Application Tier used by iAS (Web Server) techstack

software. This is used by Web Listener and contains Apache.

# ORACLE_HOME 3: On Database Tier used by Database Software usually 8i,9i or 10g

database.

Where is HTML Cache stored in Oracle Apps Server ?

Oracle HTML Cache is available at $COMMON_TOP/_pages for some previous

versions you might find it in $OA_HTML/_pages

Where is plssql cache stored in Oracle Apps ?

Usually two type of cache session and plssql stored under

$IAS_ORACLE_HOME/Apache/modplsql/cache

What happens if you don’t give cache size while defining Concurrent Manager ?

Lets first understand what is cache size in Concurrent Manager. When Manager picks

request from FND CONCURRENT REQUESTS Queues, it will pick up number of

requests defined by cache size in one shot and will work on them before going to sleep. If

you don’t define cache size while defining CM then it will take default value 1, i.e.

picking up one request per cycle.

There are lot of DBC file under $FND_SECURE, How its determined that which

dbc file to use from $FND_SECURE ?

This value is determined from profile option “Applications Database ID”

What is RRA/FNDFS ?

Report Review Agent(RRA) also referred by executable FNDFS is default text viewer in

Oracle Applications 11i for viewing output files and log files. As most of apps dba’s are

not clear about Report Server and RRA, I’ll discuss one on my blog and update link here .

What is PCP is Oracle Applications 11i ?

PCP is acronym for Parallel Concurrurent processing. Usually you have one Concurrent

Manager executing your requests but if you can configure Concurrent Manager running

on two machines (Yes you need to do some additional steps in order to configure Parallel

Concurrent Processing) . So for some of your requests primary CM Node is on machine1

and secondary CM node on machine2 and for some requests primary CM is on machine2

and secondary CM on machine1.

Why I need two Concurrent Processing Nodes or in what scenarios PCP is Used ?

Well If you are running GL Month end reports or taxation reports annually these reposrts

might take couple of days. Some of these requests are very resource intensive so you can

have one node running long running , resource intensive requests while other processing

your day to day short running requets.

Another scenario is when your requests are very critical and you want high resilience for

your Concurrent Processing Node , you can configure PCP. So if node1 goes down you

still have CM node available processing your requests.

Output and Logfiles for requests executed on source Instance not working on cloned

Instance

Here is exact problem description – You cloned an Oracle Apps Instance from

PRODBOX to another box with Instance name say CLONEBOX on 1st of August. You

can any CM logs/output files after 1st of August only becuase these all are generated on

CLONEBOX itself, But unable to view the logs/output files which are prior to 1st

August. What will you do and where to check ?

Log , Output file path and location is stored in table

FND_CONCURRENT_REQUESTS. Check select logfile_name, logfile_node_name,

outfile_name, outfile_node_name from fnd_concurrent_requests where

request_id=&requestid ; where requestid is id of request for which you are not able to see

log or out files. You should see output like /u01/PRODBOX/log/l123456.req,

host1,/u01/PRODBOX/out/o123456.out, host1

Update it according to your cloned Instance Variables.

How to confirm if Report Server is Up and Running ?

Report Server is started by executable rwmts60 on concurrent manager Node and this file

is under $ORACLE_HOME/bin .execute command on your server like

ps -ef | grep rwmts60

You should get output like

applmgr ……. rwmts60

What is difference between ICM, Standard Managers and CRM in Concurrent

Manager ?

# ICM stand for Internal Concurrent Manager, which controls other managers. If it finds

other managers down , it checks and try to restart them. You can say it as administrator to

other concurrent managers. It has other tasks as well.

# Standard Manager These are normal managers which control/action on the requests nd

does batch or single request processing. # CRM acronym for Conflict Resolution

Manager is used to resolve conflicts between managers nd request. If a request is

submitted whose execution is clashing or it is defined not to run while a particular type of

request is running then such requests are actioned/assigned to CRM for Incompatibilities

and Conflict resolution.

What is difference between SUBSTR and INSTR?

INSTR function search string for sub-string and returns an integer indicating the position

of the character in string that is the first character of this occurrence. SUBSTR function

return a portion of string, beginning at character position, substring_length characters

long. SUBSTR calculates lengths using characters as defined by the input character set.

Which data type is used for storing graphics and images?

Raw, Long Raw, and BLOB.

What is difference between SQL and SQL*PLUS?

SQL is the query language to manipulate the data from the database. SQL*PLUS is the

tool that lets to use SQL to fetch and display the data.

What is difference between UNIQUE and PRIMARY KEY constraints?

An UNIQUE key can have NULL whereas PRIMARY key is always not NOT NULL.

Both bears unique values.

What is difference between Rename and Alias?

Rename is actually changing the name of an object whereas Alias is giving another name

(additional name) to an existing object.

Rename is a permanent name given to a table or column whereas Alias is a temporary

name given to a table or column which do not exist once the SQL statement is executed.

What are various joins used while writing SUBQUERIES?

=, , IN, NOT IN, IN ANY, IN ALL, EXISTS, NOT EXISTS.

What is use of Apps listener ?

Apps Listener usually running on All Oracle Applications 11i Nodes with listener alias as

APPS_$SID is mainly used for listening requests for services like FNDFS and FNDSM.

How to start Apps listener ?

In Oracle 11i, you have script adalnctl.sh which will start your apps listener. You can also

start it by command lsnrctl start APPS_$SID (Replace sid by your Instance SID Name)

How to confirm if Apps Listener is Up and Running ?

execute below command

lsnrctl status APPS_$SID (replcae SID with your Instance Name)

so If your SID is VISION then use lsnrctl status APPS_VISION out put should be like

Services Summary…

FNDFS has 1 service handler(s)

FNDSM has 1 service handler(s)

What is Web Listener ?

Web Listener is Web Server listener which is listening for web Services(HTTP) request.

This listener is started by adapcctl.sh and defined by directive (Listen, Port) in httpd.conf

for Web Server. When you initially type request like

http://becomeappsdba.blogspot.com:80 to access application here port number 80 is Web

Listener port.

How will you find Invalid Objects in database ?

using query SQLPLUS> select count(*) from dba_objects where status like ‘INVALID’;

How to compile Invalid Objects in database ?

You can use adadmin utility to compile or you can use utlrp.sql script shipped with

Oracle Database to compile Invalid Database Objects.

How to compile JSP in Oracle Apps ?

You can use ojspCompile.pl perl script shipped with Oracle apps to compile JSP files.

This script is under $JTF_TOP/admin/scripts. Sample compilation method is

perl ojspCompile.pl –compile –quiet

What is difference between ADPATCH and OPATCH ?

# ADPATCH is utility to apply oracle apps Patches whereas

# OPATCH is utility to apply database patches

Can you use both ADPATCH and OPATCH in Apps ?

Yes you have to use both in apps , for apps patches you will use ADPATCH UTILITY

and for applying database patch in apps you will use opatch UTILITY.

Oracle DBA interview questions

Oracle Concepts and Architecture Database Structures

1. What are the components of physical database structure of Oracle database?

Physical Structure

The physical layer of the database consists of three types of files:

  1. One or more Datafiles
  2. Two or more redo log files
  3. One or more control files

Datafiles (.dbf files):

Datafiles store the information contained in the database. One can have as few as one data file or as many as hundreds of datafiles. The information for a single table can span many datafiles or many tables can share a set of datafiles. Spreading tablespaces over many datafiles can have a significant positive effect on performance. The number of datafiles that can be configured is limited by the Oracle parameter MAXDATAFILES.

Redo Log Files (.rdo & .arc):

Oracle maintains logs of all the transaction against the database. These transactions are recorded in files called Online Redo Log Files (Redo Logs). The main purpose of the Redo log files is to hold information as recovery in the event of a system failure. Redo log stores a log of all changes made to the database. The redo log files must perform well and be protected against hardware failures (through software or hardware fault tolerance). If redo log information is lost, one cannot recover the system.

When a transaction occurs in the database, it is entered in the redo log buffers, while the data blocks affected by the transactions are not immediately written to disk. In anOracle database there are at least three or more Redo Log files.

Oracle writes to redo log file in a cyclical order i.e. after the first log file is filled, it writes to the second log file, until that one is filled. When all the Redo Log files have been filled, it returns to the first log file and begin overwrite its content with new transaction data. Note, if the database is running in the ARCHIVELOG Mode, the database will make a copy of the online redo log files before overwriting them.

Control Files (.ctl):

Control files record control information about all of the files within the database. These files maintain internal consistency and guide recovery operation. Control files contain information used to start an instance, such as the location of datafiles and redo log files; Oracle needs this information to start the database instance. Control files must be protected. Oracle provides a mechanism for storing multiple copies of control files. These multiple copies are stored on separate disks to minimize the potential damage due to disk failure. The names of the database’s control files are specified via the CONTROL_FILES initialization parameter.

2. What are the components of logical database structure of Oracle database?

Oracle is an RDBMS (Relational Database Management System). The Oracle database architecture can be described in terms of logical and physical structures. The advantage of separating the logical and physical structure is that the physical storage structure can be changed without affecting the logical structure.

Logical Structure

The logical structure for Oracle RDBMS consists of the following elements:

  • Tablespace
  • Schema

Tablespace

The Oracle database consists of one or more logical portions called as ‘Tablespaces’. A tablespace is a logical grouping of related data.

A database administrator can use Tablespaces to do the following:

  • Control disk space allocation for database data.
  • Assign specific space quotas for database users.
  • Perform partial database backup or recovery operations.
  • Allocate data storage across devices to improve performance.

Each database has at least one Tablespace called SYSTEM Tablespace. As part of the process of creating the database, Oracle automatically creates the SYSTEM tablespace. Although a small database can fit within the SYSTEM tablespace, it’s recommended that to create a separate tablespace for user data.

Oracle uses the SYSTEM tablespace to store information like the data dictionary. Data dictionary stores the metadata (or the data about data). This includes information like table access permissions, information about keys etc.

Data is stored in the database in form of files called as datafiles. Each Tablespace is a collection of one or more Datafiles. Each data file consists of ‘Data blocks’, ‘extents’ and ‘segments’.

Data Blocks

At the finest level of granularity, an ORACLE database’s data is stored in data blocks (also called logical blocks, ORACLE blocks, or pages). An ORACLE database uses and allocates free database space in ORACLE data blocks.

Extents

The next level of logical database space is called an extent. An extent is a specific number of contiguous data blocks that are allocated for storing a specific type of information.

Segments

The level of logical database storage above an extent is called a segment. A segment is a set of extents that have been allocated for a specific type of data structure, and all are stored in the same tablespace. For example, each table’s data is stored in its own data segment, while each index’s data is stored in its own index segment. ORACLE allocates space for segments in extents. Therefore, when the existing extents of a segment are full, ORACLE allocates another extent for that segment. Because extents are allocated as needed, the extents of a segment may or may not be contiguous on disk, and may or may not span files.

An Oracle database can use four types of segments:

  • Data segment–Stores user data within the database.
  • Index segment–Stores indexes.
  • Rollback segment–Stores rollback information. This information is used when data must be rolled back.
  • Temporary segment–Created when a SQL statement needs a temporary work area; these segments are destroyed when the SQL statement is finished. These segments are used during various database operations, such as sorts.

Schema

The database schema is a collection of logical-structure objects, known as schema objects that define how you see the database’s data. A schema also defines a level of access for the users. All the logical objects in oracle are grouped into a schema.

A scheme is a logical grouping of objects such as:

  • Tables
  • Clusters
  • Indexes
  • Views
  • Stored procedures
  • Triggers
  • Sequences

3. What is a tablespace?

A tablespace is a logical storage unit within an Oracle database. It is logical because a tablespace is not visible in the file system of the machine on which the database resides. A tablespace, in turn, consists of at least one datafile which, in turn, are physically located in the file system of the server. Btw, a datafile belongs to exactly one tablespace.

Each table, index and so on that is stored in an Oracle database belongs to a tablespace. The tablespace builds the bridge between the Oracle database and the filesystem in which the table’s or index’ data is stored.

There are three types of tablespaces in Oracle:

A tablespace is created with the create tablespace sql command.

See adding tablespaces to primary servers if you want to add a tablespace to a primary server in a standby environment.

Dropping a tablespace

Dropping a tablespace is a structural change to the database that requires a backup.

The extent size of the objects in the tablespace are subject to the tablespace’s minimum extent size.

Quotas on tablespaces

Users can have (space) quotas on tablespaces. This is a means to limit how much space a user uses on a tablespace. This quota can be set using alter user quota…

Tablespace groups

This is a feature that is available with Oracle 10g.

Assigning a tablespace to a tablespace group:

alter tablespace ts_user tablespace group ts_grp_user;

Renaming Tablespaces

This is a feature that is available with Oracle 10g and can be useful in transportable tablespace scenarios.

alter tablespace ts_user rename to ts_user_01;

The system and sysaux tablespace cannot be renamed, though. But that will not be much of a problem, will it? However, read only tablespaces can be renamed.

After renaming a tablespace, the controlfiles should immediatly be backed up.

The system tablespace

The system tablespace is always available when a database is open (it cannot be taken offline).

The system tablespace stores the data dictionary (or their base tables, respectively).

The sysaux tablespace

The sysaux tablespace is new with Oracle 10g. It is used to store database components that were stored in the system tablespace in prior releases of the database.
Also, the tablespaces that were needed for RMAN’s recovery catalog, for Ultra Search, for Data Mining, for XDP and for OLAP are going to sysaux with 10g.
Additionally, it is the place where automatic workload repository stores its information.

occupants

An occupant is a set of (application-) tables within the sysaux tablespace. The occupants can be viewed with the v$sysaux_occupants

Transportable tablespaces

See transportable tablespaces

Bigfile tablespaces

This is a feature of Oracle 10g. A bigfile tablespace contains only one datafile (or tempfile) which can be as big as 2^32 (=4GB) blocks.

create bigfile tablespace beeeg_ts data file '/o1/dat/beeeg.dbf' size 2T

Bigfile tablespaces are supported only for locally managed tablespaces with automatic segment-space management (which is the default setting since Oracle 9i). There are two exceptions: locally managed undo and temporary tablespaces can be bigfile tablespaces, even though their segments are manually managed.

The system and sysaux tablespace cannot be created as bigfile tablespace.

Bigfile tablespaces should be used with automatic storage management, or other logical volume managers that support dynamically extensible logical volumes, striping and RAID.

Smallfile tablespaces

A smallfile tablespace is a traditional tablespace that can contain up to 1022 datafiles.

Default tablespaces

An Oracle database can be configured with a default tablespace and a default temporary tablespace. These are used for users who are not configured with default tablespaces or default temporary tablespaces.

Displaying tablespaces

The dba_tablespaces view displays all tablespaces along with the respective relevant information.

Space management

Oracle maintains extents for a tablespace. There are two different methods for Oracle to keep track of free and used (occupied) extents:

It’s not possible to alter the space allocation method of a tablespace after it has been created. (Update 10g R2: it seems that is now possible with dbms_space_admin.)

Dictionary managed tablespaces

Extents are allocated according to the following storage parameters

  • initial
  • next
  • pctincrease

The information about used and free extents is stored in the dictionary.

Locally managed tablespaces

A ‘bitmap’ is stored within the tablespace. Each bit within this bitmap determines if a corresponding extent in the tablespace is free or used.

The extent sizes are either uniform or autoallocate. Hence, the following storage parameters don’t make sense and are not permitted:

  • next
  • pctincrease
  • minextents
  • maxextents
  • default storage

Locally managed tablespaces have two advantages: recursive space management is avoided and adjacent free space is automatically coalesced.

Tablespace count limits

As per 10g, a database cannot have more than 65536 tablespaces. See also datafile count limits.

A bigfile tablespace can address 4294967296 (or 232) db blocks. A smallfile tablespace can address 4194304 (or 222) db blocks.

State of tablespaces

A tablespace is either online (ready to be accessed) or offline (not accessible).

A tablespace becomes offline either

  • when the DBA explicitely makes the tablespace offline, or
  • when an error occures while Oracle accesses a datafile within the tablespace.

Offline tablespaces cannot be transported to other databases.

Read Only Tablespaces

Read only tablespaces have the benefit that they need be backed up only once.

4. What is SYSTEM tablespace and when is it created?

Every Oracle database contains a tablespace named SYSTEM, which is automatically created when the database is created. The SYSTEM tablespace always contains the data dictionary tables for the entire database.

5. Explain the relationship among database, tablespace and data file.?

Each databases logically divided into one or more tablespaces one or more data files are explicitly created for each tablespace.

6. What is schema?

A schema is collection of database objects of a User.

7. What are Schema Objects?

Schema objects are the logical structures that directly refer to the database’s data. Schema bjects include tables, views, sequences, synonyms, indexes, clusters, database triggers, procedures, functions packages and database links.

8. Can objects of the same schema reside in different tablespaces?

Yes

9. Can a tablespace hold objects from different schemes?

Yes

10. What is Oracle table?

A table is the basic unit of data storage in an Oracle database. The tables of a database hold all of the user accessible data. Table data is stored in rows and columns.

11. What is an Oracle view?

A view is a virtual table. Every view has a query attached to it. (The query is a SELECT statement that identifies the columns and rows of the table(s) the view uses.)

A View in Oracle and in other database systems is simply the representation of a SQL statement that is stored in memory so that it can easily be re-used. For example, if we frequently issue the following query

SELECT customerid, customername FROM customers WHERE countryid='US';

To create a view use the CREATE VIEW command as seen in this example

CREATE VIEW view_uscustomers
AS
SELECT customerid, customername FROM customers WHERE countryid='US';

This command creates a new view called view_uscustomers. Note that this command does not result in anything being actually stored in the database at all except for a data dictionary entry that defines this view. This means that every time you query this view, Oracle has to go out and execute the view and query the database data. We can query the view like this:

SELECT * FROM view_uscustomers WHERE customerid BETWEEN 100 AND 200;

And Oracle will transform the query into this:

SELECT * 
FROM (select customerid, customername from customers WHERE countryid='US') 
WHERE customerid BETWEEN 100 AND 200

12. Do a view contain data?

Views do not contain or store data.

13. Can a view based on another view?

Yes

14. What are the advantages of views?

– Provide an additional level of table security, by restricting access to a predetermined set

of rows and columns of a table.

– Hide data complexity.

– Simplify commands for the user.

– Present the data in a different perspective from that of the base table.

– Store complex queries.

15. What is an Oracle sequence?

A sequence generates a serial list of unique numbers for numerical columns of a

database’s tables.

16. What is a synonym?

A synonym is an alias for a table, view, sequence or program unit.

17. What are the types of synonyms?

There are two types of synonyms private and public.

18. What is a private synonym?

Only its owner can access a private synonym.

19. What is a public synonym?

Any database user can access a public synonym.

20. What are synonyms used for?

– Mask the real name and owner of an object.

– Provide public access to an object

– Provide location transparency for tables, views or program units of a remote database.

– Simplify the SQL statements for database users.

21. What is an Oracle index?

An index is an optional structure associated with a table to have direct access to rows,

which can be created to increase the performance of data retrieval. Index can be created

on one or more columns of a table.

22. How are the index updates?

Indexes are automatically maintained and used by Oracle. Changes to table data are

automatically incorporated into all relevant indexes.

23. What are clusters?

Clusters are groups of one or more tables physically stores together to share common

columns and are often used together.

24. What is cluster key?

The related columns of the tables in a cluster are called the cluster key.

25. What is index cluster?

A cluster with an index on the cluster key.

26. What is hash cluster?

A row is stored in a hash cluster based on the result of applying a hash function to the

row’s cluster key value. All rows with the same hash key value are stores together on

disk.

27. When can hash cluster used?

Hash clusters are better choice when a table is often queried with equality queries. For

such queries the specified cluster key value is hashed. The resulting hash key value points

directly to the area on disk that stores the specified rows.

28. What is database link?

A database link is a named object that describes a “path” from one database to another.

29. What are the types of database links?

Private database link, public database link & network database link.

30. What is private database link?

Private database link is created on behalf of a specific user. A private database link can be

used only when the owner of the link specifies a global object name in a SQL statement

or in the definition of the owner’s views or procedures.

31. What is public database link?

Public database link is created for the special user group PUBLIC. A public database link

can be used when any user in the associated database specifies a global object name in a

SQL statement or object definition.

32. What is network database link?

Network database link is created and managed by a network domain service. A network

database link can be used when any user of any database in the network specifies a global

object name in a SQL statement or object definition.

33. What is data block?

Oracle database’s data is stored in data blocks. One data block corresponds to a specific

number of bytes of physical database space on disk.

34. How to define data block size?

A data block size is specified for each Oracle database when the database is created. A

database users and allocated free database space in Oracle data blocks. Block size is

specified in init.ora file and cannot be changed latter.

35. What is row chaining?

In circumstances, all of the data for a row in a table may not be able to fit in the same

data block. When this occurs, the data for the row is stored in a chain of data block (one

or more) reserved for that segment.

36. What is an extent?

An extent is a specific number of contiguous data blocks, obtained in a single allocation

and used to store a specific type of information.

37. What is a segment?

A segment is a set of extents allocated for a certain logical structure.

38. What are the different types of segments?

Data segment, index segment, rollback segment and temporary segment.

39. What is a data segment?

Each non-clustered table has a data segment. All of the table’s data is stored in the extents

of its data segment. Each cluster has a data segment. The data of every table in the cluster

is stored in the cluster’s data segment.

40. What is an index segment?

Each index has an index segment that stores all of its data.

41. What is rollback segment?

A database contains one or more rollback segments to temporarily store “undo”

information.

42. What are the uses of rollback segment?

To generate read-consistent database information during database recovery and to

rollback uncommitted transactions by the users.

43. What is a temporary segment?

Temporary segments are created by Oracle when a SQL statement needs a temporary

work area to complete execution. When the statement finishes execution, the temporary

segment extents are released to the system for future use.

44. What is a datafile?

Every Oracle database has one or more physical data files. A database’s data files contain

all the database data. The data of logical database structures such as tables and indexes is

physically stored in the data files allocated for a database.

45. What are the characteristics of data files?

A data file can be associated with only one database. Once created a data file can’t change

size. One or more data files form a logical unit of database storage called a tablespace.

46. What is a redo log?

The set of redo log files for a database is collectively known as the database redo log.

47. What is the function of redo log?

The primary function of the redo log is to record all changes made to data.

48. What is the use of redo log information?

The information in a redo log file is used only to recover the database from a system or

media failure prevents database data from being written to a database’s data files.

49. What does a control file contains?

– Database name

– Names and locations of a database’s files and redolog files.

– Time stamp of database creation.

50. What is the use of control file?

When an instance of an Oracle database is started, its control file is used to identify the

database and redo log files that must be opened for database operation to proceed. It is

also used in database recovery.

Data Base Administration

51. What is a database instance? Explain.

A database instance (Server) is a set of memory structure and background processes that

access a set of database files. The processes can be shared by all of the users.

The memory structure that is used to store the most queried data from database. This

helps up to improve database performance by decreasing the amount of I/O performed

against data file.

52. What is Parallel Server?

Multiple instances accessing the same database (only in multi-CPU environments)

53. What is a schema?

The set of objects owned by user account is called the schema.

54. What is an index? How it is implemented in Oracle database?

An index is a database structure used by the server to have direct access of a row in a

table. An index is automatically created when a unique of primary key constraint clause is

specified in create table command

55. What are clusters?

Group of tables physically stored together because they share common columns and are

often used together is called cluster.

56. What is a cluster key?

The related columns of the tables are called the cluster key. The cluster key is indexed

using a cluster index and its value is stored only once for multiple tables in the cluster.

57. What are the basic element of base configuration of an Oracle database?

It consists of

one or more data files.

one or more control files.

two or more redo log files.

The Database contains

multiple users/schemas

one or more rollback segments

one or more tablespaces

Data dictionary tables

User objects (table,indexes,views etc.,)

The server that access the database consists of

SGA (Database buffer, Dictionary Cache Buffers, Redo log buffers, Shared SQL

pool)

SMON (System MONito)

PMON (Process MONitor)

LGWR (LoG Write)

DBWR (Data Base Write)

ARCH (ARCHiver)

CKPT (Check Point)

RECO

Dispatcher

User Process with associated PGS

58. What is a deadlock? Explain.

Two processes waiting to update the rows of a table, which are locked by other processes

then deadlock arises.

In a database environment this will often happen because of not issuing the proper row

lock commands. Poor design of front-end application may cause this situation and the

performance of server will reduce drastically.

These locks will be released automatically when a commit/rollback operation performed

or any one of this processes being killed externally.

Memory Management

59. What is SGA?

The System Global Area in an Oracle database is the area in memory to facilitate the

transfer of information between users. It holds the most recently requested structural

information between users. It holds the most recently requested structural information

about the database. The structure is database buffers, dictionary cache, redo log buffer

and shared pool area.

60. What is a shared pool?

The data dictionary cache is stored in an area in SGA called the shared pool. This will

allow sharing of parsed SQL statements among concurrent users.

61. What is mean by Program Global Area (PGA)?

It is area in memory that is used by a single Oracle user process.

62. What is a data segment?

Data segment are the physical areas within a database block in which the data associated

with tables and clusters are stored.

63. What are the factors causing the reparsing of SQL statements in SGA?

Due to insufficient shared pool size.

Monitor the ratio of the reloads takes place while executing SQL statements. If the ratio

is greater than 1 then increase the SHARED_POOL_SIZE.

Database Logical & Physical Architecture

64. What is Database Buffers?

Database buffers are cache in the SGA used to hold the data blocks that are read from the

data segments in the database such as tables, indexes and clusters

DB_BLOCK_BUFFERS parameter in INIT.ORA decides the size.

65. What is dictionary cache?

Dictionary cache is information about the database objects stored in a data dictionary

table.

66. What is meant by recursive hints?

Number of times processes repeatedly query the dictionary table is called recursive hints.

It is due to the data dictionary cache is too small. By increasing the

SHARED_POOL_SIZE parameter we can optimize the size of data dictionary cache.

67. What is redo log buffer?

Changes made to the records are written to the on-line redo log files. So that they can be

used in roll forward operations during database recoveries. Before writing them into the

redo log files, they will first brought to redo log buffers in SGA and LGWR will write

into files frequently. LOG_BUFFER parameter will decide the size.

68. How will you swap objects into a different table space for an existing database?

– Export the user

– Perform import using the command imp system/manager file=export.dmp

indexfile=newrite.sql. This will create all definitions into newfile.sql.

– Drop necessary objects.

– Run the script newfile.sql after altering the tablespaces.

– Import from the backup for the necessary objects.

69. List the Optional Flexible Architecture (OFA) of Oracle database? How can we

organize the tablespaces in Oracle database to have maximum performance?

SYSTEM – Data dictionary tables.

DATA – Standard operational tables.

DATA2- Static tables used for standard operations

INDEXES – Indexes for Standard operational tables.

INDEXES1 – Indexes of static tables used for standard operations.

TOOLS – Tools table.

TOOLS1 – Indexes for tools table.

RBS – Standard Operations Rollback Segments,

RBS1,RBS2 – Additional/Special Rollback segments.

TEMP – Temporary purpose tablespace

TEMP_USER – Temporary tablespace for users.

USERS – User tablespace.

70. How will you force database to use particular rollback segment?

SET TRANSACTION USE ROLLBACK SEGMENT rbs_name.

71. What is meant by free extent?

A free extent is a collection of continuous free blocks in tablespace. When a segment is

dropped its extents are reallocated and are marked as free.

72.Which parameter in Storage clause will reduce number of rows per block?

PCTFREE parameter

Row size also reduces no of rows per block.

73. What is the significance of having storage clause?

We can plan the storage for a table as how much initial extents are required, how much

can be extended next, how much % should leave free for managing row updating, etc.,

74. How does Space allocation table place within a block?

Each block contains entries as follows

Fixed block header

Variable block header

Row Header, row date (multiple rows may exists)

PCTEREE (% of free space for row updating in future)

75. What is the role of PCTFREE parameter is storage clause?

This is used to reserve certain amount of space in a block for expansion of rows.

76. What is the OPTIMAL parameter?

It is used to set the optimal length of a rollback segment.

77. What is the functionality of SYSTEM table space?

To manage the database level transactions such as modifications of the data dictionary

table that record information about the free space usage.

78. How will you create multiple rollback segments in a database?

– Create a database, which implicitly creates a SYSTEM rollback segment in a SYSTEM

tablespace.

– Create a second rollback segment name R0 in the SYSTEM tablespace.

– Make new rollback segment available (after shutdown, modify init.ora file and start

database)

– Create other tablespaces (RBS) for rollback segments.

– Deactivate rollback segment R0 and activate the newly created rollback segments.

79. How the space utilization takes place within rollback segments?

It will try to fit the transaction in a cyclic fashion to all existing extents. Once it found an

extent is in use then it forced to acquire a new extent (number of extents is based on the

optimal size)

80. Why query fails sometimes?

Rollback segment dynamically extent to handle larger transactions entry loads.

A single transaction may wipeout all available free space in the rollback segment

tablespace. This prevents other user using rollback segments.

81. How will you monitor the space allocation?

By querying DBA_SEGMENT table/view

82. How will you monitor rollback segment status?

Querying the DBA_ROLLBACK_SEGS view

IN USE – Rollback Segment is on-line.

AVAILABLE – Rollback Segment available but not on-line.

OFF-LINE – Rollback Segment off-line

INVALID – Rollback Segment Dropped.

NEEDS RECOVERY – Contains data but need recovery or corrupted.

PARTLY AVAILABLE – Contains data from an unresolved transaction involving a

distributed database.

83. List the sequence of events when a large transaction that exceeds beyond its

optimal value when an entry wraps and causes the rollback segment to expand into

another extend.

Transaction Begins.

An entry is made in the RES header for new transactions entry

Transaction acquires blocks in an extent of RBS

The entry attempts to wrap into second extent. None is available, so that the RBS must

extent.

The RBS checks to see if it is part of its OPTIMAL size.

RBS chooses its oldest inactive segment.

Oldest inactive segment is eliminated.

RBS extents

The data dictionary tables for space management are updated.

Transaction Completes.

84. How can we plan storage for very large tables?

Limit the number of extents in the table

Separate table from its indexes.

Allocate sufficient temporary storage.

85. How will you estimate the space required by a non-clustered tables?

Calculate the total header size

Calculate the available data space per data block

Calculate the combined column lengths of the average row

Calculate the total average row size.

Calculate the average number rows that can fit in a block

Calculate the number of blocks and bytes required for the table.

After arriving the calculation, add 10 % additional space to calculate the initial extent

size for a working table.

86. It is possible to use raw devices as data files and what are the advantages over

file system files?

Yes.

The advantages over file system files are that I/O will be improved because Oracle is

bye-passing the kernel which writing into disk. Disk corruption will be very less.

87. What is a Control file?

Database’s overall physical architecture is maintained in a file called control file. It will

be used to maintain internal consistency and guide recovery operations. Multiple copies

of control files are advisable.

88. How to implement the multiple control files for an existing database?

Shutdown the database

Copy one of the existing controlfile to new location

Edit Config ora file by adding new control filename

Restart the database.

89. What is redo log file mirroring? How can be achieved?

Process of having a copy of redo log files is called mirroring.

This can be achieved by creating group of log files together, so that LGWR will

automatically writes them to all the members of the current on-line redo log group. If any

one group fails then database automatically switch over to next group. It degrades

performance.

90. What is advantage of having disk shadowing / mirroring?

Shadow set of disks save as a backup in the event of disk failure. In most operating

systems if any disk failure occurs it automatically switchover to place of failed disk.

Improved performance because most OS support volume shadowing can direct file I/O

request to use the shadow set of files instead of the main set of files. This reduces I/O

load on the main set of disks.

91. What is use of rollback segments in Oracle database?

They allow the database to maintain read consistency between multiple transactions.

92. What is a rollback segment entry?

It is the set of before image data blocks that contain rows that are modified by a

transaction.

Each rollback segment entry must be completed within one rollback segment.

A single rollback segment can have multiple rollback segment entries.

93. What is hit ratio?

It is a measure of well the data cache buffer is handling requests for data.

Hit Ratio = (Logical Reads – Physical Reads – Hits Misses)/ Logical Reads.

94. When will be a segment released?

When Segment is dropped.

When Shrink (RBS only)

When truncated (TRUNCATE used with drop storage option)

95. What are disadvantages of having raw devices?

We should depend on export/import utility for backup/recovery (fully reliable)

The tar command cannot be used for physical file backup, instead we can use dd

command, which is less flexible and has limited recoveries.

96. List the factors that can affect the accuracy of the estimations?

– The space used transaction entries and deleted records, does not become free

immediately after completion due to delayed cleanout.

– Trailing nulls and length bytes are not stored.

– Inserts of, updates to and deletes of rows as well as columns larger than a single data

block, can cause fragmentation a chained row pieces.

Database Security & Administration

97. What is user Account in Oracle database?

A user account is not a physical structure in database but it is having important

relationship to the objects in the database and will be having certain privileges.

98. How will you enforce security using stored procedures?

Don’t grant user access directly to tables within the application.

Instead grant the ability to access the procedures that access the tables.

When procedure executed it will execute the privilege of procedures owner. Users cannot

access tables except via the procedure.

99. What are the dictionary tables used to monitor a database space?

DBA_FREE_SPACE

DBA_SEGMENTS

DBA_DATA_FILES.

SQL*Plus Statements

100. What are the types of SQL statement?

Data Definition Language: CREATE, ALTER, DROP, TRUNCATE, REVOKE, NO

AUDIT & COMMIT.

Data Manipulation Language: INSERT, UPDATE, DELETE, LOCK TABLE, EXPLAIN

PLAN & SELECT.

Transactional Control: COMMIT & ROLLBACK

Session Control: ALTERSESSION & SET ROLE

System Control: ALTER SYSTEM.

101. What is a transaction?

Transaction is logical unit between two commits and commit and rollback.

102. What is difference between TRUNCATE & DELETE?

TRUNCATE commits after deleting entire table i.e., cannot be rolled back.

Database triggers do not fire on TRUNCATE

DELETE allows the filtered deletion. Deleted records can be rolled back or committed.

Database triggers fire on DELETE.

103. What is a join? Explain the different types of joins?

Join is a query, which retrieves related columns or rows from multiple tables.

Self Join – Joining the table with itself.

Equi Join – Joining two tables by equating two common columns.

Non-Equi Join – Joining two tables by equating two common columns.

Outer Join – Joining two tables in such a way that query can also retrieve rows that do not

have corresponding join value in the other table.

104. What is the sub-query?

Sub-query is a query whose return values are used in filtering conditions of the main

query.

105. What is correlated sub-query?

Correlated sub-query is a sub-query, which has reference to the main query.

106. Explain CONNECT BY PRIOR?

Retrieves rows in hierarchical order eg.

select empno, ename from emp where.

107. Difference between SUBSTR and INSTR?

INSTR (String1, String2 (n, (m)),

INSTR returns the position of the m-th occurrence of the string 2 in string1. The search

begins from nth position of string1.

SUBSTR (String1 n, m)

SUBSTR returns a character string of size m in string1, starting from n-th position of

string1.

108. Explain UNION, MINUS, UNION ALL and INTERSECT?

INTERSECT – returns all distinct rows selected by both queries.

MINUS – returns all distinct rows selected by the first query but not by the second.

UNION – returns all distinct rows selected by either query

UNION ALL – returns all rows selected by either query, including all duplicates.

109. What is ROWID?

ROWID is a pseudo column attached to each row of a table. It is 18 characters long,

blockno, rownumber are the components of ROWID.

110. What is the fastest way of accessing a row in a table?

Using ROWID.

CONSTRAINTS

111. What is an integrity constraint?

Integrity constraint is a rule that restricts values to a column in a table.

112. What is referential integrity constraint?

Maintaining data integrity through a set of rules that restrict the values of one or more

columns of the tables based on the values of primary key or unique key of the referenced

table.

113. What is the usage of SAVEPOINTS?

SAVEPOINTS are used to subdivide a transaction into smaller parts. It enables rolling

back part of a transaction. Maximum of five save points are allowed.

114. What is ON DELETE CASCADE?

When ON DELETE CASCADE is specified Oracle maintains referential integrity by

automatically removing dependent foreign key values if a referenced primary or unique

key value is removed.

115. What are the data types allowed in a table?

CHAR, VARCHAR2, NUMBER, DATE, RAW, LONG and LONG RAW.

116. What is difference between CHAR and VARCHAR2? What is the maximum

SIZE allowed for each type?

CHAR pads blank spaces to the maximum length.

VARCHAR2 does not pad blank spaces.

For CHAR the maximum length is 255 and 2000 for VARCHAR2.

117. How many LONG columns are allowed in a table? Is it possible to use LONG

columns in WHERE clause or ORDER BY?

Only one LONG column is allowed. It is not possible to use LONG column in WHERE

or ORDER BY clause.

118. What are the pre-requisites to modify datatype of a column and to add a

column with NOT NULL constraint?

– To modify the datatype of a column the column must be empty.

– To add a column with NOT NULL constrain, the table must be empty.

119. Where the integrity constraints are stored in data dictionary?

The integrity constraints are stored in USER_CONSTRAINTS.

120. How will you activate/deactivate integrity constraints?

The integrity constraints can be enabled or disabled by ALTER TABLE ENABLE

CONSTRAINT / DISABLE CONSTRAINT.

121. If unique key constraint on DATE column is created, will it validate the rows

that are inserted with SYSDATE?

It won’t, Because SYSDATE format contains time attached with it.

122. What is a database link?

Database link is a named path through which a remote database can be accessed.

123. How to access the current value and next value from a sequence? Is it possible

to access the current value in a session before accessing next value?

Sequence name CURRVAL, sequence name NEXTVAL. It is not possible. Only if you

access next value in the session, current value can be accessed.

124. What is CYCLE/NO CYCLE in a Sequence?

CYCLE specifies that the sequence continue to generate values after reaching either

maximum or minimum value. After pan-ascending sequence reaches its maximum value,

it generates its minimum value. After a descending sequence reaches its minimum, it

generates its maximum.

NO CYCLE specifies that the sequence cannot generate more values after reaching its

maximum or minimum value.

125. What are the advantages of VIEW?

– To protect some of the columns of a table from other users.

– To hide complexity of a query.

– To hide complexity of calculations.

126. Can a view be updated/inserted/deleted? If Yes – under what conditions?

A View can be updated/deleted/inserted if it has only one base table if the view is based

on columns from one or more tables then insert, update and delete is not possible.

127. If a view on a single base table is manipulated will the changes be reflected on

the base table?

If changes are made to the tables and these tables are the base tables of a view, then the

changes will be reference on the view.