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.

Advertisements
Previous Post
Leave a comment

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: