***** RAC Interview Questions *****

Q What is RAC?

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

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

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

Q Give the usage of srvctl ?

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

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

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

srvctl start database -d name [-o start_options]

srvctl stop database -d name [-o stop_options]

srvctl start database -d orcl -o mount

Q Mention the Oracle RAC software components ?

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

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


Q What is GRD?

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

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

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

Q Give Details on ACMS:

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

Q What is Cache Fusion?

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

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

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

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

Q What are the major RAC wait events?

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

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

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

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

Q Give details on GTX0-j 

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

Q Give details on LMON

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

Q Give details on LMD

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

Q Give details on LMS

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

Q Give details on LCK0

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

Q Give details on RMSn

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

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

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

for DBNAME in $(srvctl config database)
do

# Generate DB resource

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

# Generate Instance resource

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

# Modify instance for 10G – ASM dependency

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

echo “srvctl start database -d $DBNAME”

# Generate Service resource

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

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

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

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

Q Give details on RSMN

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

Q What components in RAC must reside in shared storage?

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

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

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

Q Give few examples for solutions that support cluster storage

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

Q What is an interconnect network?

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

Q How can we configure the cluster interconnect?

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

Q Can we use crossover cables with Oracle Clusterware interconnects?

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

Q What is the use of cluster interconnect?

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

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

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

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

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

Q What are the characteristics controlled by Oracle services feature?

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

Q What enables the load balancing of applications in RAC?

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

Q What is a virtual IP address or VIP?

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

Q What is the use of VIP?

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

Q Give situations under which VIP address failover happens

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

Q What is the significance of VIP address failover?

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

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

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

Q How do we verify that RAC instances are running?

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

Q What is FAN?

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

Q Where can we apply FAN UP and DOWN events?

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

Q Why should we have seperate homes for ASm instance?

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

Q What is the advantage of using ASM?

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

Q What is rolling upgrade?

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

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

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

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

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

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

RAC node name was listed in the loopback address…

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

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

Q Mention the components of Oracle clusterware

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

Q What is a CRS resource?

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

Q What is the use of OCR?

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

Q How does a Oracle Clusterware manage CRS resources?

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

Q Name some Oracle clusterware tools and their uses?

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Q What are the major RAC wait events?

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

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

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

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

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


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

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

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

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

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

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

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

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

A. Bring the datafile offline recover the datafile.

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


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


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

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

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

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

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

ocrconfig –showbackup

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

In 10.2

ocrconfig –export -s online

In 11g

ocrconfig -manualbackup

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

On one node as root run:

# ocrconfig -replace ocr
# ocrconfig -replace ocrmirror 

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

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

Note: crsctl votedisk commands must be run as root

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

crsctl query css votedisk

Take a backup of all voting disk:

dd if=voting_disk_name of=backup_file_name

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

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

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

# crsctl start crs

Verify the voting disk location using

crsctl query css votedisk

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

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

The Fixup script does the following:

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

including:

– Shared memory parameters.

– Open file descriptor and UDP send/receive parameters.

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

■ Reconfigures primary and secondary group memberships for the installation

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

privileges groups.

■ Sets shell limits if necessary to required values.

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

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

1. Invoke the Oracle Universal Installer (OUI)

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

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

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

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

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

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

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

– OCR and VD will be formated.

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

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

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

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

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

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

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

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

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

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

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

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

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

Q What are Oracle database background processes specific to RAC

•LMS—Global Cache Service Process

•LMD—Global Enqueue Service Daemon

•LMON—Global Enqueue Service Monitor

•LCK0—Instance Enqueue Process

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

Q What are Oracle Clusterware Components

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

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

Q How do you troubleshoot node reboot 

Please check metalink …

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

Q How do you backup the OCR

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

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

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

Q How do you backup voting disk

#dd if=voting_disk_name of=backup_file_name

Q How do I identify the voting disk location 

#crsctl query css votedisk

Q How do I identify the OCR file location 

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

Q Is ssh required for normal Oracle RAC operation ?

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

Q What is SCAN?

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

Click here for more details from Oracle

Q What is the purpose of Private Interconnect ?

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

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

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

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

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

Q How many nodes are supported in a RAC Database?

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

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

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

Q what is the purpose of the ONS daemon?

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

This in order to facilitate:

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

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

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

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

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

Q What are the characteristics controlled by Oracle services feature?

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

Q What is a voting disk?

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

Q What are the administrative tasks involved with voting disk?

Following administrative tasks are performed with the voting disk :

1) Backing up voting disks

2) Recovering Voting disks

3) Adding voting disks

4) Deleting voting disks

5) Moving voting disks

Q How do we backup voting disks?

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

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

crsctl query votedisk css

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

Give the syntax of backing up voting disks:-

On Linux or UNIX systems:

dd if=voting_disk_name of=backup_file_name

where,

voting_disk_name is the name of the active voting disk

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

On Windows systems, use the ocopy command:

ocopy voting_disk_name backup_file_name

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

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

Q How do you restore a voting disk?

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

On Linux or UNIX systems:

dd if=backup_file_name of=voting_disk_name

On Windows systems, use the ocopy command:

ocopy backup_file_name voting_disk_name

where,

backup_file_name is the name of the voting disk backup file

voting_disk_name is the name of the active voting disk

Q How can we add and remove multiple voting disks?

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

crsctl delete css votedisk path

crsctl add css votedisk path

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

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

Q How do we add voting disk?

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

crsctl add css votedisk path -force

Q How do we move voting disks?

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

crsctl delete css votedisk path -force

crsctl add css votedisk path -force

Q How do we remove voting disks?

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

crsctl delete css votedisk path -force

Q What should we do after modifying voting disks?

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

crsctl query css votedisk

Q When can we use -force option?

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

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