Real Application Cluster(RAC) Interview Questions Part 4

1.What is dynamic remastering? When will the dynamic remastering happens?

• Dynamic Remastering is ability to move the ownership of resource from one instance to another instance in RAC.
• Dynamic Resource remastering is used to implement for resource affinity for increased performance.
• Resource affinity optimized the system in situation where update transactions are being executed in one instance.
• When activity shift to another instance the resource affinity correspondingly move to another instance.
• If activity is not localized then resource ownership is hashed to the instance.

2.How you check the health of Your RAC Database?

‘crsctl’ command from Root or Oracle user can be used to check the clusterware health ,while for starting or stopping we have to use Root user or any privilege user.

$ crsctl check crs

3.If there is some issue with virtual IP how will you troubleshoot it?How will you change virtual ip?

To change the VIP (virtual IP) on a RAC node, use the command:

$ srvctl modify nodeapps -A new_address

4. 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, (i.e.) SGA updates are globally committed on success or globally aborted in event of a failure.

5.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 is 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.
• GC BUFFER BUSY is the time remote instance locally spends accessing the requested data block.

6. Give details on GTX0-j?

• This process provides transparent support for XA global transactions in a RAC environment.
• The database auto-tunes the number of these processes based on the workload of XA global transactions.

7.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.

8. Give details on LMD?

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

9. 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.

10. Give details on LCK0?

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

11. Give details on RMSn?

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

12. Give details on RSMN?

• This process is called as Remote Slave Monitor.
• This process manages background slave process creation and 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.

13. Can we use crossover cables with Oracle Clusterware interconnects?

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

14.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.

15. Why should we have separate homes for ASM instance?

• It is a good practice to have ASM home separate from the database home(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.

16. 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.

17.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.

18. 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).

19. 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