Oracle RAC Interview Questions

Here we are going to discussed oracle RAC interview questions, which are commonly asked by interviewers.

Best Oracle rac interview questions

Below you will find the best oracle RAC interview questions, I hope you will enjoy these questions.

Q1. What is Oracle RAC?

RAC stands for Real Application cluster. Oracle Real Application Clusters (RAC) allow customers to run a single Oracle Database across multiple servers in order to maximize availability and enable horizontal scalability while accessing shared storage.

Q2. What is cache fusion?

The Cache fusion is the mechanism to transfer the data block from memory to memory of one node to another node. If two nodes required the same block for query or update, the block must be transferred from the cache of one node to the other. RAC system must be equipped with low-latency and high-speed interconnect to make it happen.
Cache Fusion is a new technology that uses a high-speed interprocess communication (IPC) interconnect to provide cache to cache transfers of data blocks between instances in a cluster. This eliminates disk I/O (which is inherently slow, since it is a mechanical process) and optimizes read/write concurrency. 

Q3. What is a split-brain?

When database nodes in a cluster are unable to communicate with each other, they may continue to process and modify the data blocks independently. If the same block is modified by more than one instance, synchronization/locking of the data blocks does not take place and blocks may be overwritten by others in the cluster. This state is called split-brain.

Q4. What is the difference between Crash recovery and Instance recovery?

When an instance crashes in a single node database on startup a crash recovery takes place. In a RAC environment, the same recovery for an instance is performed by the surviving nodes called Instance recovery.

Q5. What is the interconnect used for?

It is a private network, which is used to ship data blocks from one instance to another for cache fusion. The physical data blocks, as well as data dictionary blocks, are shared across this interconnect.

Q6. Which files must reside on shared storage in the RAC environment?

Spfiles, Control Files, Data Files, and Redolog files should be created on shared storage.

Q7. Where does the Clusterware write when there is a network or Storage missed heartbeat?

The network ping failure is written in $CRS_HOME/log

Q8. How do you find out what OCR backups are available?

The “ocrconfig -showbackup” can be run to find out the automatic and manually run backups.

Q9. If your OCR is corrupted what options do have to resolve this?

You can use either the logical or the physical OCR backup copy to restore the Repository.

Q10. What is the difference between a single instance environment and a RAC environment?

Single InstanceRAC Environment
The instance has its own SGA (System Global Area)Each instance has its own SGA
Datafiles and control files are accessed by only one instanceDatafiles and control files shared by all  instances
Online redo logfile dedicated for read/write to only one instanceOnline redo logfile only one instance can write, but other instances can read during recovery and archiving.
Flash recovery log accessed by only one instanceFlash recovery log shared by all instances
Alert log and trace files dedicated to the instanceAlert log and trace files are private to each instance. Other instances never write or read to those files

Top class oracle rac interview questions

The below oracle RAC interview questions is helpful for your career growth.

Q11. What happens if you keep split-brain syndrome in RAC unresolved? How it can be resolved?

If you keep split-brain syndrome unresolved, then there would be a data integrity issue. The blocks changed in one instance will not be locked and could be over-written by another instance. It is resolved by using the voting disk, it will decide which node(s) will survive and which node(s) will be evicted.

Q12. Mention what is OLR?

ORL stands for Oracle Local Repository (OLR). It consists of information that enables the cluster programs to initiate with the OCR in the ASM Storage. Until the grid process is started, the ASM file is unavailable. In such a case, a local copy of the data of the OCR is required, which is stored in OLR.

Q13. What is a virtual IP address or VIP?

A virtual IP address or VIP is an alternate IP address that the client connections use instead of the standard public IP address. To configure the VIP 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.

Q14. What is an OLR?

OLR or popularly known as Oracle Local Repository consists of details related to cluster and the processes related to it when the OCR is in the ASM system. The grid process takes time to start and in the meanwhile ASM system will also be unavailable and therefore an OCR local copy is booted which is eventually stored inside OLR.

Q15. What do you understand by a rolling upgrade?

A rolling patch refers to the cluster binaries being applied on the up and running databases of the RAC environment. The cluster nodes are rolled one after another where the patched node is unavailable whereas all other instances are in the open state.

Q16. What is the ASM Metadata backup technique?

Md_backup” is the command which can be used to take ASM meta-data backup. It is also used to restore the disk group-based configurations if a storage loss for the ASM disk group is encountered.

Q17. How do we know which database instances are part of a RAC cluster?

You can query the “V$ACTIVE_INSTANCES” view to determine the member instances of the RAC cluster.

Q18. What is the default memory allocation for ASM?

Listed below:

  • In 10g the default SGA size is 1G
  • In 11g it is set to 256M and,
  • In 12c ASM it is set back to 1G.

Q19. How do you backup ASM Metadata?

You can use “md_backup” to restore the ASM diskgroup configuration in case of ASM diskgroup storage loss.

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Q20. What are the file storage options provided by Oracle Database for Oracle RAC?

RAC storage options are listed below:

  • Automatic Storage Management (ASM)
  • OCFS2 and Oracle Cluster File System (OCFS)
  • A network file system
  • Raw devices

Q21. What command would you use to check the availability of the RAC system?

The command is crs_stat -t -v (-t -v are optional)

Q22. RAC background processes?

RAC processes are LMON, LMDx, LMSn, LKCx, and DIAG.

Q23. Is it possible to use ASM for the OCR and voting disk?

No, the OCR and voting disk must be on raw or CFS (cluster file system).

Q24. Can I change the name of my cluster after I have created it when I am using Oracle Clusterware?

No, you must properly uninstall Oracle Clusterware and then re-install.

Q25. Can you have many database versions in the same RAC?

Yes, but the Clusterware version must be greater than the greater database version.

Q26. What RAC component is used for communication between instances?

Private Interconnect.

Q27.  What is the difference between normal views and RAC views?

A RAC view has the prefix ‘G’. For example, GV$SESSION instead of V$SESSION.

Q28. Which command will we use to manage (stop, start) RAC services in command-line mode?


Q29. why did we require to maintain the odd number of voting disks?

The odd number of the disk is to avoid split-brain, When Nodes in cluster can’t talk to each other they run to lock the Voting disk and whoever locks the more disk will survive, if the disk number is even there are chances that the node might lock 50% of the disk (2 out of 4) then how to decide which node to evict.

whereas when the number is odd, one will be higher than the other and each for the cluster to evict the node with less number.

Q30. How do you check the services in RAC Node?

We can check the service in the RAC node using “srvctl start service -d orcl -s RAC”

Q31. If there is some issue with virtual IP how will you troubleshoot it? How will you change virtual IP?

 srvctl modify nodeapps -A new_address

Q32. Mention what are the key characteristics of RAC or why to use RAC?

The key characteristics of RAC are:

  • Reliability: Eliminates the database server from a single point of failure. If an instance fails, the remaining instances in the cluster remain active and open.
  • Error Detection: Provides fast detection of problems in the environment. It automatically recovers from failures even before user’s notice that a failure has occurred.
  • Recoverability: Easy to recover from various types of failures.
  • Continuous Operations: provides continuous service for both unplanned and planned outages.

Q33. Why should we have separate homes for ASM instances?

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.



In the above article, we have read the top Oracle RAC interview questions. The interviewer would be possibly looking at your in-depth level of expertise and the number of hands-on you have on this particular tool. Before you arrive for your day, it is always better to brush up on your skills a bit. Please do let us know how much you liked it and keep following our blog.

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