Interview Questions


Oracle RAC Interview Questions

A cluster comprises multiple interconnected computers or servers that appear as if they are one server to end users and applications. Oracle RAC enables you to cluster Oracle databases. Oracle RAC uses Oracle Clusterware for the infrastructure to bind multiple servers so they operate as a single system.



              Oracle RAC Interview Questions And Answers


Q1. What is OCLUMON used for in a cluster environment?

Ans.The Cluster Health Monitor (CHM) stores operating system metrics in the CHM repository for all nodes in a RAC cluster. It stores information on CPU, memory, process, network and other OS data, This information can later be retrieved and used to troubleshoot and identify any cluster related issues. It is a default component of the 11gr2 grid install. The data is stored in the master repository and replicated to a standby repository on a different node.

Q2. What is cache fusion?

Ans. In a RAC environment, it is the combining of data blocks, which are shipped across the interconnect from remote database caches (SGA) to the local node, in order to fulfill the requirements for a transaction (DML, Query of Data Dictionary)


Q3. What is split brain?

Ans. 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 thesame 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?

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

Q5. What is a VIP in RAC use for?

Ans. The VIP is an alternate Virtual IP address assigned to each node in a cluster. During a node failure the VIP of the failed node moves to the surviving node and relays to the application that the node has gone down. Without VIP, the application will wait for TCP timeout and then find out that the session is no longer live due to the failure.

Q6.How do we know which database instances are part of a RAC cluster?

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

Q7. What is OCLUMON used for in a cluster environment?

Ans. The Cluster Health Monitor (CHM) stores operating system metrics in the CHM repository for all nodes in a RAC cluster. It stores information on CPU, memory, process, network and other OS data, This information can later be retrieved and used to troubleshoot and identify any cluster related issues. It is a default component of the 11gr2 grid install. The data is stored in the master repository and replicated to a standby repository on a different node.

Q8. What files can be stored in the ASM diskgroup?

Ans. In 11g the following files can be stored in ASM diskgroups.

·         Datafiles

·         Redo logfiles

·         Spfiles

In 12c the files below can also new be stored in the ASM Diskgroup

Password file

Q9. What it the ASM POWER_LIMIT?

Ans. This is the parameter which controls the number of Allocation units the ASM instance will try to rebalance at any given time. In ASM versions less than the default value is 11 however it has been changed to unlimited in later versions.

Q10. What is a rolling upgrade?

Ans. A patch is considered a rolling if it is can be applied to the cluster binaries without having to shutting down the database in a RAC environment. All nodes in the cluster are patched in a rolling manner, one by one, with only the node which is being patched unavailable while all other instance open.

Q11. What are some of the RAC specific parameters?

Ans. Some of the RAC parameters are:






Q12. What is the future of the Oracle Grid?

Ans. The Grid software is becoming more and more capable of not just supporting HA for Oracle Databases but also other applications including Oracle’s applications. With 12c there are more features and functionality built-in and it is easier to deploy these pre-built solutions, available for common Oracle applications.

Q13. Mention what is split brain syndrome in RAC?

Ans.In Oracle RAC, all the instances/servers communicate with each other using a private network.  When the instance members in a RAC fail to ping/connect to each other via this private network and continue to process data block independently. Then this process is referred as Split Brain Syndrome.

Q14. What happens if you keep split brain syndrome in RAC unresolved? How it can be resolved?

Ans.If you keep split brain syndrome unresolved, then there would be 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.

Q15. Mention how can you determine what protocol is being used for Interconnect traffic?

Ans.To determine what protocol is being used for Interconnect traffic you can look at the database alert log for the time period when the database was started up.

Q16. Mention what are the tools provided in Oracle Enterprise Manager?

Ans.Tools provided in Oracle Enterprise Manager are,

Grid Control-

·         It is used to deliver the centralized management system and provides configuration and administration capabilities.

·         It provides the cost reduction plans and provides higher efficiency

Database Control-

·         It is used as a graphical management tool to manage the database to make it configure automatically.

·         It is related to the Oracle Clusterware. It is used to maintain the services of the Oracle RAC.

·         It also manages the server pools that are being created with the Oracle Clusterware and provision to manage it from a single place.

Q17. Mention what is the difference between Instance recovery and Crash recovery?

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

Q18. What if your OCR (Oracle Cluster Registry) is corrupted?

Ans.if your OCR is corrupted, you can either use the logical or physical OCR backup copy to restore the repository.

Q19. Mention what is OLR?

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

Q20. Discuss OEM tools?

AnsThere are basically two OEM tools: Database Control and Grid Control

Database control:

·         A tool used for managing graphics in such a way that the database is able to make its configurations manually

·         The server pools are also managed as a result of Oracle Clusterware. The provision is made such that it can be operated and managed from one location itself

·         The services related to Oracle RAC and Oracle Clusterware can be managed by making use of Database control tool

Grid control:

·         It is a system for delivering a centralized level of management along with administration and configuration related capabilities.

·         Higher efficiency and reduction in cost for plans are also provided by Grid control.

Q21. What is the ASM Metadata backup technique?

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

Q22. Explain the use of interconnect?

Ans. Data blocks are shipped across a private network from a single instance to a different instance by making use of cache fusion. The data dictionary and the physical blocks are also shared by making use of interconnect.

Q23. The shared storage in RAC consists of some files. Name them. Also, what would be your approach to monitor the protocol being used for interconnect traffic?


·         This is the most asked Oracle RAC Interview Questions in an interview. Control files, Spfiles, Redolog file, and DataFiles are the ones present in the shared storage.

·         Looking and monitoring the database alert log closely for the stipulated time period especially when the database was initially started up will help you determine the protocol.

Q24.What Are Oracle Kernel Components (nothing But How Does Oracle Rac Database Differs Than Normal Single Instance Database In Terms Of Binaries And Process)?


Basically Oracle kernel need to switched on with RAC On option when you convert to RAC, that is the difference as it facilitates few RAC bg process like LMON, LCK, LMD, LMS etc.

To turn on RAC:

·         # link the oracle libraries

·         $ cd $ORACLE_HOME/rdbms/lib

·         $ make -f rac_on

·         # rebuild oracle

·         $ cd $ORACLE_HOME/bin

·         $ relink oracle

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

Q25. What Is The Difference Between Crsctl And Srvctl?


·         Crsctl manages cluster ware-related operations:

·         Starting and stopping Oracle Cluster ware.

·         Enabling and disabling Oracle Cluster ware daemons.

·         Registering cluster resources.

·         Srvctl manages Oracle resource–related operations:

·         Starting and stopping database instances and services.

·         Also from 11gR2 manages the cluster resources like network, vip, disks etc.

Q26.How To Control Oracle Cluster Ware?


To start or stop Oracle Cluster ware on a specific node:

·         # crsctl stop crs

·         # crsctl start crs

To enable or disable Oracle Cluster ware on a specific node:


Akal Singh
Oracle Certified Master, 20+ yrs exp
Akal Singh stands at the forefront of the fastest moving technologies in IT Industry. He spent his past 20 years as Oracle DBA with skills into DBA Support, High Availability Design & Implementations, Technical Solutions, Automation using Scripting, Database Designing & as a Corporate Trainer too. With deep technical industry knowledge, Akal Singh has implemented many real time projects on advance Database areas.

His certification list includes many OCP, Oracle Certified Expert/Specialist (OCE) and Oracle Certified Master (OCM). He is an expertise in OS Administrations, Virtualizations/VMWare and Oracle Database 8i/9i/10g/11g & 12c, RAC, Data Guard, ASM, Oracle Exadata, Oracle Performance Tuning, Golden Gate, Streams, Oracle Security & many more advance technologies.

Akal Singh is also recognized as Senior Corporate Instructor and worked with Oracle University training division providing more than 300 corporate trainings into database advance concepts.

Certifications include :
  • Oracle Certified Professional (OCP) 9i
  • Oracle Certified Professional (OCP) 10g
  • Oracle Certified Professional (OCP) 11g
  • Oracle 10g Certified RAC Expert (OCE)
  • Oracle 11g Certified Expert (RAC) and Grid Infrastructure (OCE)
  • Oracle 10g Certified Master (OCM)
  • Oracle 11g Exadata Certified Implementation Specialist
  • Oracle Database 12c: RAC and Grid Infrastructure Administrator
  • Oracle Exadata X5 Administration
  • Oracle RAC 11g Release 2 and Grid Infrastructure Administration
  • Foundation Certificate in IT Service Management  ( ITIL Certificate ) 

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