Oracle RAC DBA Interview Questions

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  • User AvatarAshiwini
  • 30 Jan, 2025
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Oracle RAC DBA Interview Questions

  1. What is Oracle RAC?

    Oracle RAC (Real Application Clusters) is a database clustering solution that allows multiple instances to access a single database simultaneously, providing high availability, scalability, and load balancing.

  2. What are the key benefits of using Oracle RAC?

    High Availability: Ensures database availability in case of node failures.
    Scalability: Allows adding more nodes to handle increased workload.
    Load Balancing: Distributes user connections across multiple nodes for better performance.
    Failover Support: In case one node fails, the workload is transferred to another node.

  3. What are the components of an Oracle RAC architecture?

    Cluster Nodes: Physical or virtual servers running Oracle RAC instances.
    Shared Storage: Storage that all RAC nodes access (e.g., ASM, SAN, NAS).
    Oracle Clusterware: Manages cluster resources and node communication.
    Private Interconnect: High-speed network for RAC instances to communicate.
    Voting Disk: Stores information about node membership in the cluster.
    OCR (Oracle Cluster Registry): Stores cluster configuration details.

  4. What is Oracle Clusterware?

    Oracle Clusterware is Oracle’s cluster management software that coordinates RAC instances, provides high availability, and ensures communication between nodes.

  5. What is the role of SCAN (Single Client Access Name) in RAC?

    SCAN provides a single access point for client connections to the RAC database, simplifying connection management and load balancing.

  6. What is the importance of a Private Interconnect in RAC?

    The private interconnect is used for internode communication, cache fusion, and data synchronization. A high-speed, low-latency network is required to prevent performance bottlenecks.

  7. What is Cache Fusion in Oracle RAC?

    Cache Fusion is Oracle RAC’s mechanism to share data between instances via private interconnect, ensuring consistency across nodes without disk I/O.

  8. What is the function of Voting Disk in Oracle RAC?

    The Voting Disk helps in cluster membership decisions, ensuring that only the healthy nodes remain in the cluster and avoiding split-brain scenarios.

  9. What happens if a node fails in an Oracle RAC environment?

    The failed node is evicted from the cluster.
    Oracle Clusterware redistributes connections to other available nodes.
    Instance recovery is performed by the surviving nodes.

  10. How does Load Balancing work in Oracle RAC?

    Oracle RAC provides two types of load balancing:
    Client-side Load Balancing: Clients distribute connections across nodes based on SCAN.
    Server-side Load Balancing: The database directs connections based on workload and performance metrics.

  11. What is Transparent Application Failover (TAF) in Oracle RAC?

    TAF enables a client session to automatically reconnect to another node in case of a failure, ensuring minimal disruption.

  12. What is a Service in Oracle RAC?

    A service in Oracle RAC is a logical database connection point that allows workload management and high availability for applications.

  13. What is Dynamic Resource Manager (DRM) in Oracle RAC?

    DRM dynamically moves resources such as buffer cache between instances to optimize performance based on workload.

  14. What is a Voting Disk in Oracle RAC?

    A voting disk is a shared disk used to determine which nodes in the cluster are active and to prevent split-brain scenarios.

  15. What is an OCR (Oracle Cluster Registry)?

    OCR is a repository that stores cluster configuration details, including node membership, voting disk information, and resource profiles.

  16. What is a Private Interconnect in Oracle RAC?

    A private interconnect is a dedicated, high-speed network used for communication between RAC instances.

  17. What is SCAN (Single Client Access Name) in Oracle RAC?

    SCAN provides a single access point for database connections in RAC. It simplifies connection management and supports automatic failover and load balancing.

  18. What are the types of services in Oracle RAC?

    Database Service: Logical representation of a workload to distribute connections.
    VIP (Virtual IP) Service: Provides failover support for client connections.

  19. What is a Virtual IP (VIP) in Oracle RAC?

    A VIP is an IP address that is assigned to a RAC node and fails over to another node if the original node goes down, ensuring uninterrupted client connections.

  20. What is Transparent Application Failover (TAF)?

    TAF allows a client session to reconnect to another RAC instance automatically if the original connection fails.

  21. 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.

  22. 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.

  23. Explain the use of interconnect?

    It is a private network that 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.

  24. How do you determine what protocol is being used for Interconnect traffic?

    One of the ways is to look at the database alert log for the time period when the database was started.

  25. What methods are available to keep the time synchronized on all nodes in the cluster?

    Either the Network Time Protocol(NTP) can be configured or in 11gr2, Cluster Time Synchronization Service (CTSS) can be used.

  26. What file components in RAC must reside on shared storage?

    Spfiles, ControlFiles, Datafiles, and Redolog files should be created on shared storage.

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

    The network ping failure is written in $CRS_HOME/log

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

    The OCR config – shows backup can be run to find out the automatic and manually run backups.

  29. 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.

  30. How do you find out what object has its blocks being shipped across the instance the most?

    You can use the dba_hist_seg_stats.

  31. 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.

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

    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.

  33. What would be the possible performance impact in a cluster if a less powerful node (e.g. slower CPUs) is added to the cluster?

    All processing will show down to the CPU speed of the slowest server.

  34. What is the default memory allocation for ASM?

    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.

  35. How do you back up ASM Metadata?

    You can use md_backup to restore the ASM disk group configuration in case of ASM disk group storage loss.

  36. What files can be stored in the ASM disk group?

    In 11g the following files can be stored in ASM disk groups.

    • Datafiles
    • Redo logfiles
    • Spfiles

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

    • Password file