Interview Bite

Introduction to Oracle RAC Interview Questions

Oracle Real Application Clusters (RAC) is a high-availability database solution that allows multiple servers to access a single database simultaneously. It’s a critical technology for DBAs, architects, and infrastructure engineers working with enterprise Oracle systems.

This comprehensive guide covers:

• Oracle RAC fundamentals and architecture
• Installation and configuration
• Performance tuning
• Troubleshooting
• Latest RAC features

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Section 1: Oracle RAC Fundamentals (10 Questions)

1. What is Oracle RAC?

Oracle RAC (Real Application Clusters) is a cluster database solution where multiple instances access a single database, providing:

• High availability
• Scalability
• Load balancing
• Fault tolerance

2. What are the key components of Oracle RAC?

• Clusterware (Oracle Clusterware)
• Shared Storage (ASM, SAN, NAS)
• Interconnect (private network for node communication)
• Database Instances (multiple instances on different nodes)

3. How does RAC differ from a single-instance database?

Feature	Single Instance	RAC
Availability	Single point of failure	High availability
Scalability	Vertical only	Horizontal scaling
Performance	Limited	Load balancing
Cost	Lower	Higher

4. What is Oracle Clusterware?

Oracle Clusterware is the foundation layer that:

• Manages cluster nodes
• Provides node membership
• Handles failover
• Manages resources

5. What is the role of voting disks in RAC?

Voting disks:

• Determine cluster node membership
• Resolve split-brain scenarios
• Require odd number (typically 3)

6. What is OCR (Oracle Cluster Registry)?

OCR stores:

• Cluster configuration
• Resource profiles
• Dependency information

7. What is the interconnect in RAC?

A private, high-speed network (typically 10G+) used for:

• Cache fusion traffic
• Heartbeat communication
• Global resource directory synchronization

8. What is Cache Fusion?

Oracle’s memory-to-memory transfer mechanism that:

• Shares data blocks between instances
• Maintains cache coherency
• Reduces disk I/O

9. What are RAC services?

Logical abstractions that:

• Group workloads
• Enable load balancing
• Manage failover

10. What is SCAN (Single Client Access Name)?

A single hostname that:

• Provides connection load balancing
• Simplifies client configuration
• Resolves to multiple IPs (typically 3)

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Section 2: RAC Administration (10 Questions)

11. How do you add a node to an existing RAC cluster?

Steps:

1. Install Oracle software on new node
2. Run addnode.sh
3. Add to cluster using crsctl add node
4. Create new instance

12. What is the difference between CRSCTL and SRVCTL?

• CRSCTL – Manages clusterware
• SRVCTL – Manages database resources

13. How do you check RAC status?

crsctl check cluster
srvctl status database -d dbname

14. What is TAF (Transparent Application Failover)?

A feature that:

• Automatically reconnects sessions
• Fails over to surviving nodes
• Can resume queries

15. How do you patch a RAC environment?

1. Apply OPatch to one node
2. Roll out to other nodes
3. Use rolling or non-rolling approach

16. What is the difference between rolling and non-rolling patches?

• Rolling – Patches nodes sequentially (no downtime)
• Non-rolling – Requires complete outage

17. How do you relocate services in RAC?

srvctl relocate service -d dbname -s service_name -i instance_name -t target_instance

18. What is ACFS in RAC?

Oracle ASM Cluster File System:

• Cluster-aware filesystem
• Supports snapshots
• Used for Oracle homes, binaries

19. How do you monitor RAC performance?

Tools:

• AWR (Automatic Workload Repository)
• Cluster Health Monitor (CHM)
• Oracle Enterprise Manager

20. What is the role of GES and GCS in RAC?

• GES (Global Enqueue Service) – Manages locks
• GCS (Global Cache Service) – Manages block transfers

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People Also Ask (10 Additional Questions)

Troubleshooting RAC

21. How to troubleshoot node evictions?
    Check:

• Interconnect issues
• Voting disk problems
• Memory pressure

22. What causes “split brain” in RAC?
    When nodes can’t communicate but both think they’re active.
23. How to resolve OCR corruption?
    Use ocrconfig with backup.

Performance Tuning

24. How to optimize Cache Fusion?

• Proper interconnect setup
• Correct buffer cache sizing
• Use services for workload separation

25. What is “gc cr block busy” wait event?
    Indicates contention for consistent read blocks.

High Availability

26. How does RAC provide HA?

• Automatic failover
• Service relocation
• Instance crash recovery

27. What is FAN (Fast Application Notification)?
    Event notification system for rapid failover.

Storage

28. Why use ASM with RAC?

• Cluster-aware storage
• Automatic rebalance
• Striping and mirroring

29. What is the difference between NORMAL and HIGH redundancy?

• NORMAL – 2-way mirror
• HIGH – 3-way mirror

Latest Features

30. What’s new in Oracle RAC 19c?

• Application Continuity improvements
• Sharded database support
• Enhanced diagnostics

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Conclusion

This comprehensive Oracle RAC interview guide covers:
✔ Architecture fundamentals
✔ Administration tasks
✔ Performance tuning
✔ Troubleshooting
✔ Latest features

Next Steps:

• Practice with RAC environments
• Explore Oracle documentation
• Get hands-on with Clusterware commands