Why Oracle RAC Still Shines in 2025

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TL;DR Summary

Oracle RAC continues to deliver zero-downtime clustering, linear scalability, and seamless maintenance in 2025—keeping it relevant for mission-critical workloads.

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Introduction

In today’s cloud-native era, many argue that newer distributed databases have supplanted Oracle RAC. Yet, for enterprises demanding guaranteed uptime, sub-second failover, and mature support, RAC still solves real business pains.
DBAs and architects face pressure to keep systems online 24×7—RAC’s proven clusterware, ASM integration, and rolling-patch capabilities remain indispensable.

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Architecture Overview

 


  ClientApp --> SCAN[SCAN VIP]
  SCAN --> RAC_Node1
  SCAN --> RAC_Node2
  RAC_Node1 --> ASM[ASM Diskgroup]
  RAC_Node2 --> ASM
  ASM --> Shared_Storage[(Shared Disks)]
  RAC_Node1 --> DG[Data Guard]
  RAC_Node2 --> DG

• ClientApp connects via a Single Client Access Name (SCAN) for load balancing.

• RAC_Node1/2 run independent Oracle instances accessing the same ASM-managed storage.

• ASM Diskgroup abstracts disk management and provides striping/mirroring.

• Shared Disks store datafiles, redo logs, and OCR.

• Data Guard provides disaster-recovery standby to the RAC primary.

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Deep Dive

Memory & Process Architecture

• Global Cache Service (GCS): Coordinates block transfers between nodes.

• Global Enqueue Service (GES): Manages metadata locks.

• SGA Components: Shared by all instances, including library cache and buffer cache.

Component	Default Value	Purpose
CLUSTER_DATABASE	TRUE	Enables RAC mode
CACHE_FUSION	ENABLED	Inter-node block transfer
ASM_DISKGROUPS	(DATA, FRACTEMP)	ASM diskgroup list for data and temp

Redo Transport & Coordination

• Cache Fusion: Sends “dirty” blocks over the interconnect instead of disk.

• Interconnect: Private network (1–10 Gbps) dedicated for RAC heartbeat and block transfer.

• Redo Apply: Each instance writes local redo; ASM mirrors to shared storage.

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Code & Configuration Samples

# Start the RAC database
srvctl start database -d ORCL       # Launches all instances in the cluster

# Check cluster status
crsctl check cluster               # Verifies CRS, voting disks, and OCR health

# Add a new SCAN listener
srvctl add scan_listener -l scan1 -p 1521  # Creates SCAN VIP

-- Enable Transparent Data Encryption (TDE) wallet
ADMINISTER KEY MANAGEMENT SET KEYSTORE OPEN IDENTIFIED BY "StrongPwd!";
ADMINISTER KEY MANAGEMENT CREATE KEY IDENTIFIED BY "StrongPwd!" WITH BACKUP;
-- Annotated: Opens wallet and creates TDE master key

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Performance Tuning & Best Practices

1. Statistics Management: Automate DBMS_STATS.GATHER_DATABASE_STATS() weekly.

2. Interconnect Tuning: Use jumbo frames (MTU 9000) on the private network.

3. Adaptive Features: Enable MEMORY_TARGET with MEMORY_MAX_TARGET.

4. Instance Caging: Limit CPU per instance for balanced workload.

5. ASM Rebalance: Schedule low-priority rebalance to avoid IO spikes.

 

Parameter	Impact	Suggested Value
CLUSTER_INTERCONNECTS	Defines interconnect NICs	eth1,eth2
DB_CACHE_SIZE	Buffer cache per instance	25% total SGA
PGA_AGGREGATE_TARGET	Controls private memory for SQL	20% of SGA

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Security Considerations

• Network ACLs:

  BEGIN
    DBMS_NETWORK_ACL_ADMIN.CREATE_ACL(
      acl         => 'rac_acl.xml',
      description => 'RAC network rules',
      principal   => 'RAC_USER',
      is_grant    => TRUE,
      privilege   => 'connect'
    );
  END;
  

• sqlnet.ora snippet:

  SQLNET.ENCRYPTION_SERVER = required
  SQLNET.ENCRYPTION_TYPES_SERVER = (AES256)
  

• Role Separation: Grant only SYSDBA on one node; use OPERATOR for maintenance scripts.

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Real-World Case Study

Scenario: A global retailer migrated its 24×7 e-commerce platform to Oracle RAC on Exadata Cloud.

• Challenge: Single-instance DB caused 2–3 min outages per month during patching.

• Solution: Deployed 4-node RAC with rolling patching and ASM redundancy.

• Outcome: Achieved 99.999% availability, reduced patch-window to zero downtime, and saw a 30% improvement in average transaction throughput.

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Common Pitfalls & Troubleshooting

1. ORA-16837: Host crashed

   • Diagnostics:

     crsctl check cluster -all
     

   • Fix: Verify underlying OS heartbeat, increase CRSCTL set cluster property -name 'auto_recovery' -value 'true'.

2. Cache Fusion Latency

   • Diagnostics:

     SELECT * FROM GV$GES_STATISTICS;
     

   • Fix: Optimize interconnect NIC teaming or switch to InfiniBand.

3. ASM Rebalance Slowness

   • Diagnostics:

     SELECT * FROM V$ASM_OPERATION;
     

   • Fix: Set ASM_POWER_LIMIT higher during off-peak hours.

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FAQs

Q1: Is RAC overkill for small DBs?
A: If you need high availability and your SLAs demand zero downtime, RAC scales down—consider two-node deployments.

Q2: Can I run RAC on public cloud?
A: Yes—OCI, AWS, and Azure all support Oracle RAC, though network and storage configs vary.

Q3: How does RAC compare to Kubernetes-based DBs?
A: RAC offers deeper integration with ASM, rolling patches, and Oracle support—K8s DBs are emerging but less mature.

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Conclusion & Call-to-Action

Oracle RAC remains a battle-tested solution in 2025, delivering unmatched uptime, linear scalability, and mature tooling. If uptime is non-negotiable for your enterprise, RAC deserves a spot in your architecture.
Share your RAC experiences below or contact us for an in-depth workshop!

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References

1. Oracle RAC Concepts Guide – https://docs.oracle.com/en/database/oracle/oracle-database/19/radbi/index.html

2. ASM Administrator’s Guide – https://docs.oracle.com/en/database/oracle/oracle-database/19/asmag/index.html

3. Oracle Real Application Clusters Best Practices – Oracle White Paper

4. Data Guard Overview – https://docs.oracle.com/en/database/oracle/oracle-database/19/dgbkr/index.html

5. Managing Database Security – Oracle Database Security Guide