Components of RAC

 1. Cluster Nodes (Servers)

• Multiple physical or virtual servers (nodes) work together as a cluster.

• Each node runs its own Oracle Instance (SGA + background processes).

• All nodes access the same database files.

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2. Shared Storage

• All RAC nodes must see the same storage.

• Contains:

  • Datafiles

  • Control files

  • Redo log files

  • Archive logs

• Usually implemented using SAN / NAS / ASM (Automatic Storage Management).

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3. Cluster Interconnect (Private Network)

• High-speed private network between all nodes.

• Used for:

  • Cache Fusion (transferring data blocks between instances)

  • Global resource coordination

• Requires low-latency and high-bandwidth network (typically 10/25/40GbE or Infiniband).

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4. Oracle Clusterware

• Provides cluster management and node membership.

• Ensures only active nodes access the shared storage.

• Manages:

  • Node heartbeat monitoring

  • Automatic failover

  • VIP (Virtual IP) configuration

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5. Global Cache Service (GCS) & Global Enqueue Service (GES)

• Ensure data consistency across instances.

• Cache Fusion: If a block is modified on one node, other nodes get the updated version via interconnect (not disk I/O).

• GES manages locks, GCS manages cache coherency.

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6. Oracle RAC Database

• One database (shared) accessed by multiple instances.

• Appears as a single database to applications.

• Supports load balancing and failover through services.

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📊 RAC Architecture Diagram

          +-------------+           +-------------+
          |   Node 1    |           |   Node 2    |
          |-------------|           |-------------|
          | Oracle Inst |           | Oracle Inst |
          |   SGA/Proc  |           |   SGA/Proc  |
          +------|------+           +------|------+
                 |                         |
        ======= Private Interconnect =======
                 |                         |
          +---------------------------------------+
          |         Shared Storage (ASM)          |
          |  Control/Data/Redo/Archive Files       |
          +---------------------------------------+

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⚙ Benefits of RAC

• High Availability: Survives node failure automatically.

• Scalability: Add more nodes to increase capacity.

• Load Balancing: Workload distributed among nodes.

• Fault Tolerance: Shared database remains available if a node fails.