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Spotlight on Oracle 10.4 - Release Notes

Oracle RAC Architecture Overview

Oracle's Real Application Clusters (RAC) architecture harnesses the processing power of multiple interconnected computers (nodes) to access a shared Oracle database. It does so via the following components:

  • A cluster of Oracle instances on the multiple nodes.
  • A high-speed, high bandwidth communication facility known as a cluster interconnect that connects those nodes.
  • A process known as cache fusion, which allows the Oracle instances in the cluster to share database blocks between cache areas.

The following diagram, adapted from Oracle Real Application Clusters by Murali Vallath [Elsevier Digital Press, 2004] illustrates some of the basic components of an Oracle RAC cluster.

Other terms displayed in the diagram include:



IPC (Interprocess Communication Protocol)

Oracle RAC uses IPC to coordinate concurrent processes, enabling the cluster to handle many user requests at the same time.

Cluster Manager

The cluster manager provides cluster integrity by using the interconnect to process heartbeat messages between nodes.

Communication Layer

The communication layer manages communication between nodes in the cluster.

Heartbeat and Membership

The heartbeat messaging system determines which nodes are currently members of the cluster.


Listener processes establish communication paths between the database instances in a cluster.


Various monitor processes verify listener and instance processes.

Shared Disk Driver

To improve performance and availability, database files in Oracle RAC systems must be stored on multiple disks that are shared by all the nodes in the cluster, and all nodes must be able read and write to those disks. The shared disk driver on each node provides this access to all the disks in a shared disk subsystem.

Oracle RAC is ideal for data warehouse applications. More generally, large enterprises use Oracle RAC for databases where the following factors are important.

  • High availability. Oracle RAC can quickly re-distribute and balance the workload between available database instances without interrupting processing when one or more instances fail.
  • Scalability. Oracle allows you to add to or replace nodes in a cluster without reconfiguring the installation.
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