oracle.RAC

Oracle Real Application Clusters allow multiple instances to execute against the same database. The typical installation involves a cluster of servers with access to the same disks. The nodes that actually run instances form a proper subset of the cluster. A node is defined as the collection of processors, shared memory and disks that runs an instance. A node may have more than one CPU, in either an SMP or a NUMA configuration. The node monitor is part of the vendor-provided cluster management software (CMS) that monitors the health of processes running in the cluster, and is used by CGS to control the membership of instances in Real Application Clusters.

Benefits

By using multiple instances running on their own nodes against the same database, Real Application Clusters provide the following advantages over single instance databases:

• Applications have higher availability because they can be accessed from any instance: an instance failure on one node does not prevent work from continuing on one or more surviving instances.
• More database users can be supported when a single node reaches its capacity to support additional sessions.
• Some processing, particularly operations that can be executed with parallel components, is completed faster when the work is spread across multiple nodes.
• Work can scale (more work can be completed in the same amount of time) when each instance can be optimized to support a maximum workload.