What is Real Application Clusters?

Real Application Clusters (RAC) is a technology that links one or more individual computers so that they function as one system. RAC enables each computer, or node, that is a member of a cluster database to share access to the Oracle database. If one cluster node fails or is taken offline, then the other cluster nodes continue operating and the entire RAC database remains available. This means that two or more inexpensive computers appear to applications as if they were a much more powerful, and more expensive, computer.

To increase the performance of a two-node RAC database, you can add cluster nodes. Each additional node can help speed up application processing, support more users or processes, or both. In addition, you can also add cluster nodes to increase the availability and reliability of a two-node RAC database. The more nodes that your RAC environment has, the less the effect that the loss of any individual node has on the database.

Note:

You can include up to four single-processor nodes or two dual-processor nodes in an Oracle Database Standard Edition installation with RAC. You must upgrade to the Oracle Database Enterprise Edition to add additional nodes.