Oracle introduced Real Application Clusters (RAC) with Oracle 9i, and RAC continues to be a key feature for the current generation of databases. Oracle RAC allows a single physical Oracle database to be accessed by concurrent instances of Oracle running across several different CPUs.
An Oracle RAC is composed of a group of independent servers, or nodes, that cooperate as a single system. A cluster architecture such as this provides applications access to more computing power when needed, while allowing computing resources to be used for other applications when database resources are not as heavily required. For example, in the event of a sudden increase in network traffic, an Oracle RAC can distribute the load over many nodes, a feature referred to as server load balancing. Oracle RAC features are available to you simply by connecting to an Oracle RAC system with your Oracle driver. There is no additional configuration required.
Connection failover and client load balancing can be used in conjunction with an Oracle RAC system, but they are not specifically part of Oracle RAC.
