Oracle RAC

According to the Oracle website, "the Oracle Real Application Clusters (RAC) is a cluster database with a shared cache architecture that overcomes the limitations of traditional shared-nothing and shared-disk approaches to provide highly scalable and available database solutions for all your business applications." Succinctly, this means that Oracle RAC allows a single physical Oracle database to be accessed by simultaneous instances of Oracle running across several different CPUs. Furthermore in a cluster environment, applications have access to several different servers that operate together as a single entity.

Load Balancing

One of the most notable features of Oracle RAC is referred to as load balancing. In instances when the system is experiencing a high level of activity, this functionality gives Oracle the ability to redirect traffic to another server or node in the system. This can be especially beneficial when the system is afflicted with an unexpected server crash or when the operating system or one of the hardware components fails.

There are basically two different types of load balancing that occur in Oracle RAC--server and client load balancing. In server load balancing a query optimizer is used to determine how to distribute the workload across the nodes for optimal processing; whereas in client load balancing, connection requests are appropriated across the different nodes to prevent access failure. Moreover with Oracle RAC, if a system failure does occur, the switchover to another node is virtually transparent to the user.

To summarize, Oracle RAC provides users with several advantages, which optimize the performance of their databases. In particular, the cluster architecture maximizes the resources available to the application by redirecting the load to other servers in the linked group. This significantly improves the productivity of the application by reducing idle time that results from system failure.