Tuning Global Cache

Abstract

Real Application Cluster (RAC) can be considered as an extension to the single instance configuration. As a concept, this is true, because RAC is a composition of several instances of Oracle. However, there are quite a few differences in the management of these components, the additional background process, the additional files, and the sharing of resources between instances, not to mention the additional layered components present at the operating system level to support a clustered hardware environment. All of these additional components in a RAC system make it different from a single-instance configuration. It is also in a RAC configuration that the real difference between a database and an instance is noticed. Although this difference does exist in a regular single-instance configuration, this is seldom noticed because the database and an instance are not distinguished from each other as they are in a RAC configuration (e.g., in a single-instance configuration, the instance and the database are identified by the same name).