Real Application Clusters

As you know, a single server can have one or more CPUs within it. You can also use a technique called
clustering to combine more than one server into a larger computing entity. The Oracle database has sup-
ported the ability to cluster more than one instance into an single logical database for over 15 years.
Oracle combines multiple instances into a cluster. Since Oracle9i, Oracle has called these clusters Real Application Clusters, commonly referred to as RAC.
As Figure 1-2 shows, RAC instances share a common source of data, which allows RAC to provide
greater database horsepower for scalability while also providing higher levels of availability.

One of the best features of RAC is that you, as an application developer, don’t even have to think about
it, since a RAC implementation uses the same API and SQL that a single instance uses. You also don’t
have to worry about whether your Oracle application will be deployed to a single instance or a cluster
when you are designing and creating your application, since there are virtually no specific performance
considerations that only affect a RAC installation. As a developer, you don’t really have to know anything
more about Real Application Clusters.