Oracle9i introduced an evolution of the Oracle Parallel Server (OPS) technology called Real Application Clusters. In the past, OPS had been primarily used for availability, because there were performance penalties for using OPS with OLTP and some other types of applications.
Real Application Clusters have eliminated these problems, making it possible for most applications to scale over a cluster of machines. Oracle claims that with Real Application Clusters, each new machine can add as much as 90% of the performance of the standalone machine. Even if this new technology doesn't reach these heights, you can still deploy the same application on a Real Application Cluster that you can on a single database server, with the capability of adding more nodes to the cluster, rather than upgrading your database server to increase overall throughput.
Oracle Database 10g has added cluster workload management, a feature that lets you specify how different services, or workloads, use the nodes in a cluster. Cluster workload management gives you the ability to provision the nodes in a cluster to different parts of the overall application workload.
Real Application Clusters are discussed in more detail in Chapter 8.