When you design a decision support system, you must ensure that queries on large amounts of data can be performed within a reasonable time frame. Decision makers often need reports on a daily basis, so you may need to guarantee that the report can complete overnight. The key to performance in a decision support system is properly tuned queries and proper use of indexes, clusters, and hashing. By dividing the work necessary to process a statement among multiple server processes, the Oracle Server can process the statement more quickly than if only a single server process processed it. Figure  5-3 illustrates the parallel query feature of the Oracle Server.
Parallel query helps systems scale in performance when adding hardware resources.
If your system's CPUs and disk controllers are already heavily loaded, you need to alleviate the system's load before using the parallel query to improve performance. Server Concepts provides more information about parallel query processing. Many applications rely on several configurations and Oracle options. You must decide what type of activity your application performs and determine which features are best suited for it. One typical multi-purpose configuration is a combination of OLTP and decision support systems.