Controlling parallel processing for queries
There are two types of parallel processing available. The first is a parallel I/O that is available at no charge. The second is DB2® Symmetric Multiprocessing, a feature that you can purchase. You can turn parallel processing on and off.
Even if parallelism is enabled for a system or job, the individual queries that run in a job might not actually use a parallel method. This decision might be because of functional restrictions, or the optimizer might choose a non-parallel method because it runs faster.
Queries processed with parallel access methods aggressively use main storage, CPU, and disk resources. The number of queries that use parallel processing must be limited and controlled.