The generation of parallel query plans is controlled by several configuration parameters, as well as a session level SET statement. The opf_pq_dop parameter defines the degree of parallelism or maximum number of exchange nodes that can be compiled into a query plan. A value of 0 or 1 prevents the generation of parallel plans, but any other positive value enables them. The session level set parallel <n> statement can be used to override the CBF parameter, where <n> is the degree of parallelism for queries compiled in the session.

The opf_pq_threshold parameter is a companion to opf_pq_dop and defines the cost threshold of a query plan before exchange nodes are inserted into it. Because there are slight overheads in initiating parallel query plans, compile only plans that benefit from parallel processing. The query optimizer currently compiles a serial query plan as it always has. If the degree of parallelism is defined to permit exchange nodes to be added to the plan, the cost estimate of the serial plan must still exceed the threshold value before a parallel plan is generated. The cost estimate is computed as the sum of the C and D numbers at the top of the query plan.