The following parameters configure Adaptive Server for parallel query processing – where the optimizer evaluates each query to determine whether it is eligible for parallel execution.
To determine the best values to use for the configuration parameters, and to understand how these values affect the optimizer, see Chapter 2, “Optimizer Overview” and Chapter 8, “Parallel Query Optimization” in the Performance and Tuning Guide: Optimizer and Abstract Plans.
number of worker processes, max parallel degree, and max scan parallel degree control parallel query processing at the server level. Using the parallel_degree, process_limit_action, and scan_parallel_degree options to the set command can limit parallel optimization at the session level, and using the parallel keyword of the select command can limit parallel optimization of specific queries. Figure 4-6 shows the precedence of the configuration parameters and session parameters.
Figure 4-6: Precedence of parallel options
