Sets upper bound for parallel execution of GROUP BY operations and for arms of a UNION.
Can be set temporary for an individual connection or for the PUBLIC group. Takes effect immediately.
This parameter sets an upper bound which limits how parallel the optimizer will permit query operators to go. This can influence the CPU usage for many query join, GROUP BY, UNION, ORDER BY, and other query operators.
Systems with more than 64 CPU cores often benefit from a larger value, up to the total number of CPU cores on the system to a maximum of 512; you can experiment to find the best value for this parameter for your system and queries.
Systems with 64 or fewer CPU cores should not need to reduce this value, unless excessive system time is seen. In that case, you can try reducing this value to determine if that adjustment can lower the CPU system time and improve query response times and overall system throughput.