IPC - ExecuteGather

Waiting for activity from a child process while executing a Gather plan node.

Gather waits are seen in parallel query plans where the leader is merging data from background worker processes. The planner will use at most the max_parallel_workers_per_gather for the query and the total number of workers available on the system is controlled by max_worker_processes and max_parallel_workers

Check that the total parallelism use in all queries does not saturate the CPUs available.

Check that the I/O load caused by the parallel queries can be sustained by the system.