IPC - ParallelFinish
Waiting for parallel workers to finish computing.
During parallel execution plans, tasks are allocated to a number of workers. This wait is seen while the background worker processes finish their work.
Parallel queries are excellent at scanning large amounts of data the quickly returning results. Run in isolation or in a considered manner they are a useful tool.
Do not allow concurrent parallel queries from many users to flood system CPU or IO resources.
Adjust max_worker_process , max_parallel_workers and max_parallel_workers_per_gather to control response of your query and overall impact to the system.