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Short Description

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

Additional Information

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

How to reduce this wait

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.

PostgreSQL documentation - How Parallel Query Works

PostgreSQL documentation - The Statistics Collector

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