HashBuildAllocate
Waiting for an elected Parallel Hash participant to allocate the initial hash table.
Additional Information​
In parallel hash queries, a number of hash tables are used. This wait is seen while waiting for an elected parallel hash participant to allocate the initial hash table.
How to reduce this wait​
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.
Additional Links​
PostgreSQL documentation - Parallel Query
PostgreSQL documentation - The Statistics Collector
EDB - Parallel Hash Joins in PostgreSQL Explained
Search online​
If this article doesn't have the information you need you can try searching online. Remember, you can contribute suggestions to this page.