Parallel Scans

The BM25 index supports parallel scans. You can check if the Postgres query planner chose a parallel scan by running EXPLAIN on a query. The following Postgres settings must be configured to increase the number of parallel workers.

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Max Parallel Workers

max_parallel_workers and max_worker_processes control how many workers are available to parallel scans. max_worker_processes is a global limit for the number of available workers across all connections, and max_parallel_workers specifies how many of those workers can be used for parallel scans.

These settings must be changed inside postgresql.conf, and Postgres needs to be restarted afterward.

max_worker_processes = 16;
max_parallel_workers = 16;

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Max Parallel Workers per Gather

max_parallel_workers_per_gather is a limit for the number of parallel workers that a single parallel query can use. The default is 2. This setting can be set in postgresql.conf to apply to all connections, or within a connection to apply to a single session.

SET max_parallel_workers_per_gather = 16;