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.tip

· one of the small things

FOR UPDATE SKIP LOCKED is the whole queue

A job queue in Postgres needs one query. Workers select pending rows FOR UPDATE SKIP LOCKED, so a row another worker holds gets skipped instead of waited on. There are no advisory locks, no polling table and no second system.

SELECT id, payload FROM jobs
WHERE status = 'pending' AND run_at <= now()
ORDER BY id LIMIT 50
FOR UPDATE SKIP LOCKED;

Run the workers at READ COMMITTED. Under REPEATABLE READ they spend all their time retrying serialization failures.

postgresqlqueues