Use SKIP LOCKED for Non-Blocking Queue Processing#
When multiple workers process a queue, SKIP LOCKED allows workers to process different rows without waiting.
Incorrect (workers block each other):
-- Worker 1 and Worker 2 both try to get next job
begin;
select * from jobs where status = 'pending' order by created_at limit 1 for update;
-- Worker 2 waits for Worker 1's lock to release!
Correct (SKIP LOCKED for parallel processing):
-- Each worker skips locked rows and gets the next available
begin;
select * from jobs
where status = 'pending'
order by created_at
limit 1
for update skip locked;
-- Worker 1 gets job 1, Worker 2 gets job 2 (no waiting)
update jobs set status = 'processing' where id = $1;
commit;
Complete queue pattern:
-- Atomic claim-and-update in one statement
update jobs
set status = 'processing', worker_id = $1, started_at = now()
where id = (
select id from jobs
where status = 'pending'
order by created_at
limit 1
for update skip locked
)
returning *;
Reference: SELECT FOR UPDATE SKIP LOCKED