Lock Skip Locked

title: Use SKIP LOCKED for Non-Blocking Queue Processing impact: MEDIUM-HIGH impactDescription: 10x throughput for worker queues tags: skip-locked, queue, workers, concurrency

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