6 ms·
But you will have marked it as in progress by setting the "expire" to a non-zero value, preventing any other workers from trying to work on it. How will they kn
by shawnz 5y ago
But you will have marked it as in progress by setting the "expire" to a non-zero value, preventing any other workers from trying to work on it. How will they know that the worker which marked it actually crashed and will never finish?
By using SELECT ... FOR UPDATE SKIP LOCKED, the record will automatically get unlocked if the worker crashes.
- jffry 5y agoNot sure. Maybe something else is responsible for identifying "stuck" jobs and kicking them out to humans to decide what to do (assuming worker crashes are rare) If we're talking PostgreSQL specifically, and newer-ish Postgres (9.5+ I think), then you can leverage its abilities to do all this in one atomic query: UPDATE jobs SET status='working' WHERE id = (SELECT id FROM jobs WHERE status=NULL LIMIT 1 FOR UPDATE SKIP LOCKED) RETURNING id
- shawnz 5y agoIf you are willing to use SELECT ... FOR UPDATE SKIP LOCKED, then you can implement the queue without any UPDATE query or status column at all. Just lock the record to mark it as in progress, that is how you get the benefit that when the worker crashes, it will automatically be returned to the queue.
- sorokod 5y agoThis approach has its own gottchas.