Re: Delete from locking ordering differences

We are wondering if anyone can explain the difference we are having in production with the following queries:

DELETE FROM store

WHERE id IN (

  SELECT id FROM store 

  FOR UPDATE SKIP LOCKED 

  ORDER BY ID

  LIMIT 1000

)

RETURNING id, payload

This query is sometimes executed with high concurrency, and then can hang indefinitely, we assume because of a locking problem that postgresql is not detecting as a deadlock.

This alternative query does not have the hanging problem:

WITH store_ids AS (

  SELECT id FROM store 

  FOR UPDATE SKIP LOCKED 

  ORDER BY ID

  LIMIT 1000

)

DELETE FROM store s

USING store_ids si 

WHERE s.id = si.id

RETURNING s.id, s.payload

Can anyone explain why the first query is expected to fail (hang), and the second query does not have this problem? We would be interested in more understanding on this. Thanks!