Minor locking tweaks to reduce contention #647
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A couple of places where a Publish was locked FOR UPDATE can safely use shared locks rather than exclusive locks: - when adding publish items, we want to lock the Publish to ensure it remains in PENDING state during our update. But we won't actually change the state of the Publish, so we only need a read/shared lock. - similarly during commit, we want to lock the Publish to ensure it's in PENDING state. In phase2 commit, we actually then update the state of the Publish, so we need an exclusive lock. In phase1 commit we don't modify the Publish and it's safe to use a read/shared lock. When using the postgresql dialect, "read=True" here maps to "FOR SHARE" which is documented at [1]. This change is meant to improve performance by eliminating some scenarios where a request would have had to wait to obtain an exclusive lock on the publish; mainly during Pulp publish of many repos, where many update and phase1 commit requests will be happening concurrently for the same publish. [1] https://www.postgresql.org/docs/current/explicit-locking.html#LOCKING-ROWS
negillett
approved these changes
Dec 12, 2023
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A couple of places where a Publish was locked FOR UPDATE can safely use shared locks rather than exclusive locks:
when adding publish items, we want to lock the Publish to ensure it remains in PENDING state during our update. But we won't actually change the state of the Publish, so we only need a read/shared lock.
similarly during commit, we want to lock the Publish to ensure it's in PENDING state. In phase2 commit, we actually then update the state of the Publish, so we need an exclusive lock. In phase1 commit we don't modify the Publish and it's safe to use a read/shared lock.
When using the postgresql dialect, "read=True" here maps to "FOR SHARE" which is documented at [1].
This change is meant to improve performance by eliminating some scenarios where a request would have had to wait to obtain an exclusive lock on the publish; mainly during Pulp publish of many repos, where many update and phase1 commit requests will be happening concurrently for the same publish.
[1] https://www.postgresql.org/docs/current/explicit-locking.html#LOCKING-ROWS