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Speed up pruning of user_ips table (matrix-org#16667)
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Silly query planner
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erikjohnston authored Nov 29, 2023
1 parent 6f2be77 commit df36696
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1 change: 1 addition & 0 deletions changelog.d/16667.misc
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Reduce database load of pruning old `user_ips`.
17 changes: 7 additions & 10 deletions synapse/storage/databases/main/client_ips.py
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Expand Up @@ -465,18 +465,15 @@ async def _prune_old_user_ips(self) -> None:
#
# This works by finding the max last_seen that is less than the given
# time, but has no more than N rows before it, deleting all rows with
# a lesser last_seen time. (We COALESCE so that the sub-SELECT always
# returns exactly one row).
# a lesser last_seen time. (We use an `IN` clause to force postgres to
# use the index, otherwise it tends to do a seq scan).
sql = """
DELETE FROM user_ips
WHERE last_seen <= (
SELECT COALESCE(MAX(last_seen), -1)
FROM (
SELECT last_seen FROM user_ips
WHERE last_seen <= ?
ORDER BY last_seen ASC
LIMIT 5000
) AS u
WHERE last_seen IN (
SELECT last_seen FROM user_ips
WHERE last_seen <= ?
ORDER BY last_seen ASC
LIMIT 5000
)
"""

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