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The previous resync code in zmstats and zmaudit used multi-table
UPDATEs against Event_Summaries that joined the bucket tables:
UPDATE Event_Summaries es
LEFT JOIN (SELECT ... FROM Events_Hour ...) h ON ...
LEFT JOIN (SELECT ... FROM Events_Day ...) d ON ...
... SET es.HourEvents = h.c, ...
zmaudit additionally used scalar correlated subqueries against Events
for the Total/Archived columns and against Events for Storage.DiskSpace.
MariaDB takes S-locks on the joined and sub-queried rows for the
duration of any multi-table UPDATE statement, regardless of isolation
level. event_update_trigger and event_delete_trigger hold X-locks on
those same bucket rows while they walk the trigger body, so the resync
deadlocks against active event lifecycle traffic. Captured a textbook
example in SHOW ENGINE INNODB STATUS:
TX(1) zma: HOLDS X Events_Hour[42229643]
WAITS X Event_Summaries[28]
TX(2) zmstats: HOLDS X Event_Summaries[2,4,5,...,28,...,73]
WAITS S Events_Hour[42229643]
Replace the JOIN/subquery pattern in both scripts with a snapshot phase
followed by per-monitor UPDATEs:
1. SELECT MonitorId, COUNT(*), SUM(DiskSpace) FROM each bucket
(and the equivalent Total/Archived aggregate from Events).
Plain SELECTs do consistent reads and take no row locks.
2. SELECT MonitorId FROM Event_Summaries to widen the universe so
monitors with empty buckets still get zeroed out.
3. For each monitor, UPDATE Event_Summaries SET ... WHERE MonitorId=?.
Each UPDATE only X-locks one ES row and reads no other table.
zmaudit's five separate UPDATEs collapse to one snapshot phase plus
one UPDATE per monitor. Storage DiskSpace gets the same treatment.
zmstats keeps the same outer transaction (BEGIN ... COMMIT, RC
isolation, retry on 1213) so the bucket DELETEs and the resync stay
atomic, but the resync no longer reads the bucket tables under lock.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>