fix: sort zoids in CacheWarmer._flush to prevent PK-index deadlock#61
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Concurrent Waitress workers with overlapping pending sets deadlocked on cache_warm_stats PK index when their INSERT ... ON CONFLICT DO UPDATE acquired row locks in opposing orders. Set iteration order is not stable across processes, so two flushes could see the same zoids in different orders. Sort zoids before the upsert for a deterministic row-lock acquisition order. Added regression test verifying the INSERT parameter is sorted. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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Summary
INSERT ... ON CONFLICT DO UPDATEintocache_warm_statsso concurrent Waitress workers acquire PK row locks in the same order and can never deadlock.psycopg.errors.DeadlockDetectedonINSERT ... while inserting index tuple (…) in relation "cache_warm_stats"between two worker processes.zoids = list(self._pending)—setiteration order is unstable across processes, so two workers with overlapping pending sets upsert the same rows in opposing orders and deadlock on the PK index.TestCacheWarmerFlushEdgethat mocks the cursor and asserts the bigint[] bound to the INSERT is sorted. Verified the test fails onlist(...)and passes onsorted(...).Test plan
pytest tests/test_cache_warmer.py— 24/24 green locallyDeadlockDetectedfromcache_warmer._flushafter deploy🤖 Generated with Claude Code