legal-halacha-drain crashed 29× with asyncpg DeadlockDetectedError. Root cause:
every short-lived cron drain re-runs the idempotent schema migrations on startup
(get_pool → _run_schema_migrations), and three jobs (metadata-drain, halacha-drain,
halacha-supervisor) all fired on the same minute (*/15 / top-of-hour). Two
processes running the DDL concurrently took AccessExclusiveLock in opposite order
→ Postgres killed one with a deadlock.
Two-layer fix:
- Root cause: wrap _run_schema_migrations in a session-level pg_advisory_lock so
only one process applies DDL at a time; concurrent migrators wait instead of
deadlocking. DDL body extracted to _apply_schema_ddl. Idempotent, schema
unchanged.
- Defence-in-depth: give each cron drain a distinct firing minute —
metadata :00, supervisor :05, halacha-drain :10, digest :12, court-fetch :17 —
so siblings no longer start at the same instant. SCRIPTS.md updated to match.
Invariants: G1 (fix at source — the single migration path — not the symptom);
G2 (no parallel control path introduced).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Chaim
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