Reverses the advisory-lock approach (7309d1d) — it treated a replica race that
wasn't the cause and added a new indefinite-hang mode (a sibling/stale migrator
holding the xact lock).
Real cause of the 0040 hang (operator-diagnosed 2026-06-07): web has always been
a single replica. The migration's ALTER series_page queued behind a concurrent
tag-merge that held a series_page lock for minutes — _do_merge repoints
series_page then runs _create_protective_aliases, an unindexed full scan of
image_record (JSON column, ~59k rows). Migrations ran with no lock_timeout, so
the DDL hung indefinitely and silently.
Fix: SET lock_timeout (default 30s, env-overridable) on the migration connection
before alembic's transaction. A blocked DDL now fails fast with 'canceling
statement due to lock timeout'; the entrypoint exits non-zero so the deploy
retries / surfaces loudly instead of wedging. General protection for every
future migration. (The slow _create_protective_aliases scan — the actual lock
holder — is the separate perf fix still under discussion.)
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
bvandeusen
8e98e79968