Why does my query drop from 3ms to 4 seconds on Tuesday with no deploy?

PostgreSQL's query planner re-evaluates execution plans whenever table statistics change, which happens asynchronously through autovacuum and ANALYZE, independent of any code deployment. A batch import, a routine vacuum after deletion, or a gradual shift in data distribution can flip an index scan to a sequential scan overnight, turning a 3ms query into a 4-second one with no error emitted and no deployment in the history. These regressions are invisible in CI because they are driven by statistics state, not code state, and no standard test harness captures plans across different statistics snapshots. Pganalyze and similar tools detect plan flips after they occur in production, but there is no upstream gate that tests query plan stability before a schema change or data migration ships. PostgreSQL proposed the pg_plan_advice contrib module in October 2025 to let operators hint or pin plan