chore(db): reword stats-migration comment

packages/db/migrations/20260725100500_env_builds_status_group_statistics.sql

@@ -0,0 +1,35 @@
+-- +goose Up
+-- +goose NO TRANSACTION
+
+-- ANALYZE cannot run inside a transaction; bound the pass so it neither
+-- hangs unbounded nor dies to a short session default.
+SET statement_timeout = '1h';
+
+-- status_group='pending' is rare enough (well under a hundredth of a percent
+-- of the table, measured in production) that the default statistics sample
+-- statistically never catches it: 'pending' is absent from the column's MCV
+-- list, so the planner underestimates it by orders of magnitude and drives
+-- InvalidateUnstartedTemplateBuilds from the pending-scan side — tens of
+-- thousands of index probes into env_build_assignments per execution instead
+-- of one selective (env_id, tag) lookup. A larger per-column sample makes
+-- rare-but-hot status groups visible and flips the join order back.
+ALTER TABLE public.env_builds ALTER COLUMN status_group SET STATISTICS 2000;
+
+-- Rebuild the column stats immediately: autoanalyze would otherwise wait
+-- for the change threshold, leaving the misestimate live for hours.
+ANALYZE public.env_builds;
+
+-- The migrator session is reused for subsequent migrations: restore its
+-- baseline (scripts/migrator.go sets 3h per connection).
+SET statement_timeout = '3h';
+
+-- +goose Down
+-- +goose NO TRANSACTION
+
+SET statement_timeout = '1h';
+
+ALTER TABLE public.env_builds ALTER COLUMN status_group SET STATISTICS -1;
+
+ANALYZE public.env_builds;
+
+SET statement_timeout = '3h';