Debugging Postgres: The System Tables That Actually Tell You What’s Wrong
When a migration hangs, a query slows to a crawl, or a deploy just sits there, most people reach for the same first move: kill it and try again. That works about as often as it doesn’t. Postgres already knows what’s wrong — it’s just keeping the answer in a handful of system catalogs and stats views that almost nobody looks at until things are already on fire. This is a walkthrough of the tables I actually check, in the order I check them, when something breaks — with a running example: a migration that adds a NOT NULL column and backfills it on a 20-million-row orders table, which has been “running” for 25 minutes with no sign of finishing. ...