TL;DR: Everything works great until it doesn't. I've watched dashboards look perfectly healthy — p50 latency under 50ms, error rate flat — right up until a table crosses 500k rows and suddenly specific endpoints start timing out. 📖 Reading time: ~45 min What's in this article The Moment You Know You Have a Query Problem Step 1: Enable the Tools You Actually Need Start with pg_stat_statements — Everything Else Is Guesswork Step 2: Read EXPLAIN ANALYZE Without Guessing The Index Mistakes I See Most Often N+1 Queries: The Silent Killer in ORM-Heavy Apps VACUUM, ANALYZE, and Table Bloat — The Stuff Nobody Talks About The Autovacuum Lie (And How to Stop Falling For It) The Moment You Know You Have a Query Problem Everything works great until it doesn't. I've watched dashboards look perfectly healthy — p50 latency under 50ms, error rate flat — right up until a table crosses 500k rows and suddenly specific endpoints start timing out. The failure mode is never gradual.…