PostgreSQL: debugging a slow query and optimizing it

It's Friday at 6:30 PM. Your query takes 4 seconds to respond in prod. The client sent you a screenshot of their loading screen. Your phone is ringing. There's a cold beer waiting for you. That's the context in which you're going to debug a slow PostgreSQL query. Good news: 80% of PostgreSQL performance problems have an identifiable cause in under 10 minutes with the right tools. This guide follows the logical order of a real investigation — not an exhaustive PG feature catalog, but a method tha