You're woken up in the middle of the night to your phone. Your app is down and you're on call to fix it. Eventually you track it down to "something with the db," but what exactly is wrong? And of course, you're sure that nothing changed recently… Knowing what to fix, and even where to start looking, is a skill that takes a long time to develop. Especially since Postgres normally works very well for months at a time, not letting you get practice! In this talk, I'll share not only the more common failure cases and how to fix them, but also a general approach to efficiently figuring out what's wrong in the first place.