You get the call at three in the morning: "The application is throwing 500 errors. We think the database is down." What do you do? Database problems can come in a nearly-infinite range of types. We don't have infinite time, but we can talk about the most common ones, and go through a step-by-step process in how to diagnose them, repair them, and bring the system back up in record time. A careful and methodical approach is essential to not making a bad situation worse, and getting the database back on all four feet quickly. We'll cover different kinds of service unavailability, data corruption, underlying host failures, and how to react to different scenarios. Use this advice to help build your run-book of how to react to those early-morning texts.