Think you could land a DBA job at GitHub?You've just been paged. Every query is failing to execute. Find out why.Years ago at GitHub, this was a question Sam Lambert would ask in interviews.The solution involved a downed database that started with a MySQL schema change needing an exclusive lock on a table, but it couldn't get one. Another session had already touched that table and never committed. That open transaction blocked the schema change.Once the schema change was waiting, new queries on the same table queued up behind it. Nothing was deadlocked. Nothing would time out on its own. The whole pile-up sat there until someone found the connection at the top of the chain and killed it.(By the way, you'd avoid this MySQL lock on PlanetScale Vitess since ALTER would have been an online schema change, copying in the background and only taking a brief lock at cutover.)This isn't rare, and it isn't exclusive to MySQL. You can reproduce the same pile-up on Postgres just as easily.Want to see a stuck database?You won't need elevated permissions. A normal application connection is enough.All it takes is an unhandled exception and a poorly timed migration.Say you have a Postgres database with a hot table named orders.On one connection, a transaction begins a SELECT query, but the app throws an exception.-- Connection A: Ordinary application user