If you've ever had inconsistent data show up in your app even though you wrapped the relevant code in a transaction, you're not alone! Database isolation levels might be the solution... This talk will discuss what database isolation levels are, how to set them in Rails applications, and Rails-specific situations where not choosing the right isolation level can lead to faulty behavior. We'll also talk about how testing code that sets isolation levels requires special care and what to expect to see when monitoring your apps.