Read concern, write concern, causal consistency� MongoDB's consistency options are spectacularly flexible, but how on earth do you decide which to use? We will take a deep dive into the consistency levels MongoDB offers, what they mean, when to use them, and what their latency costs are. We'll explore use cases for each, and how to get the best performance out of MongoDB without having to sacrifice the developer productivity and safety these consistency levels provide. This tunability is unique to MongoDB and was the subject of a research paper published in VLDB � one of the premier academic database conferences. Judah Schvimer is a Lead Engineer on MongoDB's Replication Team. He has been an implementer and supervisor on the introduction of a number of MongoDB's consistency levels.