Fresh off the press: Transactions in Mongo! In the past, MongoDB limited the atomicity of any mutation to one document. But with 4.0, multi-document transactions are fully supported! This session will explore the transaction behavior in Mongo. We will discuss some of the underlying mechanisms enabling transactions, as well as the behavior of transactions, sessions, and read consistency guarantees. We will also discuss caveats and reasons you might not want or need transactions after all.