Akka Persistence for event sourcing

Akka Persistence is a relatively newer module within the Akka toolkit. It became available as experimental in the 2.3.x series. Throughout that series, it went through quite a few changes as the team worked on getting the API and functionality right. When Akka 2.4.2 was released, the experimental label was removed, signifying that persistence was stable and ready to be leveraged in production code.

Akka Persistence allows stateful actors to persist their internal state. It does this not by persisting the state itself, but instead as changes to that state, using a configurable Akka Persistence journal to do so. It uses an append-only model to persist these state changes, allowing you to later reconstitute the state by replaying the changes to that state. It also allows you to take periodic snapshots and use those to reestablish an actor's state as a performance optimization for long lived entities with lots of state changes.

Akka Persistence's...