Akka persistence enables stateful actors to persist in their internal state so that it can be recovered when an actor is started, restarted after a JVM crash or by a supervisor, or migrated in a cluster. The key concept behind Akka persistence is that only changes to an actor’s internal state are persisted but never its current state directly (except for optional snapshots). These changes are only ever appended to storage, nothing is ever mutated, which allows for very high transaction rates and efficient replication. Stateful actors are recovered by replaying stored changes to these actors from which they can rebuild internal state. This can be either the full history of changes or starting from a snapshot which can dramatically reduce recovery times. Akka persistence also provides point-to-point communication with at-least-once message delivery semantics.

1. An overview:
Akka Persistence
Prabhat Kashyap
Sr. Software
Consultant
Knoldus Inc.

2. Agenda
●
Introduction
●
Architecture
●
Creating Akka Persistence
●
Persistence FSM
●
Persistence Query

3. Introduction
Actor
Names: Empty
Message

4. Introduction
Actor
Names: [Test]

5. Introduction
Actor
Names: [Test]
Crashed

6. Introduction
Actor
Names: Empty
Crashed

7. Introduction
Actor
Names: Empty
Crashed
Database

8. Introduction
Actor
Names: [Test]
Database

9. Introduction
Actor

10. Introduction
Message
Actor

11. Introduction
Message
Actor
Command

12. Introduction
Message
Actor
Command
Database
Event

13. Architecture
●
PersistentActor
●
AsyncWriteJournal
●
Snapshot store

14. Persistence Query
●
CQRS Pattern
●
Introduction
●
System to view Account Logs

15. CQRS Pattern

16. Queries
●
persistenceIds
●
currentPersistenceIds
●
eventsByPersistenceId
●
currentEventsByPersistenceId
●
eventsByTag
●
currentEventsByTag

17. References
●
Salma Khater’s course on learning Akka.
●
Akka Documentation.