Akka persistence == event sourcing in 30 minutes
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Akka 2.3 introduces akka-persistence, a wonderful way of implementing event-sourced applications. Let's give it a shot and see how DDD and Akka are a match made in heaven :-)
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Akka persistence == event sourcing in 30 minutes
- 1. Akka persistence (message sourcing in 30 minutes) Konrad 'ktoso' Malawski Scalar 2014 @ Warsaw, PL
- 2. Konrad `@ktosopl` Malawski typesafe.com geecon.org Java.pl / KrakowScala.pl sckrk.com / meetup.com/Paper-Cup @ London GDGKrakow.pl meetup.com/Lambda-Lounge-Krakow
- 3. Konrad `@ktosopl` Malawski typesafe.com geecon.org Java.pl / KrakowScala.pl sckrk.com / meetup.com/Paper-Cup @ London GDGKrakow.pl meetup.com/Lambda-Lounge-Krakow
- 4. Konrad `@ktosopl` Malawski typesafe.com geecon.org Java.pl / KrakowScala.pl sckrk.com / meetup.com/Paper-Cup @ London GDGKrakow.pl meetup.com/Lambda-Lounge-Krakow
- 5. Konrad `@ktosopl` Malawski typesafe.com geecon.org Java.pl / KrakowScala.pl sckrk.com / meetup.com/Paper-Cup @ London GDGKrakow.pl meetup.com/Lambda-Lounge-Krakow
- 6. Konrad `@ktosopl` Malawski typesafe.com geecon.org Java.pl / KrakowScala.pl sckrk.com / meetup.com/Paper-Cup @ London GDGKrakow.pl meetup.com/Lambda-Lounge-Krakow
- 7. Konrad `@ktosopl` Malawski typesafe.com geecon.org Java.pl / KrakowScala.pl sckrk.com / meetup.com/Paper-Cup @ London GDGKrakow.pl meetup.com/Lambda-Lounge-Krakow hAkker @
- 8. mainly by Martin Krasser ! ! (as contractor for Typesafe) ! inspired by: akka-persistence https://github.com/krasserm https://github.com/eligosource/eventsourced
- 9. dependencies libraryDependencies ++= Seq(! "com.typesafe.akka" %% “akka-actor" % "2.3.0",! "com.typesafe.akka" %% "akka-persistence-experimental" % "2.3.0"! )
- 10. Show of hands!
- 11. Show of hands!
- 12. Show of hands!
- 13. Show of hands!
- 14. sourcing styles Command Sourcing Event Sourcing msg: DoThing msg persisted before receive imperative, “do the thing” business logic change, can be reflected in reaction Processor
- 15. sourcing styles Command Sourcing Event Sourcing msg: DoThing msg: ThingDone msg persisted before receive commands converted to events, must be manually persisted imperative, “do the thing” past tense, “happened” business logic change, can be reflected in reaction business logic change, won’t change previous events Processor EventsourcedProcessor
- 16. Plain Actors
- 18. count: 0 ! ! Actor An Actor that keeps count of messages it processed
- 19. count: 0 ! ! Actor An Actor that keeps count of messages it processed
- 20. count: 0 ! ! Actor An Actor that keeps count of messages it processed Let’s send 2 messages to it
- 21. count: 0 ! ! Actor An Actor that keeps count of messages it processed Let’s send 2 messages to it (it’s “commands”)
- 22. Actor ! ! class Counter extends Actor {! var count = 0! def receive = {! case _ => count += 1! }! }
- 27. Actor crash!
- 28. Actor restart
- 33. count: 1 ! ! wrong! expected count == 2! Actor restarted
- 34. Processor
- 35. var count = 0 ! def processorId = “a” ! Journal (DB) ! ! ! Processor
- 36. Journal (DB) ! ! ! Processor var count = 0 ! def processorId = “a” !
- 37. Journal (DB) ! ! ! Processor var count = 0 ! def processorId = “a” !
- 38. Journal (DB) ! ! ! Processor var count = 0 ! def processorId = “a” !
- 39. Journal (DB) ! ! ! Processor var count = 1 ! def processorId = “a” !
- 40. Journal (DB) ! ! ! Processor var count = 1 ! def processorId = “a” !
- 41. Journal (DB) ! ! ! Processor var count = 1 ! def processorId = “a” ! crash!
- 44. Journal (DB) ! ! ! Processor var count = 0 ! def processorId = “a” ! restart
- 45. Journal (DB) ! ! ! Processor var count = 0 ! def processorId = “a” ! replay! restart
- 46. Journal (DB) ! ! ! Processor var count = 0 ! def processorId = “a” !
- 47. Journal (DB) ! ! ! Processor var count = 0 ! def processorId = “a” ! replay!
- 48. Journal (DB) ! ! ! Processor var count = 1 ! def processorId = “a” !
- 49. Journal (DB) ! ! ! Processor var count = 1 ! def processorId = “a” ! replay!
- 50. Journal (DB) ! ! ! Processor var count = 1 ! def processorId = “a” !
- 51. Journal (DB) ! ! ! Processor var count = 2 ! def processorId = “a” !
- 52. Journal (DB) ! ! ! Processor var count = 2 ! def processorId = “a” ! yay!
- 53. Processor import akka.persistence._! ! class CounterProcessor extends Processor {! var count = 0! override val processorId = "counter"! ! def receive = {! case Persistent(payload, seqNr) =>! // payload already persisted! count += 1! }! }
- 54. Processor import akka.persistence._! ! class CounterProcessor extends Processor {! var count = 0! override val processorId = "counter"! ! def receive = {! case Persistent(payload, seqNr) =>! // payload already persisted! count += 1! }! } counter ! Persistent(payload)
- 55. Processor import akka.persistence._! ! class CounterProcessor extends Processor {! var count = 0! override val processorId = "counter"! ! def receive = {! case Persistent(payload, seqNr) =>! // payload already persisted! count += 1! }! } counter ! Persistent(payload)
- 56. Processor import akka.persistence._! ! class CounterProcessor extends Processor {! var count = 0! override val processorId = "counter"! ! def receive = {! case Persistent(payload, seqNr) =>! // payload already persisted! count += 1! }! } counter ! Persistent(payload)
- 57. Processor import akka.persistence._! ! class CounterProcessor extends Processor {! var count = 0! override val processorId = "counter"! ! def receive = {! case Persistent(payload, seqNr) =>! // payload already persisted! count += 1! }! } counter ! Persistent(payload) is already persisted!
- 58. Processor import akka.persistence._! ! class CounterProcessor extends Processor {! var count = 0! override val processorId = "counter"! ! def receive = {! case Persistent(payload, seqNr) =>! // payload already persisted! count += 1! }! } counter ! Persistent(payload) sequenceNr (generated by akka) is already persisted!
- 59. Processor import akka.persistence._! ! class CounterProcessor extends Processor {! var count = 0! override val processorId = "counter"! ! def receive = {! case notPersisted =>! // will not replay this msg!! count += 1! }! } counter ! payload
- 60. Processor import akka.persistence._! ! class CounterProcessor extends Processor {! var count = 0! override val processorId = "counter"! ! def receive = {! case notPersisted =>! // will not replay this msg!! count += 1! }! } counter ! payload won’t persist
- 61. Processor import akka.persistence._! ! class CounterProcessor extends Processor {! var count = 0! override val processorId = "counter"! ! def receive = {! case notPersisted =>! // will not replay this msg!! count += 1! }! } counter ! payload won’t persist won’t replay
- 62. Processor import akka.persistence._! ! class CounterProcessor extends Processor {! var count = 0! override val processorId = "counter"! ! def receive = {! case Persistent(payload, seqNr) =>! // payload already persisted! count += 1! ! case notPersistentMsg =>! // msg not persisted - like in normal Actor! count += 1! }! }
- 63. Processor Upsides • Persistent Command Sourcing “out of the box” • Pretty simple, persist handled for you • Once you get the msg, it’s persisted • Pluggable Journals (HBase, Cassandra, Mongo, …) • Can replay to given seqNr (post-mortem etc!)
- 64. Processor Downsides • Exposes Persistent() to Actors who talk to you • No room for validation before persisting • There’s one Model, we act on the incoming msg • Lower throughput than plain Actor (limited by DB)
- 66. EventsourcedProcessor (longer name == more flexibility) ;-)
- 67. super quick domain modeling!
- 68. super quick domain modeling! sealed trait Command! case class ManyCommand(nums: List[Int]) extends Command Commands - input from user,“send emails”, not persisted
- 69. super quick domain modeling! sealed trait Command! case class ManyCommand(nums: List[Int]) extends Command Commands - input from user,“send emails”, not persisted sealed trait Event! case class AddOneEvent(num: Int) extends Event! Events - business events emitted by the processor, persisted
- 70. super quick domain modeling! sealed trait Command! case class ManyCommand(nums: List[Int]) extends Command Commands - input from user,“send emails”, not persisted case class State(count: Int) {! def updated(more: Int) = State(count + more)! } State - internal actor state, kept in var sealed trait Event! case class AddOneEvent(num: Int) extends Event! Events - business events emitted by the processor, persisted
- 71. var count = 0 ! def processorId = “a” ! EventsourcedProcessor ! ! Journal C1
- 72. var count = 0 ! def processorId = “a” ! EventsourcedProcessor Command ! ! Journal C1
- 73. var count = 0 ! def processorId = “a” ! EventsourcedProcessor ! ! Journal C1
- 74. var count = 0 ! def processorId = “a” ! EventsourcedProcessor ! ! Journal C1 Generate Events
- 75. C1 var count = 0 ! def processorId = “a” ! EventsourcedProcessor ! ! Journal E1
- 76. C1 var count = 0 ! def processorId = “a” ! EventsourcedProcessor ! ! Journal E1 Event
- 77. C1 var count = 0 ! def processorId = “a” ! EventsourcedProcessor ! ! Journal E1
- 78. C1 var count = 0 ! def processorId = “a” ! EventsourcedProcessor ! ! Journal E1 ACK “persisted”
- 79. C1 var count = 1 ! def processorId = “a” ! EventsourcedProcessor ! ! Journal E1 E1
- 80. C1 var count = 1 ! def processorId = “a” ! EventsourcedProcessor ! ! Journal E1 E1 “Apply” event
- 81. EventsourcedProcessor class MultiCounter extends EventsourcedProcessor {! ! var state = State(count = 0)! ! def updateState(e: Event): State = {! case event: AddOneEvent => state.updated(event.num)! }! ! // API:! ! def receiveCommand = ??? // TODO! ! def receiveRecover = ??? // TODO! ! }!
- 82. EventsourcedProcessor def receiveCommand = {! case ManyCommand(many) =>! for (event <- many map AddOneEvent)! persist(event) { state = updateState(_) }! ! case command: Command =>! persist(AddOneEvent(command)) { state = updateState(_) }! }
- 83. EventsourcedProcessor def receiveCommand = {! case ManyCommand(many) =>! for (event <- many map AddOneEvent)! persist(event) { state = updateState(_) }! ! case command: Command =>! persist(AddOneEvent(command)) { state = updateState(_) }! }
- 84. EventsourcedProcessor def receiveCommand = {! case ManyCommand(many) =>! for (event <- many map AddOneEvent)! persist(event) { state = updateState(_) }! ! case command: Command =>! persist(AddOneEvent(command)) { state = updateState(_) }! }
- 85. EventsourcedProcessor def receiveCommand = {! case ManyCommand(many) =>! for (event <- many map AddOneEvent)! persist(event) { state = updateState(_) }! ! case command: Command =>! persist(AddOneEvent(command)) { state = updateState(_) }! } async persist that event
- 86. EventsourcedProcessor def receiveCommand = {! case ManyCommand(many) =>! for (event <- many map AddOneEvent)! persist(event) { state = updateState(_) }! ! case command: Command =>! persist(AddOneEvent(command)) { state = updateState(_) }! } async persist that event async called after successful persist
- 87. EventsourcedProcessor def receiveCommand = {! case ManyCommand(many) =>! for (event <- many map AddOneEvent)! persist(event) { state = updateState(_) }! ! case command: Command =>! persist(AddOneEvent(command)) { state = updateState(_) }! } async persist that event async called after successful persist It is guaranteed that no new commands will be received by a processor between a call to `persist` and the execution of its `handler`.
- 88. EventsourcedProcessor def receiveCommand = {! case ManyCommand(many) =>! for (event <- many map AddOneEvent)! persist(event) { state = updateState(_) }! ! case command: Command =>! persist(AddOneEvent(command)) { state = updateState(_) }! }
- 89. EventsourcedProcessor case ManyCommand(many) =>! for (event <- many map AddOneEvent)! persist(event) { state = updateState(_) }
- 90. EventsourcedProcessor case ManyCommand(many) =>! for (event <- many map AddOneEvent)! persist(event) { state = updateState(_) } “style fix”
- 91. EventsourcedProcessor case ManyCommand(many) =>! for (event <- many map AddOneEvent)! persist(event) { state = updateState(_) } case ManyCommand(many) =>! persist(many map AddOneEvent) { state = updateState(_) } “style fix”
- 92. Eventsourced, recovery /** MUST NOT SIDE-EFFECT! */! def receiveRecover = {! case replayedEvent: Event => ! updateState(replayedEvent)! }
- 94. Eventsourced, snapshots /** MUST NOT SIDE-EFFECT! */! def receiveRecover = {! case SnapshotOffer(meta, snapshot: State) => ! this.state = state! ! case replayedEvent: Event => ! updateState(replayedEvent)! }
- 95. Eventsourced, snapshots /** MUST NOT SIDE-EFFECT! */! def receiveRecover = {! case SnapshotOffer(meta, snapshot: State) => ! this.state = state! ! case replayedEvent: Event => ! updateState(replayedEvent)! }
- 96. Eventsourced, snapshots /** MUST NOT SIDE-EFFECT! */! def receiveRecover = {! case SnapshotOffer(meta, snapshot: State) => ! this.state = state! ! case replayedEvent: Event => ! updateState(replayedEvent)! } snapshot!? how?
- 97. Eventsourced, snapshots def receiveCommand = {! case command: Command =>! saveSnapshot(state) // async!! } /** MUST NOT SIDE-EFFECT! */! def receiveRecover = {! case SnapshotOffer(meta, snapshot: State) => ! this.state = state! ! case replayedEvent: Event => ! updateState(replayedEvent)! } snapshot!? how?
- 98. Snapshots
- 100. …sum of states… Snapshots ! ! Journal E1 E2 E3 E4 E5 E6 E7 E8
- 101. state until [E8] Snapshots S8 ! ! Journal E1 E2 E3 E4 E5 E6 E7 E8
- 102. state until [E8] Snapshots S8 ! ! Snapshot Store snapshot! ! ! Journal E1 E2 E3 E4 E5 E6 E7 E8
- 103. state until [E8] Snapshots S8 ! ! Snapshot Store ! ! Journal E1 E2 E3 E4 E5 E6 E7 E8 S8
- 104. state until [E8] Snapshots S8 ! ! Snapshot Store ! ! Journal E1 E2 E3 E4 E5 E6 E7 E8 S8 crash!
- 105. Snapshots ! ! Snapshot Store ! ! Journal E1 E2 E3 E4 E5 E6 E7 E8 S8 crash!
- 106. “bring me up-to-date!” Snapshots ! ! Snapshot Store ! ! Journal E1 E2 E3 E4 E5 E6 E7 E8 S8 restart!
- 107. “bring me up-to-date!” Snapshots ! ! Snapshot Store ! ! Journal E1 E2 E3 E4 E5 E6 E7 E8 S8 restart! replay!
- 108. “bring me up-to-date!” Snapshots ! ! Snapshot Store S8 restart! replay! ! ! Journal E1 E2 E3 E4 E5 E6 E7 E8
- 109. “bring me up-to-date!” Snapshots ! ! Snapshot Store S8 restart! replay! ! ! Journal E1 E2 E3 E4 E5 E6 E7 E8
- 110. “bring me up-to-date!” Snapshots ! ! Snapshot Store S8 restart! replay! S8 ! ! Journal E1 E2 E3 E4 E5 E6 E7 E8
- 111. state until [E8] Snapshots ! ! Snapshot Store S8 restart! replay! S8 ! ! Journal E1 E2 E3 E4 E5 E6 E7 E8
- 112. state until [E8] Snapshots ! ! Snapshot Store S8 S8 ! ! Journal E1 E2 E3 E4 E5 E6 E7 E8
- 113. state until [E8] Snapshots ! ! Snapshot Store S8 S8 ! ! Journal E1 E2 E3 E4 E5 E6 E7 E8 We could delete these!
- 114. trait MySummer extends Processor {! var nums: List[Int]! var total: Int! ! def receive = {! case "snap" => saveSnapshot(total)! case SaveSnapshotSuccess(metadata) => // ...! case SaveSnapshotFailure(metadata, reason) => // ...! }! }! Snapshots, save
- 115. trait MySummer extends Processor {! var nums: List[Int]! var total: Int! ! def receive = {! case "snap" => saveSnapshot(total)! case SaveSnapshotSuccess(metadata) => // ...! case SaveSnapshotFailure(metadata, reason) => // ...! }! }! Snapshots, save Async!
- 116. trait MySummer extends Processor {! var nums: List[Int]! var total: Int! ! def receive = {! case "snap" => saveSnapshot(total)! case SaveSnapshotSuccess(metadata) => // ...! case SaveSnapshotFailure(metadata, reason) => // ...! }! }! Snapshots, success
- 117. trait MySummer extends Processor {! var nums: List[Int]! var total: Int! ! def receive = {! case "snap" => saveSnapshot(total)! case SaveSnapshotSuccess(metadata) => // ...! case SaveSnapshotFailure(metadata, reason) => // ...! }! }! Snapshots, success final case class SnapshotMetadata(! processorId: String, sequenceNr: Long, ! timestamp: Long)
- 118. trait MySummer extends Processor {! var nums: List[Int]! var total: Int! ! def receive = {! case "snap" => saveSnapshot(total)! case SaveSnapshotSuccess(metadata) => // ...! case SaveSnapshotFailure(metadata, reason) => // ...! }! }! Snapshots, success
- 119. Snapshot Recovery class Counter extends Processor {! var total = 0! ! def receive = {! case SnapshotOffer(metadata, snap: Int) => ! total = snap! ! case Persistent(payload, sequenceNr) => // ...! }! }
- 120. Snapshots Upsides • Simple! • Faster recovery (!) • Allows to delete “older” events • “known state at point in time”
- 121. Snapshots Downsides • More logic to write • Maybe not needed if events replay “fast enough” • Possibly “yet another database” to pick • snapshots are different than events, may be big!
- 122. Views
- 124. Journal (DB) ! ! ! Views ! Processor ! def processorId = “a” ! ! View ! def processorId = “a” ! ! !
- 125. Journal (DB) ! ! ! Views ! Processor ! def processorId = “a” ! ! View ! def processorId = “a” ! ! ! pooling
- 126. Journal (DB) ! ! ! Views ! Processor ! def processorId = “a” ! ! View ! def processorId = “a” ! ! ! pooling ! View ! def processorId = “a” ! ! ! pooling
- 127. Journal (DB) ! ! ! Views ! Processor ! def processorId = “a” ! ! View ! def processorId = “a” ! ! ! pooling ! View ! def processorId = “a” ! ! ! pooling different ActorPath, same processorId
- 128. View class DoublingCounterProcessor extends View {! var state = 0! override val processorId = "counter"! ! def receive = {! case Persistent(payload, seqNr) =>! // “state += 2 * payload” ! ! }! }
- 130. Akka Persistence Plugins Plugins are Community maintained! (“not sure how production ready”) http://akka.io/community/#journal_plugins
- 131. Akka Persistence Plugins Plugins are Community maintained! (“not sure how production ready”) http://akka.io/community/#journal_plugins • Journals - Cassandra, HBase, Mongo …
- 132. Akka Persistence Plugins Plugins are Community maintained! (“not sure how production ready”) http://akka.io/community/#journal_plugins • Journals - Cassandra, HBase, Mongo … • SnapshotStores - Cassandra, HDFS, HBase, Mongo …
- 134. Links • Official docs: http://doc.akka.io/docs/akka/2.3.0/scala/persistence.html • Patrik’s Slides & Webinar: http://www.slideshare.net/patriknw/akka- persistence-webinar • Papers: • Sagas http://www.cs.cornell.edu/andru/cs711/2002fa/reading/ sagas.pdf • Life beyond Distributed Transactions: http://www-db.cs.wisc.edu/ cidr/cidr2007/papers/cidr07p15.pdf • Pics: • http://misaspuppy.deviantart.com/art/Messenger-s-Cutie-Mark-A- Flying-Envelope-291040459
- 136. Links Eric Evans - “the DDD book” http://www.amazon.com/Domain-Driven-Design-Tackling-Complexity-Software/dp/0321125215 ! ! ! ! ! ! VaughnVernon’s Book and Talk http://www.amazon.com/Implementing-Domain-Driven-Design-Vaughn-Vernon/dp/0321834577 video: https://skillsmatter.com/skillscasts/4698-reactive-ddd-with-scala-and-akka ! ! !
- 137. ktoso @ typesafe.com twitter: ktosopl github: ktoso blog: project13.pl team blog: letitcrash.com Scalar 2014 @ Warsaw, PL ! Dzięki! Thanks! ありがとう！ ! ! ping me: