Akka-persistence-inmemory is a plugin for akka-persistence that writes journal and snapshot entries entries to an in-memory store. It is very useful for testing your persistent actors.

Service	Status	Description
License		Apache 2.0
Bintray		Latest Version on Bintray

Add the following to your build.sbt:

// the library is available in Bintray's JCenter
resolvers += Resolver.jcenterRepo

libraryDependencies += "com.github.dnvriend" %% "akka-persistence-inmemory" % "1.3.0"

Add the following to the application.conf:

akka {
  persistence {
    journal.plugin = "inmemory-journal"
    snapshot-store.plugin = "inmemory-snapshot-store"
  }
}

The query API can be configured by overriding the defaults by placing the following in application.conf:

# Optional
inmemory-read-journal {
  # New events are retrieved (polled) with this interval.
  refresh-interval = "1s"

  # How many events to fetch in one query (replay) and keep buffered until they
  # are delivered downstreams.
  max-buffer-size = "500"
}

The async query API uses polling to query the journal for new events. The refresh interval can be configured eg. "1s" so that the journal will be polled every 1 second. This setting is global for each async query, so the allPersistenceId, eventsByTag and eventsByPersistenceId queries.

When an async query is started, a number of events will be buffered and will use memory when not consumed by a Sink. The default size is 500.

The ReadJournal is retrieved via the akka.persistence.query.PersistenceQuery extension:

import akka.persistence.query.PersistenceQuery
import akka.persistence.inmemory.query.journal.scaladsl.InMemoryReadJournal
 
val readJournal: InMemoryReadJournal = PersistenceQuery(system).readJournalFor[InMemoryReadJournal](InMemoryReadJournal.Identifier)

The ReadJournal is retrieved via the akka.persistence.query.PersistenceQuery extension:

import akka.persistence.query.PersistenceQuery
import akka.persistence.inmemory.query.journal.javadsl.InMemoryReadJournal

final InMemoryReadJournal readJournal = PersistenceQuery.get(system).getReadJournalFor(InMemoryReadJournal.class, InMemoryReadJournal.Identifier());

The plugin supports the following queries:

allPersistenceIds and currentPersistenceIds are used for retrieving all persistenceIds of all persistent actors.

import akka.actor.ActorSystem
import akka.stream.{Materializer, ActorMaterializer}
import akka.stream.scaladsl.Source
import akka.persistence.query.PersistenceQuery
import akka.persistence.inmemory.query.journal.scaladsl.InMemoryReadJournal

implicit val system: ActorSystem = ActorSystem()
implicit val mat: Materializer = ActorMaterializer()(system)
val readJournal: InMemoryReadJournal = PersistenceQuery(system).readJournalFor[InMemoryReadJournal](InMemoryReadJournal.Identifier)

val willNotCompleteTheStream: Source[String, NotUsed] = readJournal.allPersistenceIds()

val willCompleteTheStream: Source[String, NotUsed] = readJournal.currentPersistenceIds()

The returned event stream is unordered and you can expect different order for multiple executions of the query.

When using the allPersistenceIds query, the stream is not completed when it reaches the end of the currently used persistenceIds, but it continues to push new persistenceIds when new persistent actors are created.

When using the currentPersistenceIds query, the stream is completed when the end of the current list of persistenceIds is reached, thus it is not a live query.

The stream is completed with failure if there is a failure in executing the query in the backend journal.

eventsByPersistenceId and currentEventsByPersistenceId is used for retrieving events for a specific PersistentActor identified by persistenceId.

import akka.actor.ActorSystem
import akka.stream.{Materializer, ActorMaterializer}
import akka.stream.scaladsl.Source
import akka.persistence.query.{ PersistenceQuery, EventEnvelope }
import akka.persistence.inmemory.query.journal.scaladsl.InMemoryReadJournal

implicit val system: ActorSystem = ActorSystem()
implicit val mat: Materializer = ActorMaterializer()(system)
val readJournal: InMemoryReadJournal = PersistenceQuery(system).readJournalFor[InMemoryReadJournal](InMemoryReadJournal.Identifier)

val willNotCompleteTheStream: Source[EventEnvelope, NotUsed] = readJournal.eventsByPersistenceId("some-persistence-id", 0L, Long.MaxValue)

val willCompleteTheStream: Source[EventEnvelope, NotUsed] = readJournal.currentEventsByPersistenceId("some-persistence-id", 0L, Long.MaxValue)

You can retrieve a subset of all events by specifying fromSequenceNr and toSequenceNr or use 0L and Long.MaxValue respectively to retrieve all events. Note that the corresponding sequence number of each event is provided in the EventEnvelope, which makes it possible to resume the stream at a later point from a given sequence number.

The returned event stream is ordered by sequence number, i.e. the same order as the PersistentActor persisted the events. The same prefix of stream elements (in same order) are returned for multiple executions of the query, except for when events have been deleted.

The stream is completed with failure if there is a failure in executing the query in the backend journal.

eventsByTag and currentEventsByTag are used for retrieving events that were marked with a given tag, e.g. all domain events of an Aggregate Root type.

import akka.actor.ActorSystem
import akka.stream.{Materializer, ActorMaterializer}
import akka.stream.scaladsl.Source
import akka.persistence.query.{ PersistenceQuery, EventEnvelope }
import akka.persistence.inmemory.query.journal.scaladsl.InMemoryReadJournal

implicit val system: ActorSystem = ActorSystem()
implicit val mat: Materializer = ActorMaterializer()(system)
val readJournal: InMemoryReadJournal = PersistenceQuery(system).readJournalFor[InMemoryReadJournal](InMemoryReadJournal.Identifier)

val willNotCompleteTheStream: Source[EventEnvelope, NotUsed] = readJournal.eventsByTag("apple", 0L)

val willCompleteTheStream: Source[EventEnvelope, NotUsed] = readJournal.currentEventsByTag("apple", 0L)

To tag events you'll need to create an Event Adapter that will wrap the event in a akka.persistence.journal.Tagged class with the given tags. The Tagged class will instruct the persistence plugin to tag the event with the given set of tags. The persistence plugin will not store the Tagged class in the journal. It will strip the tags and payload from the Tagged class, and use the class only as an instruction to tag the event with the given tags and store the payload in the message field of the journal table.

import akka.persistence.journal.{ Tagged, WriteEventAdapter }
import com.github.dnvriend.Person.{ LastNameChanged, FirstNameChanged, PersonCreated }

class TaggingEventAdapter extends WriteEventAdapter {
  override def manifest(event: Any): String = ""

  def withTag(event: Any, tag: String) = Tagged(event, Set(tag))

  override def toJournal(event: Any): Any = event match {
    case _: PersonCreated ⇒
      withTag(event, "person-created")
    case _: FirstNameChanged ⇒
      withTag(event, "first-name-changed")
    case _: LastNameChanged ⇒
      withTag(event, "last-name-changed")
    case _ ⇒ event
  }
}

The EventAdapter must be registered by adding the following to the root of application.conf Please see the demo-akka-persistence-jdbc project for more information. The identifier of the persistence plugin must be used which for the inmemory plugin is inmemory-journal.

inmemory-journal {
  event-adapters {
    tagging = "com.github.dnvriend.TaggingEventAdapter"
  }
  event-adapter-bindings {
    "com.github.dnvriend.Person$PersonCreated" = tagging
    "com.github.dnvriend.Person$FirstNameChanged" = tagging
    "com.github.dnvriend.Person$LastNameChanged" = tagging
  }
}

You can retrieve a subset of all events by specifying offset, or use 0L to retrieve all events with a given tag. The offset corresponds to an ordered sequence number for the specific tag. Note that the corresponding offset of each event is provided in the EventEnvelope, which makes it possible to resume the stream at a later point from a given offset.

In addition to the offset the EventEnvelope also provides persistenceId and sequenceNr for each event. The sequenceNr is the sequence number for the persistent actor with the persistenceId that persisted the event. The persistenceId + sequenceNr is an unique identifier for the event.

The returned event stream contains only events that correspond to the given tag, and is ordered by the creation time of the events, The same stream elements (in same order) are returned for multiple executions of the same query. Deleted events are not deleted from the tagged event stream.

• Removed the queries eventsByPersistenceIdAndTag and currentEventsByPersistenceIdAndTag as they are not supported by Akka natively and can be configured by filtering the event stream.
• Implemented true async queries using the polling strategy

• Akka 2.4.6 -> 2.4.7

• Fixed issue Unable to differentiate between persistence failures and serialization issues
• Akka 2.4.4 -> 2.4.6

• Akka 2.4.3 -> 2.4.4

• Scala 2.11.7 -> 2.11.8
• Akka 2.4.2 -> 2.4.3

• Fixed issue on the query api where the offset on eventsByTag and eventsByPersistenceIdAndTag queries were not sequential

• Refactored the akka-persistence-query interfaces, integrated it back again in one jar, for jcenter deployment simplicity

• Added the appropriate Maven POM resources to be publishing to Bintray's JCenter

• Fix for propagating serialization errors to akka-persistence so that any error regarding the persistence of messages will be handled by the callback handler of the Persistent Actor; onPersistFailure.

• Better storage implementation for journal and snapshot

• Akka 2.4.2-RC3 -> 2.4.2

• akka-persistence-jdbc-query 1.0.0 -> 1.0.1

• Akka 2.4.2-RC2 -> 2.4.2-RC3

• Compatibility with Akka 2.4.2-RC2
• Refactored the akka-persistence-query extension interfaces to its own jar: "com.github.dnvriend" %% "akka-persistence-jdbc-query" % "1.0.0"

• Code is based on akka-persistence-jdbc
• Supports the following queries:
  • allPersistenceIds and currentPersistenceIds
  • eventsByPersistenceId and currentEventsByPersistenceId
  • eventsByTag and currentEventsByTag
  • eventsByPersistenceIdAndTag and currentEventsByPersistenceIdAndTag

• Supports for the javadsl query API

• Compatibility with Akka 2.4.2-RC1

• Compatibility with Akka 2.4.1
• Merged PR #17 Evgeny Shepelyuk Upgrade to AKKA 2.4.1, thanks!

• Compatibility with Akka 2.4.0
• Merged PR #13 Evgeny Shepelyuk HighestSequenceNo should be kept on message deletion, thanks!
• Should be a fix for Issue #13 - HighestSequenceNo should be kept on message deletion as per Akka issue #18559

• Compatibility with Akka 2.4.0
• Merged PR #12 Evgeny Shepelyuk Live version of eventsByPersistenceId, thanks!

• Compatibility with Akka 2.4.0
• Akka 2.4.0-RC3 -> 2.4.0

• Merged PR #10 Evgeny Shepelyuk Live version of allPersistenceIds, thanks!
• Compatibility with Akka 2.4.0-RC3
• Use the following library dependency: "com.github.dnvriend" %% "akka-persistence-inmemory" % "1.1.3-RC3"

• Merged Issue #9 Evgeny Shepelyuk Initial implemenation of Persistence Query for In Memory journal, thanks!
• Compatibility with Akka 2.4.0-RC3
• Use the following library dependency: "com.github.dnvriend" %% "akka-persistence-inmemory" % "1.1.1-RC3"

• Merged Issue #6 Evgeny Shepelyuk Conditional ability to perform full serialization while adding messages to journal, thanks!
• Compatibility with Akka 2.4.0-RC3
• Use the following library dependency: "com.github.dnvriend" %% "akka-persistence-inmemory" % "1.1.0-RC3"

• Compatibility with Akka 2.4.0-RC2
• Use the following library dependency: "com.github.dnvriend" %% "akka-persistence-inmemory" % "1.1.0-RC2"

• Compatibilty with Akka 2.3.13
• Akka 2.3.12 -> 2.3.13

• Compatibility with Akka 2.4.0-RC1
• Use the following library dependency: "com.github.dnvriend" %% "akka-persistence-inmemory" % "1.1.0-RC1"

• Scala 2.11.6 -> 2.11.7
• Akka 2.3.11 -> 2.3.12
• Apache-2.0 license

• Merged Issue #2 Sebastián Ortega Regression: Fix corner case when persisted events are deleted, thanks!
• Added test for the corner case issue #1 and #2

• Refactored from the ConcurrentHashMap implementation to a pure Actor managed concurrency model

• Some refactoring, fixed some misconceptions about the behavior of Scala Futures one year ago :)
• Akka 2.3.6 -> 2.3.11
• Scala 2.11.1 -> 2.11.6
• Scala 2.10.4 -> 2.10.5
• Merged Issue #1 Sebastián Ortega Fix corner case when persisted events are deleted, thanks!

• Moved to bintray

• Akka 2.3.4 -> 2.3.6

• Initial Release

Contributors all agree to follow the W3C Code of Ethics and Professional Conduct.

If you want to take action, feel free to contact Dennis Vriend [email protected]. You can also contact W3C Staff as explained in W3C Procedures.

This source code is made available under the Apache 2.0 License. The quick summary of what this license means is available here

Have fun!