!per Change for journal plugin compatibility

* A few more adjustments, found when verifying source compatibility of a few
  journal plugins
* Note that PersistentId will be removed with deleteMessage and we should
  not break plugins because of that
* Add missing section of at-least-once delivery in migration guide

(cherry picked from commit 6727eac6d07280d277968e2e25db44e02be3b102)

Conflicts:
	akka-persistence/src/main/scala/akka/persistence/JournalProtocol.scala
	akka-persistence/src/main/scala/akka/persistence/Persistent.scala
	akka-persistence/src/main/scala/akka/persistence/Snapshot.scala
	akka-persistence/src/main/scala/akka/persistence/journal/AsyncWriteProxy.scala

akka-docs/rst/java/code/docs/persistence/PersistencePluginDocTest.java

@@ -87,7 +87,7 @@ public class PersistencePluginDocTest {
         }
 
         @Override
-        public Future<Void> doAsyncDeleteMessages(Iterable<PersistenceId> messageIds, boolean permanent) {
+        public Future<Void> doAsyncDeleteMessages(Iterable<PersistentId> messageIds, boolean permanent) {
             return null;
         }
 

akka-docs/rst/project/migration-guide-persistence-experimental-2.3.x-2.4.x.rst

@@ -27,6 +27,8 @@ To extend ``PersistentActor``::
       /*...*/
     }
 
+Read more about the persistent actor in the :ref:`documentation for Scala <event-sourcing>` and 
+:ref:`documentation for Java <event-sourcing-java>`.
 
 Changed processorId to (abstract) persistenceId
 ===============================================
@@ -36,7 +38,7 @@ Persistent messages, as well as processors implemented the ``processorId`` metho
 This concept remains the same in Akka ``2.3.4``, yet we rename ``processorId`` to ``persistenceId`` because Processors will be removed,
 and persistent messages can be used from different classes not only ``PersistentActor`` (Views, directly from Journals etc).
 
-Please note that ``processorId`` is **abstract** in the new API classes (``PersistentActor`` and ``PersistentView``),
+Please note that ``persistenceId`` is **abstract** in the new API classes (``PersistentActor`` and ``PersistentView``),
 and we do **not** provide a default (actor-path derrived) value for it like we did for ``processorId``.
 The rationale behind this change being stricter de-coupling of your Actor hierarchy and the logical "which persistent entity this actor represents".
 A longer discussion on this subject can be found on `issue #15436 <https://github.com/akka/akka/issues/15436>`_ on github.
@@ -49,32 +51,6 @@ implement it yourself either as a helper trait or simply by overriding ``persist
 We provided the renamed method also on already deprecated classes (Channels),
 so you can simply apply a global rename of ``processorId`` to ``persistenceId``.
 
-Plugin APIs: Renamed PersistentId to PersistenceId
-==================================================
-Following the removal of Processors and moving to ``persistenceId``, the plugin SPI visible type has changed.
-The move from ``2.3.3`` to ``2.3.4`` should be relatively painless, and plugins will work even when using the deprecated ``PersistentId`` type.
-
-Change your implementations from::
-
-    def asyncWriteMessages(messages: immutable.Seq[PersistentRepr]): Future[Unit] = // ...
-
-    def asyncDeleteMessages(messageIds: immutable.Seq[PersistentId], permanent: Boolean): Future[Unit] = {
-      val p = messageIds.head.processorId // old
-      // ...
-    }
-
-to::
-
-    def asyncWriteMessages(messages: immutable.Seq[PersistentRepr]): Future[Unit] = // ...
-
-    def asyncDeleteMessages(messageIds: immutable.Seq[PersistenceId], permanent: Boolean): Future[Unit] = {
-      val p = messageIds.head.persistenceId // new
-      // ...
-    }
-
-Plugins written for ``2.3.3`` are source level compatible with ``2.3.4``, using the deprecated types, but will not work with future releases.
-Plugin maintainers are asked to update their plugins to ``2.3.4`` as soon as possible.
-
 Removed Processor in favour of extending PersistentActor with persistAsync
 ==========================================================================
 
@@ -110,7 +86,7 @@ Replacement code, with the same semantics, using PersistentActor::
           persistAsync(cmd) { e => sender() ! e }
       }
 
-      def receiveEvent = {
+      def receiveRecover = {
         case _ => // logic for handling replay
       }
     }
@@ -172,3 +148,24 @@ You should update it to extend ``PersistentView`` instead::
 In case you need to obtain the current sequence number the view is looking at, you can use the ``lastSequenceNr`` method.
 It is equivalent to "current sequence number", when ``isPersistent`` returns true, otherwise it yields the sequence number
 of the last persistent message that this view was updated with.
+
+Removed Channel and PersistentChannel in favour of AtLeastOnceDelivery trait
+============================================================================
+
+One of the primary tasks of a ``Channel`` was to de-duplicate messages that were sent from a
+``Processor`` during recovery. Performing external side effects during recovery is not 
+encouraged with event sourcing and therefore the ``Channel`` is not needed for this purpose.
+
+The ``Channel`` and ``PersistentChannel`` also performed at-least-once delivery of messages,
+but it did not free a sending actor from implementing retransmission or timeouts, since the 
+acknowledgement from the channel is needed to guarantee safe hand-off. Therefore at-least-once
+delivery is provided in a new ``AtLeastOnceDelivery`` trait that is mixed-in to the
+persistent actor on the sending side. 
+
+Read more about at-least-once delivery in the :ref:`documentation for Scala <at-least-once-delivery>` and 
+:ref:`documentation for Java <at-least-once-delivery-java>`.  
+
+
+
+
+   

akka-docs/rst/scala/code/docs/persistence/PersistencePluginDocSpec.scala

@@ -126,7 +126,7 @@ trait SharedLeveldbPluginDocSpec {
 class MyJournal extends AsyncWriteJournal {
   def asyncWriteMessages(messages: Seq[PersistentRepr]): Future[Unit] = ???
   def asyncWriteConfirmations(confirmations: Seq[PersistentConfirmation]): Future[Unit] = ???
-  def asyncDeleteMessages(messageIds: Seq[PersistenceId], permanent: Boolean): Future[Unit] = ???
+  def asyncDeleteMessages(messageIds: Seq[PersistentId], permanent: Boolean): Future[Unit] = ???
   def asyncDeleteMessagesTo(persistenceId: String, toSequenceNr: Long, permanent: Boolean): Future[Unit] = ???
   def asyncReplayMessages(persistenceId: String, fromSequenceNr: Long, toSequenceNr: Long, max: Long)(replayCallback: (PersistentRepr) => Unit): Future[Unit] = ???
   def asyncReadHighestSequenceNr(persistenceId: String, fromSequenceNr: Long): Future[Long] = ???

akka-persistence/src/main/java/akka/persistence/journal/japi/AsyncWritePlugin.java

@@ -32,7 +32,7 @@ interface AsyncWritePlugin {
      * 
      * @deprecated doAsyncDeleteMessages will be removed (since 2.3.4)
      */
-    @Deprecated Future<Void> doAsyncDeleteMessages(Iterable<PersistenceId> messageIds, boolean permanent);
+    @Deprecated Future<Void> doAsyncDeleteMessages(Iterable<PersistentId> messageIds, boolean permanent);
 
     /**
      * Java API, Plugin API: synchronously deletes all persistent messages up to

akka-persistence/src/main/java/akka/persistence/journal/japi/SyncWritePlugin.java

@@ -30,7 +30,7 @@ interface SyncWritePlugin {
      * 
      * @deprecated doDeleteMessages will be removed (since 2.3.4)
      */
-    @Deprecated void doDeleteMessages(Iterable<PersistenceId> messageIds, boolean permanent);
+    @Deprecated void doDeleteMessages(Iterable<PersistentId> messageIds, boolean permanent);
 
     /**
      * Java API, Plugin API: synchronously deletes all persistent messages up to

akka-persistence/src/main/scala/akka/persistence/JournalProtocol.scala

@@ -18,12 +18,12 @@ private[persistence] object JournalProtocol {
    * Request to delete messages identified by `messageIds`. If `permanent` is set to `false`,
    * the persistent messages are marked as deleted, otherwise they are permanently deleted.
    */
-  final case class DeleteMessages(messageIds: immutable.Seq[PersistenceId], permanent: Boolean, requestor: Option[ActorRef] = None)
+  final case class DeleteMessages(messageIds: immutable.Seq[PersistentId], permanent: Boolean, requestor: Option[ActorRef] = None)
 
   /**
    * Reply message to a successful [[DeleteMessages]] request.
    */
-  final case class DeleteMessagesSuccess(messageIds: immutable.Seq[PersistenceId])
+  final case class DeleteMessagesSuccess(messageIds: immutable.Seq[PersistentId])
 
   /**
    * Reply message to a failed [[DeleteMessages]] request.

akka-persistence/src/main/scala/akka/persistence/Persistent.scala

@@ -130,7 +130,7 @@ object ConfirmablePersistent {
  * During recovery, they are also replayed individually.
  */
 @deprecated("Use akka.persistence.PersistentActor instead", since = "2.3.4")
-case class PersistentBatch(batch: immutable.Seq[Resequenceable]) extends Message
+final case class PersistentBatch(batch: immutable.Seq[Resequenceable]) extends Message
 
 @deprecated("Use akka.persistence.PersistentActor instead", since = "2.3.4")
 object PersistentBatch {
@@ -155,26 +155,19 @@ trait PersistentConfirmation {
 
 /**
  * Plugin API: persistent message identifier.
- *
- * Deprecated, please use [[PersistenceId]].
  */
-@deprecated("Use PersistenceId instead.", since = "2.3.4")
+@deprecated("deleteMessages will be removed.", since = "2.3.4")
-trait PersistentId extends PersistenceId {
+trait PersistentId {
-  /**
-   * Persistent id that journals a persistent message
-   */
-  @deprecated("Use `persistenceId` instead.", since = "2.3.4")
-  def processorId: String = persistenceId
-}
 
   /**
- * Plugin API: persistent message identifier.
+   * Persistent id that journals a persistent message
    */
-trait PersistenceId {
+  def processorId: String
+
   /**
    * Persistent id that journals a persistent message
    */
-  def persistenceId: String
+  def persistenceId: String = processorId
 
   /**
    * A persistent message's sequence number.
@@ -185,7 +178,8 @@ trait PersistenceId {
 /**
  * INTERNAL API.
  */
-private[persistence] final case class PersistenceIdImpl(persistenceId: String, sequenceNr: Long) extends PersistenceId
+@deprecated("deleteMessages will be removed.", since = "2.3.4")
+private[persistence] final case class PersistentIdImpl(processorId: String, sequenceNr: Long) extends PersistentId
 
 /**
  * Plugin API: representation of a persistent message in the journal plugin API.
@@ -194,7 +188,7 @@ private[persistence] final case class PersistenceIdImpl(persistenceId: String, s
  * @see [[journal.AsyncWriteJournal]]
  * @see [[journal.AsyncRecovery]]
  */
-trait PersistentRepr extends Persistent with Resequenceable with PersistenceId with Message {
+trait PersistentRepr extends Persistent with Resequenceable with PersistentId with Message {
   // todo we want to get rid of the Persistent() wrapper from user land; PersistentRepr is here to stay. #15230
 
   import scala.collection.JavaConverters._
@@ -313,7 +307,7 @@ object PersistentRepr {
 private[persistence] final case class PersistentImpl(
   payload: Any,
   sequenceNr: Long,
-  @deprecatedName('processorId) persistenceId: String,
+  @deprecatedName('processorId) override val persistenceId: String,
   deleted: Boolean,
   confirms: immutable.Seq[String],
   sender: ActorRef) extends Persistent with PersistentRepr {
@@ -339,6 +333,9 @@ private[persistence] final case class PersistentImpl(
   val confirmable: Boolean = false
   val confirmMessage: Delivered = null
   val confirmTarget: ActorRef = null
+
+  @deprecated("Use persistenceId.", since = "2.3.4")
+  override def processorId = persistenceId
 }
 
 /**
@@ -348,7 +345,7 @@ private[persistence] final case class PersistentImpl(
 private[persistence] final case class ConfirmablePersistentImpl(
   payload: Any,
   sequenceNr: Long,
-  @deprecatedName('processorId) persistenceId: String,
+  @deprecatedName('processorId) override val persistenceId: String,
   deleted: Boolean,
   redeliveries: Int,
   confirms: immutable.Seq[String],
@@ -369,6 +366,9 @@ private[persistence] final case class ConfirmablePersistentImpl(
 
   def update(sequenceNr: Long, @deprecatedName('processorId) persistenceId: String, deleted: Boolean, redeliveries: Int, confirms: immutable.Seq[String], confirmMessage: Delivered, confirmTarget: ActorRef, sender: ActorRef) =
     copy(sequenceNr = sequenceNr, persistenceId = persistenceId, deleted = deleted, redeliveries = redeliveries, confirms = confirms, confirmMessage = confirmMessage, confirmTarget = confirmTarget, sender = sender)
+
+  @deprecated("Use persistenceId.", since = "2.3.4")
+  override def processorId = persistenceId
 }
 
 /**

akka-persistence/src/main/scala/akka/persistence/PersistentChannel.scala

@@ -205,9 +205,11 @@ final case class DeliveredByPersistentChannel(
   channelId: String,
   persistentSequenceNr: Long,
   deliverySequenceNr: Long = 0L,
-  channel: ActorRef = null) extends Delivered with PersistenceId {
+  channel: ActorRef = null) extends Delivered with PersistentId {
 
-  def persistenceId: String = channelId
+  override def persistenceId: String = channelId
+  @deprecated("Use persistenceId.", since = "2.3.4")
+  override def processorId = persistenceId
   def sequenceNr: Long = persistentSequenceNr
   def update(deliverySequenceNr: Long, channel: ActorRef): DeliveredByPersistentChannel =
     copy(deliverySequenceNr = deliverySequenceNr, channel = channel)

akka-persistence/src/main/scala/akka/persistence/Processor.scala

@@ -223,7 +223,7 @@ private[akka] trait ProcessorImpl extends Actor with Recovery {
    */
   @deprecated("deleteMessage(sequenceNr) will be removed. Instead, validate before persist, and use deleteMessages for pruning.", since = "2.3.4")
   def deleteMessage(sequenceNr: Long, permanent: Boolean): Unit = {
-    journal ! DeleteMessages(List(PersistenceIdImpl(persistenceId, sequenceNr)), permanent)
+    journal ! DeleteMessages(List(PersistentIdImpl(persistenceId, sequenceNr)), permanent)
   }
 
   /**

akka-persistence/src/main/scala/akka/persistence/Snapshot.scala

@@ -13,7 +13,10 @@ package akka.persistence
  * @param timestamp time at which the snapshot was saved.
  */
 @SerialVersionUID(1L) //#snapshot-metadata
-final case class SnapshotMetadata(@deprecatedName('processorId) persistenceId: String, sequenceNr: Long, timestamp: Long = 0L)
+final case class SnapshotMetadata(@deprecatedName('processorId) persistenceId: String, sequenceNr: Long, timestamp: Long = 0L) {
+  @deprecated("Use persistenceId instead.", since = "2.3.4")
+  def processorId: String = persistenceId
+}
 //#snapshot-metadata
 
 /**
@@ -120,7 +123,10 @@ private[persistence] object SnapshotProtocol {
    * @param criteria criteria for selecting a snapshot from which recovery should start.
    * @param toSequenceNr upper sequence number bound (inclusive) for recovery.
    */
-  final case class LoadSnapshot(@deprecatedName('processorId) persistenceId: String, criteria: SnapshotSelectionCriteria, toSequenceNr: Long)
+  final case class LoadSnapshot(@deprecatedName('processorId) persistenceId: String, criteria: SnapshotSelectionCriteria, toSequenceNr: Long) {
+    @deprecated("Use persistenceId instead.", since = "2.3.4")
+    def processorId: String = persistenceId
+  }
 
   /**
    * Response message to a [[LoadSnapshot]] message.
@@ -150,5 +156,8 @@ private[persistence] object SnapshotProtocol {
    * @param persistenceId persistent actor id.
    * @param criteria criteria for selecting snapshots to be deleted.
    */
-  final case class DeleteSnapshots(@deprecatedName('processorId) persistenceId: String, criteria: SnapshotSelectionCriteria)
+  final case class DeleteSnapshots(@deprecatedName('processorId) persistenceId: String, criteria: SnapshotSelectionCriteria) {
+    @deprecated("Use persistenceId instead.", since = "2.3.4")
+    def processorId: String = persistenceId
+  }
 }

akka-persistence/src/main/scala/akka/persistence/journal/AsyncWriteJournal.scala

@@ -105,7 +105,7 @@ trait AsyncWriteJournal extends Actor with WriteJournalBase with AsyncRecovery {
    * deleted, otherwise they are permanently deleted.
    */
   @deprecated("asyncDeleteMessages will be removed.", since = "2.3.4")
-  def asyncDeleteMessages(messageIds: immutable.Seq[PersistenceId], permanent: Boolean): Future[Unit]
+  def asyncDeleteMessages(messageIds: immutable.Seq[PersistentId], permanent: Boolean): Future[Unit]
 
   /**
    * Plugin API: asynchronously deletes all persistent messages up to `toSequenceNr`

akka-persistence/src/main/scala/akka/persistence/journal/AsyncWriteProxy.scala

@@ -43,7 +43,7 @@ private[persistence] trait AsyncWriteProxy extends AsyncWriteJournal with Stash
   def asyncWriteConfirmations(confirmations: immutable.Seq[PersistentConfirmation]): Future[Unit] =
     (store ? WriteConfirmations(confirmations)).mapTo[Unit]
 
-  def asyncDeleteMessages(messageIds: immutable.Seq[PersistenceId], permanent: Boolean): Future[Unit] =
+  def asyncDeleteMessages(messageIds: immutable.Seq[PersistentId], permanent: Boolean): Future[Unit] =
     (store ? DeleteMessages(messageIds, permanent)).mapTo[Unit]
 
   def asyncDeleteMessagesTo(persistenceId: String, toSequenceNr: Long, permanent: Boolean): Future[Unit] =
@@ -78,7 +78,7 @@ private[persistence] object AsyncWriteTarget {
   final case class WriteConfirmations(confirmations: immutable.Seq[PersistentConfirmation])
 
   @SerialVersionUID(1L)
-  final case class DeleteMessages(messageIds: immutable.Seq[PersistenceId], permanent: Boolean)
+  final case class DeleteMessages(messageIds: immutable.Seq[PersistentId], permanent: Boolean)
 
   @SerialVersionUID(1L)
   final case class DeleteMessagesTo(persistenceId: String, toSequenceNr: Long, permanent: Boolean)

akka-persistence/src/main/scala/akka/persistence/journal/SyncWriteJournal.scala

@@ -97,7 +97,7 @@ trait SyncWriteJournal extends Actor with WriteJournalBase with AsyncRecovery {
    * deleted, otherwise they are permanently deleted.
    */
   @deprecated("deleteMessages will be removed.", since = "2.3.4")
-  def deleteMessages(messageIds: immutable.Seq[PersistenceId], permanent: Boolean): Unit
+  def deleteMessages(messageIds: immutable.Seq[PersistentId], permanent: Boolean): Unit
 
   /**
    * Plugin API: synchronously deletes all persistent messages up to `toSequenceNr`

akka-persistence/src/main/scala/akka/persistence/journal/inmem/InmemJournal.scala

@@ -34,7 +34,7 @@ private[persistence] class InmemJournal extends AsyncWriteProxy {
  * INTERNAL API.
  */
 private[persistence] trait InmemMessages {
-  // persistentActorId -> persistent message
+  // persistenceId -> persistent message
   var messages = Map.empty[String, Vector[PersistentRepr]]
 
   def add(p: PersistentRepr) = messages = messages + (messages.get(p.persistenceId) match {

akka-persistence/src/main/scala/akka/persistence/journal/japi/AsyncWriteJournal.scala

@@ -22,7 +22,7 @@ abstract class AsyncWriteJournal extends AsyncRecovery with SAsyncWriteJournal w
   final def asyncWriteConfirmations(confirmations: immutable.Seq[PersistentConfirmation]) =
     doAsyncWriteConfirmations(confirmations.asJava).map(Unit.unbox)
 
-  final def asyncDeleteMessages(messageIds: immutable.Seq[PersistenceId], permanent: Boolean) =
+  final def asyncDeleteMessages(messageIds: immutable.Seq[PersistentId], permanent: Boolean) =
     doAsyncDeleteMessages(messageIds.asJava, permanent).map(Unit.unbox)
 
   final def asyncDeleteMessagesTo(persistenceId: String, toSequenceNr: Long, permanent: Boolean) =

akka-persistence/src/main/scala/akka/persistence/journal/japi/SyncWriteJournal.scala

@@ -20,7 +20,7 @@ abstract class SyncWriteJournal extends AsyncRecovery with SSyncWriteJournal wit
   final def writeConfirmations(confirmations: immutable.Seq[PersistentConfirmation]) =
     doWriteConfirmations(confirmations.asJava)
 
-  final def deleteMessages(messageIds: immutable.Seq[PersistenceId], permanent: Boolean) =
+  final def deleteMessages(messageIds: immutable.Seq[PersistentId], permanent: Boolean) =
     doDeleteMessages(messageIds.asJava, permanent)
 
   final def deleteMessagesTo(persistenceId: String, toSequenceNr: Long, permanent: Boolean) =

akka-persistence/src/main/scala/akka/persistence/journal/leveldb/LeveldbStore.scala

@@ -46,7 +46,7 @@ private[persistence] trait LeveldbStore extends Actor with LeveldbIdMapping with
   def writeConfirmations(confirmations: immutable.Seq[PersistentConfirmation]) =
     withBatch(batch ⇒ confirmations.foreach(confirmation ⇒ addToConfirmationBatch(confirmation, batch)))
 
-  def deleteMessages(messageIds: immutable.Seq[PersistenceId], permanent: Boolean) = withBatch { batch ⇒
+  def deleteMessages(messageIds: immutable.Seq[PersistentId], permanent: Boolean) = withBatch { batch ⇒
     messageIds foreach { messageId ⇒
       if (permanent) batch.delete(keyToBytes(Key(numericId(messageId.persistenceId), messageId.sequenceNr, 0)))
       else batch.put(keyToBytes(deletionKey(numericId(messageId.persistenceId), messageId.sequenceNr)), Array.emptyByteArray)

akka-persistence/src/test/scala/akka/persistence/journal/chaos/ChaosJournal.scala

@@ -24,7 +24,7 @@ class ReplayFailedException(ps: Seq[PersistentRepr])
 class ReadHighestFailedException
   extends TestException(s"recovery failed when reading highest sequence number")
 
-class DeleteFailedException(messageIds: immutable.Seq[PersistenceId])
+class DeleteFailedException(messageIds: immutable.Seq[PersistentId])
   extends TestException(s"delete failed for message ids = [${messageIds}]")
 
 /**
@@ -53,13 +53,13 @@ class ChaosJournal extends SyncWriteJournal {
     if (shouldFail(confirmFailureRate)) throw new ConfirmFailedException(confirmations)
     else confirmations.foreach(cnf ⇒ update(cnf.persistenceId, cnf.sequenceNr)(p ⇒ p.update(confirms = cnf.channelId +: p.confirms)))
 
-  def deleteMessages(messageIds: immutable.Seq[PersistenceId], permanent: Boolean): Unit =
+  def deleteMessages(messageIds: immutable.Seq[PersistentId], permanent: Boolean): Unit =
     if (shouldFail(deleteFailureRate)) throw new DeleteFailedException(messageIds)
     else if (permanent) messageIds.foreach(mid ⇒ update(mid.persistenceId, mid.sequenceNr)(_.update(deleted = true)))
     else messageIds.foreach(mid ⇒ del(mid.persistenceId, mid.sequenceNr))
 
   def deleteMessagesTo(persistenceId: String, toSequenceNr: Long, permanent: Boolean): Unit =
-    (1L to toSequenceNr).map(PersistenceIdImpl(persistenceId, _))
+    (1L to toSequenceNr).map(PersistentIdImpl(persistenceId, _))
 
   def asyncReplayMessages(persistenceId: String, fromSequenceNr: Long, toSequenceNr: Long, max: Long)(replayCallback: (PersistentRepr) ⇒ Unit): Future[Unit] =
     if (shouldFail(replayFailureRate)) {

akka-samples/akka-sample-persistence-java-lambda/src/main/java/doc/LambdaPersistencePluginDocTest.java

@@ -87,7 +87,7 @@ public class LambdaPersistencePluginDocTest {
     }
 
     @Override
-    public Future<Void> doAsyncDeleteMessages(Iterable<PersistenceId> messageIds, boolean permanent) {
+    public Future<Void> doAsyncDeleteMessages(Iterable<PersistentId> messageIds, boolean permanent) {
       return null;
     }
 

akka-samples/akka-sample-persistence-java-lambda/src/main/java/sample/persistence/SnapshotExample.java

@@ -9,7 +9,6 @@ import akka.actor.ActorSystem;
 import akka.actor.Props;
 import akka.japi.pf.ReceiveBuilder;
 import akka.persistence.AbstractPersistentActor;
-import akka.persistence.Persistent;
 import akka.persistence.SnapshotOffer;
 import scala.PartialFunction;
 import scala.runtime.BoxedUnit;