+per #18559 TCK tests for highestSequenceNr not reset after journal message deletion

* added tests
* docs about highestSeqenceNr behaviour after message deletion
* clarification about highestSequenceNr in AsyncRecovery#asyncReadHighestSequenceNr and AsyncWriteJournal#asyncDeleteMessagesTo

akka-docs/rst/java/persistence.rst

@@ -66,8 +66,8 @@ Architecture
   case of sender and receiver JVM crashes.
 
 * *AsyncWriteJournal*: A journal stores the sequence of messages sent to a persistent actor. An application can control which messages
-  are journaled and which are received by the persistent actor without being journaled. The storage backend of a journal is pluggable. 
-  Persistence extension comes with a "leveldb" journal plugin, which writes to the local filesystem, 
+  are journaled and which are received by the persistent actor without being journaled. Journal maintains *highestSequenceNr* that is increased on each message.
+  The storage backend of a journal is pluggable. Persistence extension comes with a "leveldb" journal plugin, which writes to the local filesystem,
   and replicated journals are available as `Community plugins`_.
 
 * *Snapshot store*: A snapshot store persists snapshots of a persistent actor's or a view's internal state. Snapshots are
@@ -354,6 +354,8 @@ while still having access to the accumulated state during replays - by loading t
 The result of the ``deleteMessages`` request is signaled to the persistent actor with a ``DeleteMessagesSuccess``
 message if the delete was successful or a ``DeleteMessagesFailure`` message if it failed.
 
+Message deletion doesn't affect highest sequence number of journal, even if all messages were deleted from journal after ``deleteMessages`` invocation.
+
 Persistence status handling
 ---------------------------
 Persisting, deleting and replaying messages can either succeed or fail.

akka-docs/rst/scala/persistence.rst

@@ -50,8 +50,8 @@ Architecture
   case of sender and receiver JVM crashes.
 
 * *AsyncWriteJournal*: A journal stores the sequence of messages sent to a persistent actor. An application can control which messages
-  are journaled and which are received by the persistent actor without being journaled. The storage backend of a journal is pluggable. 
-  Persistence extension comes with a "leveldb" journal plugin, which writes to the local filesystem, 
+  are journaled and which are received by the persistent actor without being journaled. Journal maintains *highestSequenceNr* that is increased on each message.
+  The storage backend of a journal is pluggable. Persistence extension comes with a "leveldb" journal plugin, which writes to the local filesystem,
   and replicated journals are available as `Community plugins`_.
 
 * *Snapshot store*: A snapshot store persists snapshots of a persistent actor's or a view's internal state. Snapshots are
@@ -341,6 +341,8 @@ while still having access to the accumulated state during replays - by loading t
 The result of the ``deleteMessages`` request is signaled to the persistent actor with a ``DeleteMessagesSuccess``
 message if the delete was successful or a ``DeleteMessagesFailure`` message if it failed.
 
+Message deletion doesn't affect highest sequence number of journal, even if all messages were deleted from journal after ``deleteMessages`` invocation.
+
 Persistence status handling
 ---------------------------
 Persisting, deleting and replaying messages can either succeed or fail.

akka-persistence-tck/src/main/scala/akka/persistence/journal/JournalSpec.scala

@@ -157,6 +157,31 @@ abstract class JournalSpec(config: Config) extends PluginSpec(config) {
       receiverProbe2.expectNoMsg(200.millis)
     }
 
+    "not reset highestSequenceNr after message deletion" in {
+      journal ! ReplayMessages(0, Long.MaxValue, Long.MaxValue, pid, receiverProbe.ref)
+      1 to 5 foreach { i ⇒ receiverProbe.expectMsg(replayedMessage(i)) }
+      receiverProbe.expectMsg(RecoverySuccess(highestSequenceNr = 5L))
+
+      journal ! DeleteMessagesTo(pid, 3L, receiverProbe.ref)
+      receiverProbe.expectMsg(DeleteMessagesSuccess(3L))
+
+      journal ! ReplayMessages(0, Long.MaxValue, Long.MaxValue, pid, receiverProbe.ref)
+      4 to 5 foreach { i ⇒ receiverProbe.expectMsg(replayedMessage(i)) }
+      receiverProbe.expectMsg(RecoverySuccess(highestSequenceNr = 5L))
+    }
+
+    "not reset highestSequenceNr after journal cleanup" in {
+      journal ! ReplayMessages(0, Long.MaxValue, Long.MaxValue, pid, receiverProbe.ref)
+      1 to 5 foreach { i ⇒ receiverProbe.expectMsg(replayedMessage(i)) }
+      receiverProbe.expectMsg(RecoverySuccess(highestSequenceNr = 5L))
+
+      journal ! DeleteMessagesTo(pid, Long.MaxValue, receiverProbe.ref)
+      receiverProbe.expectMsg(DeleteMessagesSuccess(Long.MaxValue))
+
+      journal ! ReplayMessages(0, Long.MaxValue, Long.MaxValue, pid, receiverProbe.ref)
+      receiverProbe.expectMsg(RecoverySuccess(highestSequenceNr = 5L))
+    }
+
     "reject non-serializable events" in {
       // there is no chance that a journal could create a data representation for type of event
       val notSerializableEvent = new Object { override def toString = "not serializable" }

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

@@ -51,6 +51,7 @@ trait AsyncRecovery {
    * number after recovery as the starting point when persisting new events.
    * This sequence number is also used as `toSequenceNr` in subsequent call
    * to [[#asyncReplayMessages]] unless the user has specified a lower `toSequenceNr`.
+   * Journal must maintain the highest sequence number and never decrease it.
    *
    * This call is protected with a circuit-breaker.
    *

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

@@ -215,6 +215,7 @@ trait AsyncWriteJournal extends Actor with WriteJournalBase with AsyncRecovery {
    * (inclusive).
    *
    * This call is protected with a circuit-breaker.
+   * Message deletion doesn't affect the highest sequence number of messages, journal must maintain the highest sequence number and never decrease it.
    */
   def asyncDeleteMessagesTo(persistenceId: String, toSequenceNr: Long): Future[Unit]