=cdd #17796 Avoid duplicate change events

akka-distributed-data/src/main/scala/akka/cluster/ddata/Replicator.scala

@@ -928,10 +928,16 @@ final class Replicator(settings: ReplicatorSettings) extends Actor with ActorLog
   }
 
   def setData(key: String, envelope: DataEnvelope): Unit = {
-    // notify subscribers, later
-    changed += key
+    val dig =
+      if (subscribers.contains(key) && !changed.contains(key)) {
+        val oldDigest = getDigest(key)
+        val dig = digest(envelope)
+        if (dig != oldDigest)
+          changed += key // notify subscribers, later
+        dig
+      } else if (envelope.data == DeletedData) DeletedDigest
+      else LazyDigest
 
-    val dig = if (envelope.data == DeletedData) DeletedDigest else LazyDigest
     dataEntries = dataEntries.updated(key, (envelope, dig))
   }
 
@@ -946,10 +952,12 @@ final class Replicator(settings: ReplicatorSettings) extends Actor with ActorLog
     }
   }
 
-  def digest(envelope: DataEnvelope): Digest = {
-    val bytes = serializer.toBinary(envelope)
-    ByteString.fromArray(MessageDigest.getInstance("SHA-1").digest(bytes))
-  }
+  def digest(envelope: DataEnvelope): Digest =
+    if (envelope.data == DeletedData) DeletedDigest
+    else {
+      val bytes = serializer.toBinary(envelope)
+      ByteString.fromArray(MessageDigest.getInstance("SHA-1").digest(bytes))
+    }
 
   def getData(key: String): Option[DataEnvelope] = dataEntries.get(key).map { case (envelope, _) ⇒ envelope }
 
@@ -1016,7 +1024,7 @@ final class Replicator(settings: ReplicatorSettings) extends Actor with ActorLog
   def receiveStatus(otherDigests: Map[String, Digest], chunk: Int, totChunks: Int): Unit = {
     if (log.isDebugEnabled)
       log.debug("Received gossip status from [{}], chunk [{}] of [{}] containing [{}]", sender().path.address,
-        chunk, totChunks, otherDigests.keys.mkString(", "))
+        (chunk + 1), totChunks, otherDigests.keys.mkString(", "))
 
     def isOtherDifferent(key: String, otherDigest: Digest): Boolean = {
       val d = getDigest(key)

akka-distributed-data/src/multi-jvm/scala/akka/cluster/ddata/ReplicatorSpec.scala

@@ -58,6 +58,7 @@ class ReplicatorSpec extends MultiNodeSpec(ReplicatorSpec) with STMultiNodeSpec
   val KeyF = GCounterKey("F")
   val KeyG = ORSetKey[String]("G")
   val KeyH = ORMapKey[Flag]("H")
+  val KeyI = GSetKey[String]("I")
   val KeyX = GCounterKey("X")
   val KeyY = GCounterKey("Y")
   val KeyZ = GCounterKey("Z")
@@ -525,5 +526,29 @@ class ReplicatorSpec extends MultiNodeSpec(ReplicatorSpec) with STMultiNodeSpec
     enterBarrier("after-9")
   }
 
+  "avoid duplicate change events for same data" in {
+    val changedProbe = TestProbe()
+    replicator ! Subscribe(KeyI, changedProbe.ref)
+    enterBarrier("subscribed-I")
+
+    runOn(second) {
+      replicator ! Update(KeyI, GSet.empty[String], writeTwo)(a ⇒ a.add("a"))
+    }
+
+    within(5.seconds) { // gossip to third
+      changedProbe.expectMsgPF() { case c @ Changed(KeyI) ⇒ c.get(KeyI).elements } should be(Set("a"))
+    }
+
+    enterBarrier("update-I")
+
+    runOn(first) {
+      replicator ! Update(KeyI, GSet.empty[String], writeTwo)(_ + "a")
+    }
+
+    changedProbe.expectNoMsg(1.second)
+
+    enterBarrier("after-10")
+  }
+
 }