Merge pull request #1764 from akka/wip-3660-simple-speedup-of-gossip-in-early-phase-ban

=clu #3660 Simple speedup of gossip in early phase

akka-cluster/src/main/scala/akka/cluster/ClusterDaemon.scala

@@ -111,6 +111,8 @@ private[cluster] object InternalClusterAction {
 
   case object GossipTick extends Tick
 
+  case object GossipSpeedupTick extends Tick
+
   case object HeartbeatTick extends Tick
 
   case object ReapUnreachableTick extends Tick
@@ -334,7 +336,8 @@ private[cluster] class ClusterCoreDaemon(publisher: ActorRef) extends Actor with
   def initialized: Actor.Receive = {
     case msg: GossipEnvelope              ⇒ receiveGossip(msg)
     case msg: GossipStatus                ⇒ receiveGossipStatus(msg)
-    case GossipTick                       ⇒ gossip()
+    case GossipTick                       ⇒ gossipTick()
+    case GossipSpeedupTick                ⇒ gossipSpeedupTick()
     case ReapUnreachableTick              ⇒ reapUnreachableMembers()
     case LeaderActionsTick                ⇒ leaderActions()
     case PublishStatsTick                 ⇒ publishInternalStats()
@@ -680,7 +683,19 @@ private[cluster] class ClusterCoreDaemon(publisher: ActorRef) extends Actor with
     }
   }
 
-  def mergeRate(count: Long): Double = (count * 1000.0) / GossipInterval.toMillis
+  def gossipTick(): Unit = {
+    gossip()
+    if (isGossipSpeedupNeeded) {
+      scheduler.scheduleOnce(GossipInterval / 3, self, GossipSpeedupTick)
+      scheduler.scheduleOnce(GossipInterval * 2 / 3, self, GossipSpeedupTick)
+    }
+  }
+
+  def gossipSpeedupTick(): Unit =
+    if (isGossipSpeedupNeeded) gossip()
+
+  def isGossipSpeedupNeeded: Boolean =
+    (latestGossip.overview.seen.size < latestGossip.members.size / 2)
 
   /**
    * Initiates a new round of gossip.