!per #3704 Persistence improvements

- Channel enhancements (#3773):
- Live read models (#3776):
- Batch-oriented journal plugin API (#3804):
- Batching of confirmations and deletions
- Message deletion enhancements (more efficient range deletions)

akka-samples/akka-sample-persistence/src/main/scala/sample/persistence/ViewExample.scala

@@ -0,0 +1,71 @@
+/**
+ * Copyright (C) 2009-2013 Typesafe Inc. <http://www.typesafe.com>
+ */
+
+package sample.persistence
+
+import akka.actor._
+import akka.persistence._
+
+object ViewExample extends App {
+  class ExampleProcessor extends Processor {
+    override def processorId = "processor-5"
+
+    def receive = {
+      case Persistent(payload, sequenceNr) =>
+        println(s"processor received ${payload} (sequence nr = ${sequenceNr})")
+    }
+  }
+
+  class ExampleView extends View {
+    private var numReplicated = 0
+
+    override def processorId = "processor-5"
+    override def viewId = "view-5"
+
+    private val destination = context.actorOf(Props[ExampleDestination])
+    private val channel = context.actorOf(Channel.props("channel"))
+
+    def receive = {
+      case "snap" =>
+        saveSnapshot(numReplicated)
+      case SnapshotOffer(metadata, snapshot: Int) =>
+        numReplicated = snapshot
+        println(s"view received snapshot offer ${snapshot} (metadata = ${metadata})")
+      case Persistent(payload, sequenceNr) =>
+        numReplicated += 1
+        println(s"view received ${payload} (sequence nr = ${sequenceNr}, num replicated = ${numReplicated})")
+        channel ! Deliver(Persistent(s"replicated-${payload}"), destination.path)
+    }
+  }
+
+  class ExampleDestination extends Actor {
+    def receive = {
+      case cp @ ConfirmablePersistent(payload, sequenceNr, _) =>
+        println(s"destination received ${payload} (sequence nr = ${sequenceNr})")
+        cp.confirm()
+    }
+  }
+
+  val system = ActorSystem("example")
+
+  val processor = system.actorOf(Props(classOf[ExampleProcessor]))
+  val view = system.actorOf(Props(classOf[ExampleView]))
+
+  @annotation.tailrec
+  def read(line: String): Unit = line match {
+    case "exit" | null =>
+    case "sync" =>
+      view ! Update(await = false)
+      read(Console.readLine())
+    case "snap" =>
+      view ! "snap"
+      read(Console.readLine())
+    case msg =>
+      processor ! Persistent(msg)
+      read(Console.readLine())
+  }
+
+  read(Console.readLine())
+  system.shutdown()
+}