Update Persistence Snapshot documentation (#22419)

* Update Persistence Snapshot documentation (#22233)

* Use copy of ExampleState as it is mutable

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

@@ -234,13 +234,14 @@ public class LambdaPersistenceDocTest {
   static Object o4 = new Object() {
     class MyPersistentActor extends AbstractPersistentActor {
 
+      private void updateState(String evt){}
+
       //#save-snapshot
       private Object state;
+      private int snapShotInterval = 1000;
 
       @Override public Receive createReceive() {
         return receiveBuilder().
-          match(String.class, s -> s.equals("snap"),
-            s -> saveSnapshot(state)).
           match(SaveSnapshotSuccess.class, ss -> {
             SnapshotMetadata metadata = ss.metadata();
             // ...
@@ -248,6 +249,13 @@ public class LambdaPersistenceDocTest {
           match(SaveSnapshotFailure.class, sf -> {
             SnapshotMetadata metadata = sf.metadata();
             // ...
+          }).
+          match(String.class, cmd -> {
+            persist( "evt-" + cmd, e -> {
+              updateState(e);
+              if (lastSequenceNr() % snapShotInterval == 0 && lastSequenceNr() != 0)
+                saveSnapshot(state);
+            });
           }).build();
       }
       //#save-snapshot

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

@@ -76,6 +76,7 @@ class ExampleState implements Serializable {
 class ExamplePersistentActor extends AbstractPersistentActor {
 
     private ExampleState state = new ExampleState();
+    private int snapShotInterval = 1000;
 
     public int getNumEvents() {
         return state.size();
@@ -97,16 +98,15 @@ class ExamplePersistentActor extends AbstractPersistentActor {
         return receiveBuilder()
             .match(Cmd.class, c -> {
               final String data = c.getData();
-              final Evt evt1 = new Evt(data + "-" + getNumEvents());
+              final Evt evt = new Evt(data + "-" + getNumEvents());
-              final Evt evt2 = new Evt(data + "-" + (getNumEvents() + 1));
+              persist(evt, (Evt e) -> {
-              persistAll(asList(evt1, evt2), (Evt evt) -> {
+                  state.update(e);
-                state.update(evt);
+                  getContext().system().eventStream().publish(e);
-                if (evt.equals(evt2)) {
+                  if (lastSequenceNr() % snapShotInterval == 0 && lastSequenceNr() != 0)
-                  getContext().system().eventStream().publish(evt);
+                      // IMPORTANT: create a copy of snapshot because ExampleState is mutable
-                }
+                      saveSnapshot(state.copy());
               });
             })
-            .matchEquals("snap", s -> saveSnapshot(state.copy()))
             .matchEquals("print", s -> System.out.println(state))
             .build();
     }
@@ -120,7 +120,6 @@ public class PersistentActorExample {
         persistentActor.tell(new Cmd("foo"), null);
         persistentActor.tell(new Cmd("baz"), null);
         persistentActor.tell(new Cmd("bar"), null);
-        persistentActor.tell("snap", null);
         persistentActor.tell(new Cmd("buzz"), null);
         persistentActor.tell("print", null);
 

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

@@ -159,13 +159,21 @@ object PersistenceDocSpec {
     class MyPersistentActor extends PersistentActor {
       override def persistenceId = "my-stable-persistence-id"
 
+      def updateState(event: String): Unit = {}
+
       //#save-snapshot
       var state: Any = _
 
+      val snapShotInterval = 1000
       override def receiveCommand: Receive = {
-        case "snap"                                => saveSnapshot(state)
         case SaveSnapshotSuccess(metadata)         => // ...
         case SaveSnapshotFailure(metadata, reason) => // ...
+        case cmd: String =>
+          persist(s"evt-$cmd") { e =>
+            updateState(e)
+            if (lastSequenceNr % snapShotInterval == 0 && lastSequenceNr != 0)
+              saveSnapshot(state)
+          }
       }
       //#save-snapshot
 

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

@@ -29,14 +29,15 @@ class ExamplePersistentActor extends PersistentActor {
     case SnapshotOffer(_, snapshot: ExampleState) => state = snapshot
   }
 
+  val snapShotInterval = 1000
   val receiveCommand: Receive = {
     case Cmd(data) =>
-      persist(Evt(s"${data}-${numEvents}"))(updateState)
+      persist(Evt(s"${data}-${numEvents}")) { event =>
-      persist(Evt(s"${data}-${numEvents + 1}")) { event =>
         updateState(event)
         context.system.eventStream.publish(event)
+        if (lastSequenceNr % snapShotInterval == 0 && lastSequenceNr != 0)
+          saveSnapshot(state)
       }
-    case "snap"  => saveSnapshot(state)
     case "print" => println(state)
   }
 
@@ -51,7 +52,6 @@ object PersistentActorExample extends App {
   persistentActor ! Cmd("foo")
   persistentActor ! Cmd("baz")
   persistentActor ! Cmd("bar")
-  persistentActor ! "snap"
   persistentActor ! Cmd("buzz")
   persistentActor ! "print"