opendaylight/md-sal/sal-akka-raft/src/main/java/org/opendaylight/controller/cluster/raft/RaftActor.java

   1 /*
   2  * Copyright (c) 2014 Cisco Systems, Inc. and others.  All rights reserved.
   3  *
   4  * This program and the accompanying materials are made available under the
   5  * terms of the Eclipse Public License v1.0 which accompanies this distribution,
   6  * and is available at http://www.eclipse.org/legal/epl-v10.html
   7  */
   8
   9 package org.opendaylight.controller.cluster.raft;
  10
  11 import akka.actor.ActorRef;
  12 import akka.actor.ActorSelection;
  13 import akka.japi.Procedure;
  14 import akka.persistence.RecoveryCompleted;
  15 import akka.persistence.SaveSnapshotFailure;
  16 import akka.persistence.SaveSnapshotSuccess;
  17 import akka.persistence.SnapshotOffer;
  18 import akka.persistence.SnapshotSelectionCriteria;
  19 import com.google.common.annotations.VisibleForTesting;
  20 import com.google.common.base.Objects;
  21 import com.google.common.base.Optional;
  22 import com.google.common.base.Stopwatch;
  23 import com.google.common.collect.ImmutableMap;
  24 import com.google.common.collect.Lists;
  25 import java.io.Serializable;
  26 import java.util.Collection;
  27 import java.util.List;
  28 import java.util.Map;
  29 import java.util.concurrent.TimeUnit;
  30 import org.apache.commons.lang3.time.DurationFormatUtils;
  31 import org.opendaylight.controller.cluster.DataPersistenceProvider;
  32 import org.opendaylight.controller.cluster.DelegatingPersistentDataProvider;
  33 import org.opendaylight.controller.cluster.NonPersistentDataProvider;
  34 import org.opendaylight.controller.cluster.PersistentDataProvider;
  35 import org.opendaylight.controller.cluster.common.actor.AbstractUntypedPersistentActor;
  36 import org.opendaylight.controller.cluster.notifications.LeaderStateChanged;
  37 import org.opendaylight.controller.cluster.notifications.RoleChanged;
  38 import org.opendaylight.controller.cluster.raft.base.messages.ApplyJournalEntries;
  39 import org.opendaylight.controller.cluster.raft.base.messages.ApplyLogEntries;
  40 import org.opendaylight.controller.cluster.raft.base.messages.ApplySnapshot;
  41 import org.opendaylight.controller.cluster.raft.base.messages.ApplyState;
  42 import org.opendaylight.controller.cluster.raft.base.messages.CaptureSnapshot;
  43 import org.opendaylight.controller.cluster.raft.base.messages.CaptureSnapshotReply;
  44 import org.opendaylight.controller.cluster.raft.base.messages.Replicate;
  45 import org.opendaylight.controller.cluster.raft.behaviors.AbstractLeader;
  46 import org.opendaylight.controller.cluster.raft.behaviors.DelegatingRaftActorBehavior;
  47 import org.opendaylight.controller.cluster.raft.behaviors.Follower;
  48 import org.opendaylight.controller.cluster.raft.behaviors.RaftActorBehavior;
  49 import org.opendaylight.controller.cluster.raft.client.messages.FindLeader;
  50 import org.opendaylight.controller.cluster.raft.client.messages.FindLeaderReply;
  51 import org.opendaylight.controller.cluster.raft.client.messages.FollowerInfo;
  52 import org.opendaylight.controller.cluster.raft.client.messages.GetOnDemandRaftState;
  53 import org.opendaylight.controller.cluster.raft.client.messages.OnDemandRaftState;
  54 import org.opendaylight.controller.cluster.raft.protobuff.client.messages.Payload;
  55 import org.slf4j.Logger;
  56 import org.slf4j.LoggerFactory;
  57
  58 /**
  59  * RaftActor encapsulates a state machine that needs to be kept synchronized
  60  * in a cluster. It implements the RAFT algorithm as described in the paper
  61  * <a href='https://ramcloud.stanford.edu/wiki/download/attachments/11370504/raft.pdf'>
  62  * In Search of an Understandable Consensus Algorithm</a>
  63  * <p/>
  64  * RaftActor has 3 states and each state has a certain behavior associated
  65  * with it. A Raft actor can behave as,
  66  * <ul>
  67  * <li> A Leader </li>
  68  * <li> A Follower (or) </li>
  69  * <li> A Candidate </li>
  70  * </ul>
  71  * <p/>
  72  * <p/>
  73  * A RaftActor MUST be a Leader in order to accept requests from clients to
  74  * change the state of it's encapsulated state machine. Once a RaftActor becomes
  75  * a Leader it is also responsible for ensuring that all followers ultimately
  76  * have the same log and therefore the same state machine as itself.
  77  * <p/>
  78  * <p/>
  79  * The current behavior of a RaftActor determines how election for leadership
  80  * is initiated and how peer RaftActors react to request for votes.
  81  * <p/>
  82  * <p/>
  83  * Each RaftActor also needs to know the current election term. It uses this
  84  * information for a couple of things. One is to simply figure out who it
  85  * voted for in the last election. Another is to figure out if the message
  86  * it received to update it's state is stale.
  87  * <p/>
  88  * <p/>
  89  * The RaftActor uses akka-persistence to store it's replicated log.
  90  * Furthermore through it's behaviors a Raft Actor determines
  91  * <p/>
  92  * <ul>
  93  * <li> when a log entry should be persisted </li>
  94  * <li> when a log entry should be applied to the state machine (and) </li>
  95  * <li> when a snapshot should be saved </li>
  96  * </ul>
  97  */
  98 public abstract class RaftActor extends AbstractUntypedPersistentActor {
  99
 100     private static final long APPLY_STATE_DELAY_THRESHOLD_IN_NANOS = TimeUnit.MILLISECONDS.toNanos(50L); // 50 millis
 101
 102     private static final String COMMIT_SNAPSHOT = "commit_snapshot";
 103
 104     protected final Logger LOG = LoggerFactory.getLogger(getClass());
 105
 106     /**
 107      * The current state determines the current behavior of a RaftActor
 108      * A Raft Actor always starts off in the Follower State
 109      */
 110     private final DelegatingRaftActorBehavior currentBehavior = new DelegatingRaftActorBehavior();
 111
 112     /**
 113      * This context should NOT be passed directly to any other actor it is
 114      * only to be consumed by the RaftActorBehaviors
 115      */
 116     private final RaftActorContextImpl context;
 117
 118     private final DelegatingPersistentDataProvider delegatingPersistenceProvider = new DelegatingPersistentDataProvider(null);
 119
 120     private final Procedure<Void> createSnapshotProcedure = new CreateSnapshotProcedure();
 121
 122     private Stopwatch recoveryTimer;
 123
 124     private int currentRecoveryBatchCount;
 125
 126     private final BehaviorStateHolder reusableBehaviorStateHolder = new BehaviorStateHolder();
 127
 128     public RaftActor(String id, Map<String, String> peerAddresses) {
 129         this(id, peerAddresses, Optional.<ConfigParams>absent());
 130     }
 131
 132     public RaftActor(String id, Map<String, String> peerAddresses,
 133          Optional<ConfigParams> configParams) {
 134
 135         context = new RaftActorContextImpl(this.getSelf(),
 136             this.getContext(), id, new ElectionTermImpl(delegatingPersistenceProvider, id, LOG),
 137             -1, -1, peerAddresses,
 138             (configParams.isPresent() ? configParams.get(): new DefaultConfigParamsImpl()), LOG);
 139
 140         context.setReplicatedLog(ReplicatedLogImpl.newInstance(context, delegatingPersistenceProvider, currentBehavior));
 141     }
 142
 143     private void initRecoveryTimer() {
 144         if(recoveryTimer == null) {
 145             recoveryTimer = Stopwatch.createStarted();
 146         }
 147     }
 148
 149     @Override
 150     public void preStart() throws Exception {
 151         LOG.info("Starting recovery for {} with journal batch size {}", persistenceId(),
 152                 context.getConfigParams().getJournalRecoveryLogBatchSize());
 153
 154         super.preStart();
 155     }
 156
 157     @Override
 158     public void postStop() {
 159         if(currentBehavior != null) {
 160             try {
 161                 currentBehavior.close();
 162             } catch (Exception e) {
 163                 LOG.debug("{}: Error closing behavior {}", persistenceId(), currentBehavior.state());
 164             }
 165         }
 166
 167         super.postStop();
 168     }
 169
 170     @Override
 171     public void handleRecover(Object message) {
 172         if(persistence().isRecoveryApplicable()) {
 173             if (message instanceof SnapshotOffer) {
 174                 onRecoveredSnapshot((SnapshotOffer) message);
 175             } else if (message instanceof ReplicatedLogEntry) {
 176                 onRecoveredJournalLogEntry((ReplicatedLogEntry) message);
 177             } else if (message instanceof ApplyLogEntries) {
 178                 // Handle this message for backwards compatibility with pre-Lithium versions.
 179                 onRecoveredApplyLogEntries(((ApplyLogEntries) message).getToIndex());
 180             } else if (message instanceof ApplyJournalEntries) {
 181                 onRecoveredApplyLogEntries(((ApplyJournalEntries) message).getToIndex());
 182             } else if (message instanceof DeleteEntries) {
 183                 replicatedLog().removeFrom(((DeleteEntries) message).getFromIndex());
 184             } else if (message instanceof UpdateElectionTerm) {
 185                 context.getTermInformation().update(((UpdateElectionTerm) message).getCurrentTerm(),
 186                         ((UpdateElectionTerm) message).getVotedFor());
 187             } else if (message instanceof RecoveryCompleted) {
 188                 onRecoveryCompletedMessage();
 189             }
 190         } else {
 191             if (message instanceof RecoveryCompleted) {
 192                 // Delete all the messages from the akka journal so that we do not end up with consistency issues
 193                 // Note I am not using the dataPersistenceProvider and directly using the akka api here
 194                 deleteMessages(lastSequenceNr());
 195
 196                 // Delete all the akka snapshots as they will not be needed
 197                 deleteSnapshots(new SnapshotSelectionCriteria(scala.Long.MaxValue(), scala.Long.MaxValue()));
 198
 199                 onRecoveryComplete();
 200
 201                 initializeBehavior();
 202             }
 203         }
 204     }
 205
 206     private void onRecoveredSnapshot(SnapshotOffer offer) {
 207         if(LOG.isDebugEnabled()) {
 208             LOG.debug("{}: SnapshotOffer called..", persistenceId());
 209         }
 210
 211         initRecoveryTimer();
 212
 213         Snapshot snapshot = (Snapshot) offer.snapshot();
 214
 215         // Create a replicated log with the snapshot information
 216         // The replicated log can be used later on to retrieve this snapshot
 217         // when we need to install it on a peer
 218
 219         context.setReplicatedLog(ReplicatedLogImpl.newInstance(snapshot, context, delegatingPersistenceProvider,
 220                 currentBehavior));
 221         context.setLastApplied(snapshot.getLastAppliedIndex());
 222         context.setCommitIndex(snapshot.getLastAppliedIndex());
 223
 224         Stopwatch timer = Stopwatch.createStarted();
 225
 226         // Apply the snapshot to the actors state
 227         applyRecoverySnapshot(snapshot.getState());
 228
 229         timer.stop();
 230         LOG.info("Recovery snapshot applied for {} in {}: snapshotIndex={}, snapshotTerm={}, journal-size=" +
 231                 replicatedLog().size(), persistenceId(), timer.toString(),
 232                 replicatedLog().getSnapshotIndex(), replicatedLog().getSnapshotTerm());
 233     }
 234
 235     private void onRecoveredJournalLogEntry(ReplicatedLogEntry logEntry) {
 236         if(LOG.isDebugEnabled()) {
 237             LOG.debug("{}: Received ReplicatedLogEntry for recovery: {}", persistenceId(), logEntry.getIndex());
 238         }
 239
 240         replicatedLog().append(logEntry);
 241     }
 242
 243     private void onRecoveredApplyLogEntries(long toIndex) {
 244         if(LOG.isDebugEnabled()) {
 245             LOG.debug("{}: Received ApplyLogEntries for recovery, applying to state: {} to {}",
 246                     persistenceId(), context.getLastApplied() + 1, toIndex);
 247         }
 248
 249         for (long i = context.getLastApplied() + 1; i <= toIndex; i++) {
 250             batchRecoveredLogEntry(replicatedLog().get(i));
 251         }
 252
 253         context.setLastApplied(toIndex);
 254         context.setCommitIndex(toIndex);
 255     }
 256
 257     private void batchRecoveredLogEntry(ReplicatedLogEntry logEntry) {
 258         initRecoveryTimer();
 259
 260         int batchSize = context.getConfigParams().getJournalRecoveryLogBatchSize();
 261         if(currentRecoveryBatchCount == 0) {
 262             startLogRecoveryBatch(batchSize);
 263         }
 264
 265         appendRecoveredLogEntry(logEntry.getData());
 266
 267         if(++currentRecoveryBatchCount >= batchSize) {
 268             endCurrentLogRecoveryBatch();
 269         }
 270     }
 271
 272     private void endCurrentLogRecoveryBatch() {
 273         applyCurrentLogRecoveryBatch();
 274         currentRecoveryBatchCount = 0;
 275     }
 276
 277     private void onRecoveryCompletedMessage() {
 278         if(currentRecoveryBatchCount > 0) {
 279             endCurrentLogRecoveryBatch();
 280         }
 281
 282         onRecoveryComplete();
 283
 284         String recoveryTime = "";
 285         if(recoveryTimer != null) {
 286             recoveryTimer.stop();
 287             recoveryTime = " in " + recoveryTimer.toString();
 288             recoveryTimer = null;
 289         }
 290
 291         LOG.info(
 292             "Recovery completed" + recoveryTime + " - Switching actor to Follower - " +
 293                 "Persistence Id =  " + persistenceId() +
 294                 " Last index in log={}, snapshotIndex={}, snapshotTerm={}, " +
 295                 "journal-size={}",
 296             replicatedLog().lastIndex(), replicatedLog().getSnapshotIndex(),
 297             replicatedLog().getSnapshotTerm(), replicatedLog().size());
 298
 299         initializeBehavior();
 300     }
 301
 302     protected void initializeBehavior(){
 303         changeCurrentBehavior(new Follower(context));
 304     }
 305
 306     protected void changeCurrentBehavior(RaftActorBehavior newBehavior){
 307         reusableBehaviorStateHolder.init(getCurrentBehavior());
 308         setCurrentBehavior(newBehavior);
 309         handleBehaviorChange(reusableBehaviorStateHolder, getCurrentBehavior());
 310     }
 311
 312     @Override public void handleCommand(Object message) {
 313         if (message instanceof ApplyState){
 314             ApplyState applyState = (ApplyState) message;
 315
 316             long elapsedTime = (System.nanoTime() - applyState.getStartTime());
 317             if(elapsedTime >= APPLY_STATE_DELAY_THRESHOLD_IN_NANOS){
 318                 LOG.warn("ApplyState took more time than expected. Elapsed Time = {} ms ApplyState = {}",
 319                         TimeUnit.NANOSECONDS.toMillis(elapsedTime), applyState);
 320             }
 321
 322             if(LOG.isDebugEnabled()) {
 323                 LOG.debug("{}: Applying state for log index {} data {}",
 324                     persistenceId(), applyState.getReplicatedLogEntry().getIndex(),
 325                     applyState.getReplicatedLogEntry().getData());
 326             }
 327
 328             applyState(applyState.getClientActor(), applyState.getIdentifier(),
 329                 applyState.getReplicatedLogEntry().getData());
 330
 331         } else if (message instanceof ApplyJournalEntries){
 332             ApplyJournalEntries applyEntries = (ApplyJournalEntries) message;
 333             if(LOG.isDebugEnabled()) {
 334                 LOG.debug("{}: Persisting ApplyLogEntries with index={}", persistenceId(), applyEntries.getToIndex());
 335             }
 336
 337             persistence().persist(applyEntries, NoopProcedure.instance());
 338
 339         } else if(message instanceof ApplySnapshot ) {
 340             Snapshot snapshot = ((ApplySnapshot) message).getSnapshot();
 341
 342             if(LOG.isDebugEnabled()) {
 343                 LOG.debug("{}: ApplySnapshot called on Follower Actor " +
 344                         "snapshotIndex:{}, snapshotTerm:{}", persistenceId(), snapshot.getLastAppliedIndex(),
 345                     snapshot.getLastAppliedTerm()
 346                 );
 347             }
 348
 349             applySnapshot(snapshot.getState());
 350
 351             //clears the followers log, sets the snapshot index to ensure adjusted-index works
 352             context.setReplicatedLog(ReplicatedLogImpl.newInstance(snapshot, context, delegatingPersistenceProvider,
 353                     currentBehavior));
 354             context.setLastApplied(snapshot.getLastAppliedIndex());
 355
 356         } else if (message instanceof FindLeader) {
 357             getSender().tell(
 358                 new FindLeaderReply(getLeaderAddress()),
 359                 getSelf()
 360             );
 361
 362         } else if (message instanceof SaveSnapshotSuccess) {
 363             SaveSnapshotSuccess success = (SaveSnapshotSuccess) message;
 364             LOG.info("{}: SaveSnapshotSuccess received for snapshot", persistenceId());
 365
 366             long sequenceNumber = success.metadata().sequenceNr();
 367
 368             commitSnapshot(sequenceNumber);
 369
 370         } else if (message instanceof SaveSnapshotFailure) {
 371             SaveSnapshotFailure saveSnapshotFailure = (SaveSnapshotFailure) message;
 372
 373             LOG.error("{}: SaveSnapshotFailure received for snapshot Cause:",
 374                     persistenceId(), saveSnapshotFailure.cause());
 375
 376             context.getSnapshotManager().rollback();
 377
 378         } else if (message instanceof CaptureSnapshot) {
 379             LOG.debug("{}: CaptureSnapshot received by actor: {}", persistenceId(), message);
 380
 381             context.getSnapshotManager().create(createSnapshotProcedure);
 382
 383         } else if (message instanceof CaptureSnapshotReply) {
 384             handleCaptureSnapshotReply(((CaptureSnapshotReply) message).getSnapshot());
 385         } else if(message instanceof GetOnDemandRaftState) {
 386             onGetOnDemandRaftStats();
 387         } else if (message.equals(COMMIT_SNAPSHOT)) {
 388             commitSnapshot(-1);
 389         } else {
 390             reusableBehaviorStateHolder.init(getCurrentBehavior());
 391
 392             setCurrentBehavior(currentBehavior.handleMessage(getSender(), message));
 393
 394             handleBehaviorChange(reusableBehaviorStateHolder, getCurrentBehavior());
 395         }
 396     }
 397
 398     private void onGetOnDemandRaftStats() {
 399         // Debugging message to retrieve raft stats.
 400
 401         OnDemandRaftState.Builder builder = OnDemandRaftState.builder()
 402                 .commitIndex(context.getCommitIndex())
 403                 .currentTerm(context.getTermInformation().getCurrentTerm())
 404                 .inMemoryJournalDataSize(replicatedLog().dataSize())
 405                 .inMemoryJournalLogSize(replicatedLog().size())
 406                 .isSnapshotCaptureInitiated(context.getSnapshotManager().isCapturing())
 407                 .lastApplied(context.getLastApplied())
 408                 .lastIndex(replicatedLog().lastIndex())
 409                 .lastTerm(replicatedLog().lastTerm())
 410                 .leader(getLeaderId())
 411                 .raftState(currentBehavior.state().toString())
 412                 .replicatedToAllIndex(currentBehavior.getReplicatedToAllIndex())
 413                 .snapshotIndex(replicatedLog().getSnapshotIndex())
 414                 .snapshotTerm(replicatedLog().getSnapshotTerm())
 415                 .votedFor(context.getTermInformation().getVotedFor())
 416                 .peerAddresses(ImmutableMap.copyOf(context.getPeerAddresses()));
 417
 418         ReplicatedLogEntry lastLogEntry = getLastLogEntry();
 419         if (lastLogEntry != null) {
 420             builder.lastLogIndex(lastLogEntry.getIndex());
 421             builder.lastLogTerm(lastLogEntry.getTerm());
 422         }
 423
 424         if(getCurrentBehavior() instanceof AbstractLeader) {
 425             AbstractLeader leader = (AbstractLeader)getCurrentBehavior();
 426             Collection<String> followerIds = leader.getFollowerIds();
 427             List<FollowerInfo> followerInfoList = Lists.newArrayListWithCapacity(followerIds.size());
 428             for(String id: followerIds) {
 429                 final FollowerLogInformation info = leader.getFollower(id);
 430                 followerInfoList.add(new FollowerInfo(id, info.getNextIndex(), info.getMatchIndex(),
 431                         info.isFollowerActive(), DurationFormatUtils.formatDurationHMS(info.timeSinceLastActivity())));
 432             }
 433
 434             builder.followerInfoList(followerInfoList);
 435         }
 436
 437         sender().tell(builder.build(), self());
 438
 439     }
 440
 441     private void handleBehaviorChange(BehaviorStateHolder oldBehaviorState, RaftActorBehavior currentBehavior) {
 442         RaftActorBehavior oldBehavior = oldBehaviorState.getBehavior();
 443
 444         if (oldBehavior != currentBehavior){
 445             onStateChanged();
 446         }
 447
 448         String oldBehaviorLeaderId = oldBehavior == null ? null : oldBehaviorState.getLeaderId();
 449         String oldBehaviorStateName = oldBehavior == null ? null : oldBehavior.state().name();
 450
 451         // it can happen that the state has not changed but the leader has changed.
 452         Optional<ActorRef> roleChangeNotifier = getRoleChangeNotifier();
 453         if(!Objects.equal(oldBehaviorLeaderId, currentBehavior.getLeaderId())) {
 454             if(roleChangeNotifier.isPresent()) {
 455                 roleChangeNotifier.get().tell(new LeaderStateChanged(getId(), currentBehavior.getLeaderId()), getSelf());
 456             }
 457
 458             onLeaderChanged(oldBehaviorLeaderId, currentBehavior.getLeaderId());
 459         }
 460
 461         if (roleChangeNotifier.isPresent() &&
 462                 (oldBehavior == null || (oldBehavior.state() != currentBehavior.state()))) {
 463             roleChangeNotifier.get().tell(new RoleChanged(getId(), oldBehaviorStateName ,
 464                     currentBehavior.state().name()), getSelf());
 465         }
 466     }
 467
 468     /**
 469      * When a derived RaftActor needs to persist something it must call
 470      * persistData.
 471      *
 472      * @param clientActor
 473      * @param identifier
 474      * @param data
 475      */
 476     protected void persistData(final ActorRef clientActor, final String identifier,
 477         final Payload data) {
 478
 479         ReplicatedLogEntry replicatedLogEntry = new ReplicatedLogImplEntry(
 480             context.getReplicatedLog().lastIndex() + 1,
 481             context.getTermInformation().getCurrentTerm(), data);
 482
 483         if(LOG.isDebugEnabled()) {
 484             LOG.debug("{}: Persist data {}", persistenceId(), replicatedLogEntry);
 485         }
 486
 487         final RaftActorContext raftContext = getRaftActorContext();
 488
 489         replicatedLog().appendAndPersist(replicatedLogEntry, new Procedure<ReplicatedLogEntry>() {
 490             @Override
 491             public void apply(ReplicatedLogEntry replicatedLogEntry) throws Exception {
 492                 if(!hasFollowers()){
 493                     // Increment the Commit Index and the Last Applied values
 494                     raftContext.setCommitIndex(replicatedLogEntry.getIndex());
 495                     raftContext.setLastApplied(replicatedLogEntry.getIndex());
 496
 497                     // Apply the state immediately
 498                     applyState(clientActor, identifier, data);
 499
 500                     // Send a ApplyJournalEntries message so that we write the fact that we applied
 501                     // the state to durable storage
 502                     self().tell(new ApplyJournalEntries(replicatedLogEntry.getIndex()), self());
 503
 504                     context.getSnapshotManager().trimLog(context.getLastApplied(), currentBehavior);
 505
 506                 } else if (clientActor != null) {
 507                     // Send message for replication
 508                     currentBehavior.handleMessage(getSelf(),
 509                             new Replicate(clientActor, identifier, replicatedLogEntry));
 510                 }
 511             }
 512         });
 513     }
 514
 515     private ReplicatedLog replicatedLog() {
 516         return context.getReplicatedLog();
 517     }
 518
 519     protected String getId() {
 520         return context.getId();
 521     }
 522
 523     @VisibleForTesting
 524     void setCurrentBehavior(RaftActorBehavior behavior) {
 525         currentBehavior.setDelegate(behavior);
 526     }
 527
 528     protected RaftActorBehavior getCurrentBehavior() {
 529         return currentBehavior.getDelegate();
 530     }
 531
 532     /**
 533      * Derived actors can call the isLeader method to check if the current
 534      * RaftActor is the Leader or not
 535      *
 536      * @return true it this RaftActor is a Leader false otherwise
 537      */
 538     protected boolean isLeader() {
 539         return context.getId().equals(currentBehavior.getLeaderId());
 540     }
 541
 542     /**
 543      * Derived actor can call getLeader if they need a reference to the Leader.
 544      * This would be useful for example in forwarding a request to an actor
 545      * which is the leader
 546      *
 547      * @return A reference to the leader if known, null otherwise
 548      */
 549     protected ActorSelection getLeader(){
 550         String leaderAddress = getLeaderAddress();
 551
 552         if(leaderAddress == null){
 553             return null;
 554         }
 555
 556         return context.actorSelection(leaderAddress);
 557     }
 558
 559     /**
 560      *
 561      * @return the current leader's id
 562      */
 563     protected String getLeaderId(){
 564         return currentBehavior.getLeaderId();
 565     }
 566
 567     protected RaftState getRaftState() {
 568         return currentBehavior.state();
 569     }
 570
 571     protected ReplicatedLogEntry getLastLogEntry() {
 572         return replicatedLog().last();
 573     }
 574
 575     protected Long getCurrentTerm(){
 576         return context.getTermInformation().getCurrentTerm();
 577     }
 578
 579     protected Long getCommitIndex(){
 580         return context.getCommitIndex();
 581     }
 582
 583     protected Long getLastApplied(){
 584         return context.getLastApplied();
 585     }
 586
 587     protected RaftActorContext getRaftActorContext() {
 588         return context;
 589     }
 590
 591     protected void updateConfigParams(ConfigParams configParams) {
 592         context.setConfigParams(configParams);
 593     }
 594
 595     public final DataPersistenceProvider persistence() {
 596         return delegatingPersistenceProvider.getDelegate();
 597     }
 598
 599     public void setPersistence(DataPersistenceProvider provider) {
 600         delegatingPersistenceProvider.setDelegate(provider);
 601     }
 602
 603     protected void setPersistence(boolean persistent) {
 604         if(persistent) {
 605             setPersistence(new PersistentDataProvider(this));
 606         } else {
 607             setPersistence(new NonPersistentDataProvider() {
 608                 /**
 609                  * The way snapshotting works is,
 610                  * <ol>
 611                  * <li> RaftActor calls createSnapshot on the Shard
 612                  * <li> Shard sends a CaptureSnapshotReply and RaftActor then calls saveSnapshot
 613                  * <li> When saveSnapshot is invoked on the akka-persistence API it uses the SnapshotStore to save
 614                  * the snapshot. The SnapshotStore sends SaveSnapshotSuccess or SaveSnapshotFailure. When the
 615                  * RaftActor gets SaveSnapshot success it commits the snapshot to the in-memory journal. This
 616                  * commitSnapshot is mimicking what is done in SaveSnapshotSuccess.
 617                  * </ol>
 618                  */
 619                 @Override
 620                 public void saveSnapshot(Object o) {
 621                     // Make saving Snapshot successful
 622                     // Committing the snapshot here would end up calling commit in the creating state which would
 623                     // be a state violation. That's why now we send a message to commit the snapshot.
 624                     self().tell(COMMIT_SNAPSHOT, self());
 625                 }
 626             });
 627         }
 628     }
 629
 630     /**
 631      * setPeerAddress sets the address of a known peer at a later time.
 632      * <p>
 633      * This is to account for situations where a we know that a peer
 634      * exists but we do not know an address up-front. This may also be used in
 635      * situations where a known peer starts off in a different location and we
 636      * need to change it's address
 637      * <p>
 638      * Note that if the peerId does not match the list of peers passed to
 639      * this actor during construction an IllegalStateException will be thrown.
 640      *
 641      * @param peerId
 642      * @param peerAddress
 643      */
 644     protected void setPeerAddress(String peerId, String peerAddress){
 645         context.setPeerAddress(peerId, peerAddress);
 646     }
 647
 648     protected void commitSnapshot(long sequenceNumber) {
 649         context.getSnapshotManager().commit(persistence(), sequenceNumber);
 650     }
 651
 652     /**
 653      * The applyState method will be called by the RaftActor when some data
 654      * needs to be applied to the actor's state
 655      *
 656      * @param clientActor A reference to the client who sent this message. This
 657      *                    is the same reference that was passed to persistData
 658      *                    by the derived actor. clientActor may be null when
 659      *                    the RaftActor is behaving as a follower or during
 660      *                    recovery.
 661      * @param identifier  The identifier of the persisted data. This is also
 662      *                    the same identifier that was passed to persistData by
 663      *                    the derived actor. identifier may be null when
 664      *                    the RaftActor is behaving as a follower or during
 665      *                    recovery
 666      * @param data        A piece of data that was persisted by the persistData call.
 667      *                    This should NEVER be null.
 668      */
 669     protected abstract void applyState(ActorRef clientActor, String identifier,
 670         Object data);
 671
 672     /**
 673      * This method is called during recovery at the start of a batch of state entries. Derived
 674      * classes should perform any initialization needed to start a batch.
 675      */
 676     protected abstract void startLogRecoveryBatch(int maxBatchSize);
 677
 678     /**
 679      * This method is called during recovery to append state data to the current batch. This method
 680      * is called 1 or more times after {@link #startLogRecoveryBatch}.
 681      *
 682      * @param data the state data
 683      */
 684     protected abstract void appendRecoveredLogEntry(Payload data);
 685
 686     /**
 687      * This method is called during recovery to reconstruct the state of the actor.
 688      *
 689      * @param snapshotBytes A snapshot of the state of the actor
 690      */
 691     protected abstract void applyRecoverySnapshot(byte[] snapshotBytes);
 692
 693     /**
 694      * This method is called during recovery at the end of a batch to apply the current batched
 695      * log entries. This method is called after {@link #appendRecoveredLogEntry}.
 696      */
 697     protected abstract void applyCurrentLogRecoveryBatch();
 698
 699     /**
 700      * This method is called when recovery is complete.
 701      */
 702     protected abstract void onRecoveryComplete();
 703
 704     /**
 705      * This method will be called by the RaftActor when a snapshot needs to be
 706      * created. The derived actor should respond with its current state.
 707      * <p/>
 708      * During recovery the state that is returned by the derived actor will
 709      * be passed back to it by calling the applySnapshot  method
 710      *
 711      * @return The current state of the actor
 712      */
 713     protected abstract void createSnapshot();
 714
 715     /**
 716      * This method can be called at any other point during normal
 717      * operations when the derived actor is out of sync with it's peers
 718      * and the only way to bring it in sync is by applying a snapshot
 719      *
 720      * @param snapshotBytes A snapshot of the state of the actor
 721      */
 722     protected abstract void applySnapshot(byte[] snapshotBytes);
 723
 724     /**
 725      * This method will be called by the RaftActor when the state of the
 726      * RaftActor changes. The derived actor can then use methods like
 727      * isLeader or getLeader to do something useful
 728      */
 729     protected abstract void onStateChanged();
 730
 731     /**
 732      * Notifier Actor for this RaftActor to notify when a role change happens
 733      * @return ActorRef - ActorRef of the notifier or Optional.absent if none.
 734      */
 735     protected abstract Optional<ActorRef> getRoleChangeNotifier();
 736
 737     protected void onLeaderChanged(String oldLeader, String newLeader){};
 738
 739     private String getLeaderAddress(){
 740         if(isLeader()){
 741             return getSelf().path().toString();
 742         }
 743         String leaderId = currentBehavior.getLeaderId();
 744         if (leaderId == null) {
 745             return null;
 746         }
 747         String peerAddress = context.getPeerAddress(leaderId);
 748         if(LOG.isDebugEnabled()) {
 749             LOG.debug("{}: getLeaderAddress leaderId = {} peerAddress = {}",
 750                     persistenceId(), leaderId, peerAddress);
 751         }
 752
 753         return peerAddress;
 754     }
 755
 756     private void handleCaptureSnapshotReply(byte[] snapshotBytes) {
 757         LOG.debug("{}: CaptureSnapshotReply received by actor: snapshot size {}", persistenceId(), snapshotBytes.length);
 758
 759         context.getSnapshotManager().persist(persistence(), snapshotBytes, currentBehavior, context.getTotalMemory());
 760     }
 761
 762     protected boolean hasFollowers(){
 763         return getRaftActorContext().hasFollowers();
 764     }
 765
 766     static class DeleteEntries implements Serializable {
 767         private static final long serialVersionUID = 1L;
 768         private final int fromIndex;
 769
 770         public DeleteEntries(int fromIndex) {
 771             this.fromIndex = fromIndex;
 772         }
 773
 774         public int getFromIndex() {
 775             return fromIndex;
 776         }
 777     }
 778
 779     static class UpdateElectionTerm implements Serializable {
 780         private static final long serialVersionUID = 1L;
 781         private final long currentTerm;
 782         private final String votedFor;
 783
 784         public UpdateElectionTerm(long currentTerm, String votedFor) {
 785             this.currentTerm = currentTerm;
 786             this.votedFor = votedFor;
 787         }
 788
 789         public long getCurrentTerm() {
 790             return currentTerm;
 791         }
 792
 793         public String getVotedFor() {
 794             return votedFor;
 795         }
 796     }
 797
 798     private class CreateSnapshotProcedure implements Procedure<Void> {
 799
 800         @Override
 801         public void apply(Void aVoid) throws Exception {
 802             createSnapshot();
 803         }
 804     }
 805
 806     private static class BehaviorStateHolder {
 807         private RaftActorBehavior behavior;
 808         private String leaderId;
 809
 810         void init(RaftActorBehavior behavior) {
 811             this.behavior = behavior;
 812             this.leaderId = behavior != null ? behavior.getLeaderId() : null;
 813         }
 814
 815         RaftActorBehavior getBehavior() {
 816             return behavior;
 817         }
 818
 819         String getLeaderId() {
 820             return leaderId;
 821         }
 822     }
 823 }