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.event.Logging;
  14 import akka.event.LoggingAdapter;
  15 import akka.japi.Procedure;
  16 import akka.persistence.RecoveryCompleted;
  17 import akka.persistence.SaveSnapshotFailure;
  18 import akka.persistence.SaveSnapshotSuccess;
  19 import akka.persistence.SnapshotOffer;
  20 import akka.persistence.SnapshotSelectionCriteria;
  21 import akka.persistence.UntypedPersistentActor;
  22 import com.google.common.base.Optional;
  23 import com.google.common.base.Stopwatch;
  24 import com.google.protobuf.ByteString;
  25 import org.opendaylight.controller.cluster.raft.base.messages.ApplyLogEntries;
  26 import org.opendaylight.controller.cluster.raft.base.messages.ApplySnapshot;
  27 import org.opendaylight.controller.cluster.raft.base.messages.ApplyState;
  28 import org.opendaylight.controller.cluster.raft.base.messages.CaptureSnapshot;
  29 import org.opendaylight.controller.cluster.raft.base.messages.CaptureSnapshotReply;
  30 import org.opendaylight.controller.cluster.raft.base.messages.Replicate;
  31 import org.opendaylight.controller.cluster.raft.base.messages.SendHeartBeat;
  32 import org.opendaylight.controller.cluster.raft.behaviors.Candidate;
  33 import org.opendaylight.controller.cluster.raft.behaviors.Follower;
  34 import org.opendaylight.controller.cluster.raft.behaviors.Leader;
  35 import org.opendaylight.controller.cluster.raft.behaviors.RaftActorBehavior;
  36 import org.opendaylight.controller.cluster.raft.client.messages.AddRaftPeer;
  37 import org.opendaylight.controller.cluster.raft.client.messages.FindLeader;
  38 import org.opendaylight.controller.cluster.raft.client.messages.FindLeaderReply;
  39 import org.opendaylight.controller.cluster.raft.client.messages.RemoveRaftPeer;
  40 import org.opendaylight.controller.cluster.raft.messages.AppendEntriesReply;
  41 import org.opendaylight.controller.cluster.raft.protobuff.client.messages.Payload;
  42 import org.opendaylight.controller.protobuff.messages.cluster.raft.AppendEntriesMessages;
  43 import java.io.Serializable;
  44 import java.util.Map;
  45
  46 /**
  47  * RaftActor encapsulates a state machine that needs to be kept synchronized
  48  * in a cluster. It implements the RAFT algorithm as described in the paper
  49  * <a href='https://ramcloud.stanford.edu/wiki/download/attachments/11370504/raft.pdf'>
  50  * In Search of an Understandable Consensus Algorithm</a>
  51  * <p/>
  52  * RaftActor has 3 states and each state has a certain behavior associated
  53  * with it. A Raft actor can behave as,
  54  * <ul>
  55  * <li> A Leader </li>
  56  * <li> A Follower (or) </li>
  57  * <li> A Candidate </li>
  58  * </ul>
  59  * <p/>
  60  * <p/>
  61  * A RaftActor MUST be a Leader in order to accept requests from clients to
  62  * change the state of it's encapsulated state machine. Once a RaftActor becomes
  63  * a Leader it is also responsible for ensuring that all followers ultimately
  64  * have the same log and therefore the same state machine as itself.
  65  * <p/>
  66  * <p/>
  67  * The current behavior of a RaftActor determines how election for leadership
  68  * is initiated and how peer RaftActors react to request for votes.
  69  * <p/>
  70  * <p/>
  71  * Each RaftActor also needs to know the current election term. It uses this
  72  * information for a couple of things. One is to simply figure out who it
  73  * voted for in the last election. Another is to figure out if the message
  74  * it received to update it's state is stale.
  75  * <p/>
  76  * <p/>
  77  * The RaftActor uses akka-persistence to store it's replicated log.
  78  * Furthermore through it's behaviors a Raft Actor determines
  79  * <p/>
  80  * <ul>
  81  * <li> when a log entry should be persisted </li>
  82  * <li> when a log entry should be applied to the state machine (and) </li>
  83  * <li> when a snapshot should be saved </li>
  84  * </ul>
  85  */
  86 public abstract class RaftActor extends UntypedPersistentActor {
  87     protected final LoggingAdapter LOG =
  88         Logging.getLogger(getContext().system(), this);
  89
  90     /**
  91      * The current state determines the current behavior of a RaftActor
  92      * A Raft Actor always starts off in the Follower State
  93      */
  94     private RaftActorBehavior currentBehavior;
  95
  96     /**
  97      * This context should NOT be passed directly to any other actor it is
  98      * only to be consumed by the RaftActorBehaviors
  99      */
 100     private final RaftActorContext context;
 101
 102     /**
 103      * The in-memory journal
 104      */
 105     private ReplicatedLogImpl replicatedLog = new ReplicatedLogImpl();
 106
 107     private CaptureSnapshot captureSnapshot = null;
 108
 109     private volatile boolean hasSnapshotCaptureInitiated = false;
 110
 111     private Stopwatch recoveryTimer;
 112
 113     private int currentRecoveryBatchCount;
 114
 115     public RaftActor(String id, Map<String, String> peerAddresses) {
 116         this(id, peerAddresses, Optional.<ConfigParams>absent());
 117     }
 118
 119     public RaftActor(String id, Map<String, String> peerAddresses,
 120          Optional<ConfigParams> configParams) {
 121
 122         context = new RaftActorContextImpl(this.getSelf(),
 123             this.getContext(), id, new ElectionTermImpl(),
 124             -1, -1, replicatedLog, peerAddresses,
 125             (configParams.isPresent() ? configParams.get(): new DefaultConfigParamsImpl()),
 126             LOG);
 127     }
 128
 129     private void initRecoveryTimer() {
 130         if(recoveryTimer == null) {
 131             recoveryTimer = new Stopwatch();
 132             recoveryTimer.start();
 133         }
 134     }
 135
 136     @Override
 137     public void preStart() throws Exception {
 138         LOG.info("Starting recovery for {} with journal batch size {}", persistenceId(),
 139                 context.getConfigParams().getJournalRecoveryLogBatchSize());
 140         super.preStart();
 141     }
 142
 143     @Override
 144     public void onReceiveRecover(Object message) {
 145         if (message instanceof SnapshotOffer) {
 146             onRecoveredSnapshot((SnapshotOffer)message);
 147         } else if (message instanceof ReplicatedLogEntry) {
 148             onRecoveredJournalLogEntry((ReplicatedLogEntry)message);
 149         } else if (message instanceof ApplyLogEntries) {
 150             onRecoveredApplyLogEntries((ApplyLogEntries)message);
 151         } else if (message instanceof DeleteEntries) {
 152             replicatedLog.removeFrom(((DeleteEntries) message).getFromIndex());
 153         } else if (message instanceof UpdateElectionTerm) {
 154             context.getTermInformation().update(((UpdateElectionTerm) message).getCurrentTerm(),
 155                     ((UpdateElectionTerm) message).getVotedFor());
 156         } else if (message instanceof RecoveryCompleted) {
 157             onRecoveryCompletedMessage();
 158         }
 159     }
 160
 161     private void onRecoveredSnapshot(SnapshotOffer offer) {
 162         LOG.debug("SnapshotOffer called..");
 163
 164         initRecoveryTimer();
 165
 166         Snapshot snapshot = (Snapshot) offer.snapshot();
 167
 168         // Create a replicated log with the snapshot information
 169         // The replicated log can be used later on to retrieve this snapshot
 170         // when we need to install it on a peer
 171         replicatedLog = new ReplicatedLogImpl(snapshot);
 172
 173         context.setReplicatedLog(replicatedLog);
 174         context.setLastApplied(snapshot.getLastAppliedIndex());
 175         context.setCommitIndex(snapshot.getLastAppliedIndex());
 176
 177         Stopwatch timer = new Stopwatch();
 178         timer.start();
 179
 180         // Apply the snapshot to the actors state
 181         applyRecoverySnapshot(ByteString.copyFrom(snapshot.getState()));
 182
 183         timer.stop();
 184         LOG.info("Recovery snapshot applied for {} in {}: snapshotIndex={}, snapshotTerm={}, journal-size=" +
 185                 replicatedLog.size(), persistenceId(), timer.toString(),
 186                 replicatedLog.snapshotIndex, replicatedLog.snapshotTerm);
 187     }
 188
 189     private void onRecoveredJournalLogEntry(ReplicatedLogEntry logEntry) {
 190         if(LOG.isDebugEnabled()) {
 191             LOG.debug("Received ReplicatedLogEntry for recovery: {}", logEntry.getIndex());
 192         }
 193
 194         replicatedLog.append(logEntry);
 195     }
 196
 197     private void onRecoveredApplyLogEntries(ApplyLogEntries ale) {
 198         if(LOG.isDebugEnabled()) {
 199             LOG.debug("Received ApplyLogEntries for recovery, applying to state: {} to {}",
 200                     context.getLastApplied() + 1, ale.getToIndex());
 201         }
 202
 203         for (long i = context.getLastApplied() + 1; i <= ale.getToIndex(); i++) {
 204             batchRecoveredLogEntry(replicatedLog.get(i));
 205         }
 206
 207         context.setLastApplied(ale.getToIndex());
 208         context.setCommitIndex(ale.getToIndex());
 209     }
 210
 211     private void batchRecoveredLogEntry(ReplicatedLogEntry logEntry) {
 212         initRecoveryTimer();
 213
 214         int batchSize = context.getConfigParams().getJournalRecoveryLogBatchSize();
 215         if(currentRecoveryBatchCount == 0) {
 216             startLogRecoveryBatch(batchSize);
 217         }
 218
 219         appendRecoveredLogEntry(logEntry.getData());
 220
 221         if(++currentRecoveryBatchCount >= batchSize) {
 222             endCurrentLogRecoveryBatch();
 223         }
 224     }
 225
 226     private void endCurrentLogRecoveryBatch() {
 227         applyCurrentLogRecoveryBatch();
 228         currentRecoveryBatchCount = 0;
 229     }
 230
 231     private void onRecoveryCompletedMessage() {
 232         if(currentRecoveryBatchCount > 0) {
 233             endCurrentLogRecoveryBatch();
 234         }
 235
 236         onRecoveryComplete();
 237
 238         String recoveryTime = "";
 239         if(recoveryTimer != null) {
 240             recoveryTimer.stop();
 241             recoveryTime = " in " + recoveryTimer.toString();
 242             recoveryTimer = null;
 243         }
 244
 245         LOG.info(
 246             "Recovery completed" + recoveryTime + " - Switching actor to Follower - " +
 247                 "Persistence Id =  " + persistenceId() +
 248                 " Last index in log={}, snapshotIndex={}, snapshotTerm={}, " +
 249                 "journal-size={}",
 250             replicatedLog.lastIndex(), replicatedLog.snapshotIndex,
 251             replicatedLog.snapshotTerm, replicatedLog.size());
 252
 253         currentBehavior = switchBehavior(RaftState.Follower);
 254         onStateChanged();
 255     }
 256
 257     @Override public void onReceiveCommand(Object message) {
 258         if (message instanceof ApplyState){
 259             ApplyState applyState = (ApplyState) message;
 260
 261             if(LOG.isDebugEnabled()) {
 262                 LOG.debug("Applying state for log index {} data {}",
 263                     applyState.getReplicatedLogEntry().getIndex(),
 264                     applyState.getReplicatedLogEntry().getData());
 265             }
 266
 267             applyState(applyState.getClientActor(), applyState.getIdentifier(),
 268                 applyState.getReplicatedLogEntry().getData());
 269
 270         } else if (message instanceof ApplyLogEntries){
 271             ApplyLogEntries ale = (ApplyLogEntries) message;
 272             if(LOG.isDebugEnabled()) {
 273                 LOG.debug("Persisting ApplyLogEntries with index={}", ale.getToIndex());
 274             }
 275             persist(new ApplyLogEntries(ale.getToIndex()), new Procedure<ApplyLogEntries>() {
 276                 @Override
 277                 public void apply(ApplyLogEntries param) throws Exception {
 278                 }
 279             });
 280
 281         } else if(message instanceof ApplySnapshot ) {
 282             Snapshot snapshot = ((ApplySnapshot) message).getSnapshot();
 283
 284             if(LOG.isDebugEnabled()) {
 285                 LOG.debug("ApplySnapshot called on Follower Actor " +
 286                         "snapshotIndex:{}, snapshotTerm:{}", snapshot.getLastAppliedIndex(),
 287                     snapshot.getLastAppliedTerm()
 288                 );
 289             }
 290             applySnapshot(ByteString.copyFrom(snapshot.getState()));
 291
 292             //clears the followers log, sets the snapshot index to ensure adjusted-index works
 293             replicatedLog = new ReplicatedLogImpl(snapshot);
 294             context.setReplicatedLog(replicatedLog);
 295             context.setLastApplied(snapshot.getLastAppliedIndex());
 296
 297         } else if (message instanceof FindLeader) {
 298             getSender().tell(
 299                 new FindLeaderReply(getLeaderAddress()),
 300                 getSelf()
 301             );
 302
 303         } else if (message instanceof SaveSnapshotSuccess) {
 304             SaveSnapshotSuccess success = (SaveSnapshotSuccess) message;
 305             LOG.info("SaveSnapshotSuccess received for snapshot");
 306
 307             context.getReplicatedLog().snapshotCommit();
 308
 309             // TODO: Not sure if we want to be this aggressive with trimming stuff
 310             trimPersistentData(success.metadata().sequenceNr());
 311
 312         } else if (message instanceof SaveSnapshotFailure) {
 313             SaveSnapshotFailure saveSnapshotFailure = (SaveSnapshotFailure) message;
 314
 315             LOG.info("saveSnapshotFailure.metadata():{}", saveSnapshotFailure.metadata().toString());
 316             LOG.error(saveSnapshotFailure.cause(), "SaveSnapshotFailure received for snapshot Cause:");
 317
 318             context.getReplicatedLog().snapshotRollback();
 319
 320             LOG.info("Replicated Log rollbacked. Snapshot will be attempted in the next cycle." +
 321                 "snapshotIndex:{}, snapshotTerm:{}, log-size:{}",
 322                 context.getReplicatedLog().getSnapshotIndex(),
 323                 context.getReplicatedLog().getSnapshotTerm(),
 324                 context.getReplicatedLog().size());
 325
 326         } else if (message instanceof AddRaftPeer){
 327
 328             // FIXME : Do not add raft peers like this.
 329             // When adding a new Peer we have to ensure that the a majority of
 330             // the peers know about the new Peer. Doing it this way may cause
 331             // a situation where multiple Leaders may emerge
 332             AddRaftPeer arp = (AddRaftPeer)message;
 333            context.addToPeers(arp.getName(), arp.getAddress());
 334
 335         } else if (message instanceof RemoveRaftPeer){
 336
 337             RemoveRaftPeer rrp = (RemoveRaftPeer)message;
 338             context.removePeer(rrp.getName());
 339
 340         } else if (message instanceof CaptureSnapshot) {
 341             LOG.info("CaptureSnapshot received by actor");
 342             CaptureSnapshot cs = (CaptureSnapshot)message;
 343             captureSnapshot = cs;
 344             createSnapshot();
 345
 346         } else if (message instanceof CaptureSnapshotReply){
 347             LOG.info("CaptureSnapshotReply received by actor");
 348             CaptureSnapshotReply csr = (CaptureSnapshotReply) message;
 349
 350             ByteString stateInBytes = csr.getSnapshot();
 351             LOG.info("CaptureSnapshotReply stateInBytes size:{}", stateInBytes.size());
 352             handleCaptureSnapshotReply(stateInBytes);
 353
 354         } else {
 355             if (!(message instanceof AppendEntriesMessages.AppendEntries)
 356                 && !(message instanceof AppendEntriesReply) && !(message instanceof SendHeartBeat)) {
 357                 if(LOG.isDebugEnabled()) {
 358                     LOG.debug("onReceiveCommand: message:" + message.getClass());
 359                 }
 360             }
 361
 362             RaftState state =
 363                 currentBehavior.handleMessage(getSender(), message);
 364             RaftActorBehavior oldBehavior = currentBehavior;
 365             currentBehavior = switchBehavior(state);
 366             if(oldBehavior != currentBehavior){
 367                 onStateChanged();
 368             }
 369
 370             onLeaderChanged(oldBehavior.getLeaderId(), currentBehavior.getLeaderId());
 371         }
 372     }
 373
 374     public java.util.Set<String> getPeers() {
 375         return context.getPeerAddresses().keySet();
 376     }
 377
 378     protected String getReplicatedLogState() {
 379         return "snapshotIndex=" + context.getReplicatedLog().getSnapshotIndex()
 380             + ", snapshotTerm=" + context.getReplicatedLog().getSnapshotTerm()
 381             + ", im-mem journal size=" + context.getReplicatedLog().size();
 382     }
 383
 384
 385     /**
 386      * When a derived RaftActor needs to persist something it must call
 387      * persistData.
 388      *
 389      * @param clientActor
 390      * @param identifier
 391      * @param data
 392      */
 393     protected void persistData(ActorRef clientActor, String identifier,
 394         Payload data) {
 395
 396         ReplicatedLogEntry replicatedLogEntry = new ReplicatedLogImplEntry(
 397             context.getReplicatedLog().lastIndex() + 1,
 398             context.getTermInformation().getCurrentTerm(), data);
 399
 400         if(LOG.isDebugEnabled()) {
 401             LOG.debug("Persist data {}", replicatedLogEntry);
 402         }
 403
 404         replicatedLog
 405             .appendAndPersist(clientActor, identifier, replicatedLogEntry);
 406     }
 407
 408     protected String getId() {
 409         return context.getId();
 410     }
 411
 412     /**
 413      * Derived actors can call the isLeader method to check if the current
 414      * RaftActor is the Leader or not
 415      *
 416      * @return true it this RaftActor is a Leader false otherwise
 417      */
 418     protected boolean isLeader() {
 419         return context.getId().equals(currentBehavior.getLeaderId());
 420     }
 421
 422     /**
 423      * Derived actor can call getLeader if they need a reference to the Leader.
 424      * This would be useful for example in forwarding a request to an actor
 425      * which is the leader
 426      *
 427      * @return A reference to the leader if known, null otherwise
 428      */
 429     protected ActorSelection getLeader(){
 430         String leaderAddress = getLeaderAddress();
 431
 432         if(leaderAddress == null){
 433             return null;
 434         }
 435
 436         return context.actorSelection(leaderAddress);
 437     }
 438
 439     /**
 440      *
 441      * @return the current leader's id
 442      */
 443     protected String getLeaderId(){
 444         return currentBehavior.getLeaderId();
 445     }
 446
 447     protected RaftState getRaftState() {
 448         return currentBehavior.state();
 449     }
 450
 451     protected ReplicatedLogEntry getLastLogEntry() {
 452         return replicatedLog.last();
 453     }
 454
 455     protected Long getCurrentTerm(){
 456         return context.getTermInformation().getCurrentTerm();
 457     }
 458
 459     protected Long getCommitIndex(){
 460         return context.getCommitIndex();
 461     }
 462
 463     protected Long getLastApplied(){
 464         return context.getLastApplied();
 465     }
 466
 467     protected RaftActorContext getRaftActorContext() {
 468         return context;
 469     }
 470
 471     /**
 472      * setPeerAddress sets the address of a known peer at a later time.
 473      * <p>
 474      * This is to account for situations where a we know that a peer
 475      * exists but we do not know an address up-front. This may also be used in
 476      * situations where a known peer starts off in a different location and we
 477      * need to change it's address
 478      * <p>
 479      * Note that if the peerId does not match the list of peers passed to
 480      * this actor during construction an IllegalStateException will be thrown.
 481      *
 482      * @param peerId
 483      * @param peerAddress
 484      */
 485     protected void setPeerAddress(String peerId, String peerAddress){
 486         context.setPeerAddress(peerId, peerAddress);
 487     }
 488
 489
 490
 491     /**
 492      * The applyState method will be called by the RaftActor when some data
 493      * needs to be applied to the actor's state
 494      *
 495      * @param clientActor A reference to the client who sent this message. This
 496      *                    is the same reference that was passed to persistData
 497      *                    by the derived actor. clientActor may be null when
 498      *                    the RaftActor is behaving as a follower or during
 499      *                    recovery.
 500      * @param identifier  The identifier of the persisted data. This is also
 501      *                    the same identifier that was passed to persistData by
 502      *                    the derived actor. identifier may be null when
 503      *                    the RaftActor is behaving as a follower or during
 504      *                    recovery
 505      * @param data        A piece of data that was persisted by the persistData call.
 506      *                    This should NEVER be null.
 507      */
 508     protected abstract void applyState(ActorRef clientActor, String identifier,
 509         Object data);
 510
 511     /**
 512      * This method is called during recovery at the start of a batch of state entries. Derived
 513      * classes should perform any initialization needed to start a batch.
 514      */
 515     protected abstract void startLogRecoveryBatch(int maxBatchSize);
 516
 517     /**
 518      * This method is called during recovery to append state data to the current batch. This method
 519      * is called 1 or more times after {@link #startRecoveryStateBatch}.
 520      *
 521      * @param data the state data
 522      */
 523     protected abstract void appendRecoveredLogEntry(Payload data);
 524
 525     /**
 526      * This method is called during recovery to reconstruct the state of the actor.
 527      *
 528      * @param snapshot A snapshot of the state of the actor
 529      */
 530     protected abstract void applyRecoverySnapshot(ByteString snapshot);
 531
 532     /**
 533      * This method is called during recovery at the end of a batch to apply the current batched
 534      * log entries. This method is called after {@link #appendRecoveryLogEntry}.
 535      */
 536     protected abstract void applyCurrentLogRecoveryBatch();
 537
 538     /**
 539      * This method is called when recovery is complete.
 540      */
 541     protected abstract void onRecoveryComplete();
 542
 543     /**
 544      * This method will be called by the RaftActor when a snapshot needs to be
 545      * created. The derived actor should respond with its current state.
 546      * <p/>
 547      * During recovery the state that is returned by the derived actor will
 548      * be passed back to it by calling the applySnapshot  method
 549      *
 550      * @return The current state of the actor
 551      */
 552     protected abstract void createSnapshot();
 553
 554     /**
 555      * This method can be called at any other point during normal
 556      * operations when the derived actor is out of sync with it's peers
 557      * and the only way to bring it in sync is by applying a snapshot
 558      *
 559      * @param snapshot A snapshot of the state of the actor
 560      */
 561     protected abstract void applySnapshot(ByteString snapshot);
 562
 563     /**
 564      * This method will be called by the RaftActor when the state of the
 565      * RaftActor changes. The derived actor can then use methods like
 566      * isLeader or getLeader to do something useful
 567      */
 568     protected abstract void onStateChanged();
 569
 570     protected void onLeaderChanged(String oldLeader, String newLeader){};
 571
 572     private RaftActorBehavior switchBehavior(RaftState state) {
 573         if (currentBehavior != null) {
 574             if (currentBehavior.state() == state) {
 575                 return currentBehavior;
 576             }
 577             LOG.info("Switching from state " + currentBehavior.state() + " to "
 578                 + state);
 579
 580             try {
 581                 currentBehavior.close();
 582             } catch (Exception e) {
 583                 LOG.error(e,
 584                     "Failed to close behavior : " + currentBehavior.state());
 585             }
 586
 587         } else {
 588             LOG.info("Switching behavior to " + state);
 589         }
 590         RaftActorBehavior behavior = null;
 591         if (state == RaftState.Candidate) {
 592             behavior = new Candidate(context);
 593         } else if (state == RaftState.Follower) {
 594             behavior = new Follower(context);
 595         } else {
 596             behavior = new Leader(context);
 597         }
 598
 599
 600
 601         return behavior;
 602     }
 603
 604     private void trimPersistentData(long sequenceNumber) {
 605         // Trim akka snapshots
 606         // FIXME : Not sure how exactly the SnapshotSelectionCriteria is applied
 607         // For now guessing that it is ANDed.
 608         deleteSnapshots(new SnapshotSelectionCriteria(
 609             sequenceNumber - context.getConfigParams().getSnapshotBatchCount(), 43200000));
 610
 611         // Trim akka journal
 612         deleteMessages(sequenceNumber);
 613     }
 614
 615     private String getLeaderAddress(){
 616         if(isLeader()){
 617             return getSelf().path().toString();
 618         }
 619         String leaderId = currentBehavior.getLeaderId();
 620         if (leaderId == null) {
 621             return null;
 622         }
 623         String peerAddress = context.getPeerAddress(leaderId);
 624         if(LOG.isDebugEnabled()) {
 625             LOG.debug("getLeaderAddress leaderId = " + leaderId + " peerAddress = "
 626                 + peerAddress);
 627         }
 628
 629         return peerAddress;
 630     }
 631
 632     private void handleCaptureSnapshotReply(ByteString stateInBytes) {
 633         // create a snapshot object from the state provided and save it
 634         // when snapshot is saved async, SaveSnapshotSuccess is raised.
 635
 636         Snapshot sn = Snapshot.create(stateInBytes.toByteArray(),
 637             context.getReplicatedLog().getFrom(captureSnapshot.getLastAppliedIndex() + 1),
 638             captureSnapshot.getLastIndex(), captureSnapshot.getLastTerm(),
 639             captureSnapshot.getLastAppliedIndex(), captureSnapshot.getLastAppliedTerm());
 640
 641         saveSnapshot(sn);
 642
 643         LOG.info("Persisting of snapshot done:{}", sn.getLogMessage());
 644
 645         //be greedy and remove entries from in-mem journal which are in the snapshot
 646         // and update snapshotIndex and snapshotTerm without waiting for the success,
 647
 648         context.getReplicatedLog().snapshotPreCommit(stateInBytes,
 649             captureSnapshot.getLastAppliedIndex(),
 650             captureSnapshot.getLastAppliedTerm());
 651
 652         LOG.info("Removed in-memory snapshotted entries, adjusted snaphsotIndex:{} " +
 653             "and term:{}", captureSnapshot.getLastAppliedIndex(),
 654             captureSnapshot.getLastAppliedTerm());
 655
 656         captureSnapshot = null;
 657         hasSnapshotCaptureInitiated = false;
 658     }
 659
 660
 661     private class ReplicatedLogImpl extends AbstractReplicatedLogImpl {
 662
 663         public ReplicatedLogImpl(Snapshot snapshot) {
 664             super(ByteString.copyFrom(snapshot.getState()),
 665                 snapshot.getLastAppliedIndex(), snapshot.getLastAppliedTerm(),
 666                 snapshot.getUnAppliedEntries());
 667         }
 668
 669         public ReplicatedLogImpl() {
 670             super();
 671         }
 672
 673         @Override public void removeFromAndPersist(long logEntryIndex) {
 674             int adjustedIndex = adjustedIndex(logEntryIndex);
 675
 676             if (adjustedIndex < 0) {
 677                 return;
 678             }
 679
 680             // FIXME: Maybe this should be done after the command is saved
 681             journal.subList(adjustedIndex , journal.size()).clear();
 682
 683             persist(new DeleteEntries(adjustedIndex), new Procedure<DeleteEntries>(){
 684
 685                 @Override public void apply(DeleteEntries param)
 686                     throws Exception {
 687                     //FIXME : Doing nothing for now
 688                 }
 689             });
 690         }
 691
 692         @Override public void appendAndPersist(
 693             final ReplicatedLogEntry replicatedLogEntry) {
 694             appendAndPersist(null, null, replicatedLogEntry);
 695         }
 696
 697         public void appendAndPersist(final ActorRef clientActor,
 698             final String identifier,
 699             final ReplicatedLogEntry replicatedLogEntry) {
 700             context.getLogger().debug(
 701                 "Append log entry and persist {} ", replicatedLogEntry);
 702             // FIXME : By adding the replicated log entry to the in-memory journal we are not truly ensuring durability of the logs
 703             journal.add(replicatedLogEntry);
 704
 705             // When persisting events with persist it is guaranteed that the
 706             // persistent actor will not receive further commands between the
 707             // persist call and the execution(s) of the associated event
 708             // handler. This also holds for multiple persist calls in context
 709             // of a single command.
 710             persist(replicatedLogEntry,
 711                 new Procedure<ReplicatedLogEntry>() {
 712                     @Override
 713                     public void apply(ReplicatedLogEntry evt) throws Exception {
 714                         // when a snaphsot is being taken, captureSnapshot != null
 715                         if (hasSnapshotCaptureInitiated == false &&
 716                             journal.size() % context.getConfigParams().getSnapshotBatchCount() == 0) {
 717
 718                             LOG.info("Initiating Snapshot Capture..");
 719                             long lastAppliedIndex = -1;
 720                             long lastAppliedTerm = -1;
 721
 722                             ReplicatedLogEntry lastAppliedEntry = get(context.getLastApplied());
 723                             if (lastAppliedEntry != null) {
 724                                 lastAppliedIndex = lastAppliedEntry.getIndex();
 725                                 lastAppliedTerm = lastAppliedEntry.getTerm();
 726                             }
 727
 728                             if(LOG.isDebugEnabled()) {
 729                                 LOG.debug("Snapshot Capture logSize: {}", journal.size());
 730                                 LOG.debug("Snapshot Capture lastApplied:{} ",
 731                                     context.getLastApplied());
 732                                 LOG.debug("Snapshot Capture lastAppliedIndex:{}", lastAppliedIndex);
 733                                 LOG.debug("Snapshot Capture lastAppliedTerm:{}", lastAppliedTerm);
 734                             }
 735
 736                             // send a CaptureSnapshot to self to make the expensive operation async.
 737                             getSelf().tell(new CaptureSnapshot(
 738                                 lastIndex(), lastTerm(), lastAppliedIndex, lastAppliedTerm),
 739                                 null);
 740                             hasSnapshotCaptureInitiated = true;
 741                         }
 742                         // Send message for replication
 743                         if (clientActor != null) {
 744                             currentBehavior.handleMessage(getSelf(),
 745                                 new Replicate(clientActor, identifier,
 746                                     replicatedLogEntry)
 747                             );
 748                         }
 749                     }
 750                 }
 751             );
 752         }
 753
 754     }
 755
 756     private static class DeleteEntries implements Serializable {
 757         private final int fromIndex;
 758
 759
 760         public DeleteEntries(int fromIndex) {
 761             this.fromIndex = fromIndex;
 762         }
 763
 764         public int getFromIndex() {
 765             return fromIndex;
 766         }
 767     }
 768
 769
 770     private class ElectionTermImpl implements ElectionTerm {
 771         /**
 772          * Identifier of the actor whose election term information this is
 773          */
 774         private long currentTerm = 0;
 775         private String votedFor = null;
 776
 777         @Override
 778         public long getCurrentTerm() {
 779             return currentTerm;
 780         }
 781
 782         @Override
 783         public String getVotedFor() {
 784             return votedFor;
 785         }
 786
 787         @Override public void update(long currentTerm, String votedFor) {
 788             if(LOG.isDebugEnabled()) {
 789                 LOG.debug("Set currentTerm={}, votedFor={}", currentTerm, votedFor);
 790             }
 791             this.currentTerm = currentTerm;
 792             this.votedFor = votedFor;
 793         }
 794
 795         @Override
 796         public void updateAndPersist(long currentTerm, String votedFor){
 797             update(currentTerm, votedFor);
 798             // FIXME : Maybe first persist then update the state
 799             persist(new UpdateElectionTerm(this.currentTerm, this.votedFor), new Procedure<UpdateElectionTerm>(){
 800
 801                 @Override public void apply(UpdateElectionTerm param)
 802                     throws Exception {
 803
 804                 }
 805             });
 806         }
 807     }
 808
 809     private static class UpdateElectionTerm implements Serializable {
 810         private final long currentTerm;
 811         private final String votedFor;
 812
 813         public UpdateElectionTerm(long currentTerm, String votedFor) {
 814             this.currentTerm = currentTerm;
 815             this.votedFor = votedFor;
 816         }
 817
 818         public long getCurrentTerm() {
 819             return currentTerm;
 820         }
 821
 822         public String getVotedFor() {
 823             return votedFor;
 824         }
 825     }
 826
 827 }