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