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.ApplyLogEntries;
  25 import org.opendaylight.controller.cluster.raft.base.messages.ApplySnapshot;
  26 import org.opendaylight.controller.cluster.raft.base.messages.ApplyState;
  27 import org.opendaylight.controller.cluster.raft.base.messages.CaptureSnapshot;
  28 import org.opendaylight.controller.cluster.raft.base.messages.CaptureSnapshotReply;
  29 import org.opendaylight.controller.cluster.raft.base.messages.Replicate;
  30 import org.opendaylight.controller.cluster.raft.base.messages.SendHeartBeat;
  31 import org.opendaylight.controller.cluster.raft.behaviors.Candidate;
  32 import org.opendaylight.controller.cluster.raft.behaviors.Follower;
  33 import org.opendaylight.controller.cluster.raft.behaviors.Leader;
  34 import org.opendaylight.controller.cluster.raft.behaviors.RaftActorBehavior;
  35 import org.opendaylight.controller.cluster.raft.client.messages.AddRaftPeer;
  36 import org.opendaylight.controller.cluster.raft.client.messages.FindLeader;
  37 import org.opendaylight.controller.cluster.raft.client.messages.FindLeaderReply;
  38 import org.opendaylight.controller.cluster.raft.client.messages.RemoveRaftPeer;
  39 import org.opendaylight.controller.cluster.raft.messages.AppendEntriesReply;
  40 import org.opendaylight.controller.cluster.raft.protobuff.client.messages.Payload;
  41 import org.opendaylight.controller.protobuff.messages.cluster.raft.AppendEntriesMessages;
  42
  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     protected 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     public RaftActor(String id, Map<String, String> peerAddresses) {
 112         this(id, peerAddresses, Optional.<ConfigParams>absent());
 113     }
 114
 115     public RaftActor(String id, Map<String, String> peerAddresses,
 116          Optional<ConfigParams> configParams) {
 117
 118         context = new RaftActorContextImpl(this.getSelf(),
 119             this.getContext(), id, new ElectionTermImpl(),
 120             -1, -1, replicatedLog, peerAddresses,
 121             (configParams.isPresent() ? configParams.get(): new DefaultConfigParamsImpl()),
 122             LOG);
 123     }
 124
 125     @Override public void onReceiveRecover(Object message) {
 126         if (message instanceof SnapshotOffer) {
 127             LOG.info("SnapshotOffer called..");
 128             SnapshotOffer offer = (SnapshotOffer) message;
 129             Snapshot snapshot = (Snapshot) offer.snapshot();
 130
 131             // Create a replicated log with the snapshot information
 132             // The replicated log can be used later on to retrieve this snapshot
 133             // when we need to install it on a peer
 134             replicatedLog = new ReplicatedLogImpl(snapshot);
 135
 136             context.setReplicatedLog(replicatedLog);
 137             context.setLastApplied(snapshot.getLastAppliedIndex());
 138             context.setCommitIndex(snapshot.getLastAppliedIndex());
 139
 140             LOG.info("Applied snapshot to replicatedLog. " +
 141                     "snapshotIndex={}, snapshotTerm={}, journal-size={}",
 142                 replicatedLog.snapshotIndex, replicatedLog.snapshotTerm,
 143                 replicatedLog.size()
 144             );
 145
 146             // Apply the snapshot to the actors state
 147             applySnapshot(ByteString.copyFrom(snapshot.getState()));
 148
 149         } else if (message instanceof ReplicatedLogEntry) {
 150             ReplicatedLogEntry logEntry = (ReplicatedLogEntry) message;
 151             if(LOG.isDebugEnabled()) {
 152                 LOG.debug("Received ReplicatedLogEntry for recovery:{}", logEntry.getIndex());
 153             }
 154             replicatedLog.append(logEntry);
 155
 156         } else if (message instanceof ApplyLogEntries) {
 157             ApplyLogEntries ale = (ApplyLogEntries) message;
 158
 159             if(LOG.isDebugEnabled()) {
 160                 LOG.debug("Received ApplyLogEntries for recovery, applying to state:{} to {}",
 161                     context.getLastApplied() + 1, ale.getToIndex());
 162             }
 163
 164             for (long i = context.getLastApplied() + 1; i <= ale.getToIndex(); i++) {
 165                 applyState(null, "recovery", replicatedLog.get(i).getData());
 166             }
 167             context.setLastApplied(ale.getToIndex());
 168             context.setCommitIndex(ale.getToIndex());
 169
 170         } else if (message instanceof DeleteEntries) {
 171             replicatedLog.removeFrom(((DeleteEntries) message).getFromIndex());
 172
 173         } else if (message instanceof UpdateElectionTerm) {
 174             context.getTermInformation().update(((UpdateElectionTerm) message).getCurrentTerm(),
 175                 ((UpdateElectionTerm) message).getVotedFor());
 176
 177         } else if (message instanceof RecoveryCompleted) {
 178             LOG.info(
 179                 "RecoveryCompleted - Switching actor to Follower - " +
 180                     "Persistence Id =  " + persistenceId() +
 181                     " Last index in log:{}, snapshotIndex={}, snapshotTerm={}, " +
 182                     "journal-size={}",
 183                 replicatedLog.lastIndex(), replicatedLog.snapshotIndex,
 184                 replicatedLog.snapshotTerm, replicatedLog.size());
 185             currentBehavior = switchBehavior(RaftState.Follower);
 186             onStateChanged();
 187         }
 188     }
 189
 190     @Override public void onReceiveCommand(Object message) {
 191         if (message instanceof ApplyState){
 192             ApplyState applyState = (ApplyState) message;
 193
 194             if(LOG.isDebugEnabled()) {
 195                 LOG.debug("Applying state for log index {} data {}",
 196                     applyState.getReplicatedLogEntry().getIndex(),
 197                     applyState.getReplicatedLogEntry().getData());
 198             }
 199
 200             applyState(applyState.getClientActor(), applyState.getIdentifier(),
 201                 applyState.getReplicatedLogEntry().getData());
 202
 203         } else if (message instanceof ApplyLogEntries){
 204             ApplyLogEntries ale = (ApplyLogEntries) message;
 205             if(LOG.isDebugEnabled()) {
 206                 LOG.debug("Persisting ApplyLogEntries with index={}", ale.getToIndex());
 207             }
 208             persist(new ApplyLogEntries(ale.getToIndex()), new Procedure<ApplyLogEntries>() {
 209                 @Override
 210                 public void apply(ApplyLogEntries param) throws Exception {
 211                 }
 212             });
 213
 214         } else if(message instanceof ApplySnapshot ) {
 215             Snapshot snapshot = ((ApplySnapshot) message).getSnapshot();
 216
 217             if(LOG.isDebugEnabled()) {
 218                 LOG.debug("ApplySnapshot called on Follower Actor " +
 219                         "snapshotIndex:{}, snapshotTerm:{}", snapshot.getLastAppliedIndex(),
 220                     snapshot.getLastAppliedTerm()
 221                 );
 222             }
 223             applySnapshot(ByteString.copyFrom(snapshot.getState()));
 224
 225             //clears the followers log, sets the snapshot index to ensure adjusted-index works
 226             replicatedLog = new ReplicatedLogImpl(snapshot);
 227             context.setReplicatedLog(replicatedLog);
 228             context.setLastApplied(snapshot.getLastAppliedIndex());
 229
 230         } else if (message instanceof FindLeader) {
 231             getSender().tell(
 232                 new FindLeaderReply(getLeaderAddress()),
 233                 getSelf()
 234             );
 235
 236         } else if (message instanceof SaveSnapshotSuccess) {
 237             SaveSnapshotSuccess success = (SaveSnapshotSuccess) message;
 238             LOG.info("SaveSnapshotSuccess received for snapshot");
 239
 240             context.getReplicatedLog().snapshotCommit();
 241
 242             // TODO: Not sure if we want to be this aggressive with trimming stuff
 243             trimPersistentData(success.metadata().sequenceNr());
 244
 245         } else if (message instanceof SaveSnapshotFailure) {
 246             SaveSnapshotFailure saveSnapshotFailure = (SaveSnapshotFailure) message;
 247
 248             LOG.info("saveSnapshotFailure.metadata():{}", saveSnapshotFailure.metadata().toString());
 249             LOG.error(saveSnapshotFailure.cause(), "SaveSnapshotFailure received for snapshot Cause:");
 250
 251             context.getReplicatedLog().snapshotRollback();
 252
 253             LOG.info("Replicated Log rollbacked. Snapshot will be attempted in the next cycle." +
 254                 "snapshotIndex:{}, snapshotTerm:{}, log-size:{}",
 255                 context.getReplicatedLog().getSnapshotIndex(),
 256                 context.getReplicatedLog().getSnapshotTerm(),
 257                 context.getReplicatedLog().size());
 258
 259         } else if (message instanceof AddRaftPeer){
 260
 261             // FIXME : Do not add raft peers like this.
 262             // When adding a new Peer we have to ensure that the a majority of
 263             // the peers know about the new Peer. Doing it this way may cause
 264             // a situation where multiple Leaders may emerge
 265             AddRaftPeer arp = (AddRaftPeer)message;
 266            context.addToPeers(arp.getName(), arp.getAddress());
 267
 268         } else if (message instanceof RemoveRaftPeer){
 269
 270             RemoveRaftPeer rrp = (RemoveRaftPeer)message;
 271             context.removePeer(rrp.getName());
 272
 273         } else if (message instanceof CaptureSnapshot) {
 274             LOG.info("CaptureSnapshot received by actor");
 275             CaptureSnapshot cs = (CaptureSnapshot)message;
 276             captureSnapshot = cs;
 277             createSnapshot();
 278
 279         } else if (message instanceof CaptureSnapshotReply){
 280             LOG.info("CaptureSnapshotReply received by actor");
 281             CaptureSnapshotReply csr = (CaptureSnapshotReply) message;
 282
 283             ByteString stateInBytes = csr.getSnapshot();
 284             LOG.info("CaptureSnapshotReply stateInBytes size:{}", stateInBytes.size());
 285             handleCaptureSnapshotReply(stateInBytes);
 286
 287         } else {
 288             if (!(message instanceof AppendEntriesMessages.AppendEntries)
 289                 && !(message instanceof AppendEntriesReply) && !(message instanceof SendHeartBeat)) {
 290                 if(LOG.isDebugEnabled()) {
 291                     LOG.debug("onReceiveCommand: message:" + message.getClass());
 292                 }
 293             }
 294
 295             RaftState state =
 296                 currentBehavior.handleMessage(getSender(), message);
 297             RaftActorBehavior oldBehavior = currentBehavior;
 298             currentBehavior = switchBehavior(state);
 299             if(oldBehavior != currentBehavior){
 300                 onStateChanged();
 301             }
 302
 303             onLeaderChanged(oldBehavior.getLeaderId(), currentBehavior.getLeaderId());
 304         }
 305     }
 306
 307     public java.util.Set<String> getPeers() {
 308         return context.getPeerAddresses().keySet();
 309     }
 310
 311     protected String getReplicatedLogState() {
 312         return "snapshotIndex=" + context.getReplicatedLog().getSnapshotIndex()
 313             + ", snapshotTerm=" + context.getReplicatedLog().getSnapshotTerm()
 314             + ", im-mem journal size=" + context.getReplicatedLog().size();
 315     }
 316
 317
 318     /**
 319      * When a derived RaftActor needs to persist something it must call
 320      * persistData.
 321      *
 322      * @param clientActor
 323      * @param identifier
 324      * @param data
 325      */
 326     protected void persistData(ActorRef clientActor, String identifier,
 327         Payload data) {
 328
 329         ReplicatedLogEntry replicatedLogEntry = new ReplicatedLogImplEntry(
 330             context.getReplicatedLog().lastIndex() + 1,
 331             context.getTermInformation().getCurrentTerm(), data);
 332
 333         if(LOG.isDebugEnabled()) {
 334             LOG.debug("Persist data {}", replicatedLogEntry);
 335         }
 336
 337         replicatedLog
 338             .appendAndPersist(clientActor, identifier, replicatedLogEntry);
 339     }
 340
 341     protected String getId() {
 342         return context.getId();
 343     }
 344
 345     /**
 346      * Derived actors can call the isLeader method to check if the current
 347      * RaftActor is the Leader or not
 348      *
 349      * @return true it this RaftActor is a Leader false otherwise
 350      */
 351     protected boolean isLeader() {
 352         return context.getId().equals(currentBehavior.getLeaderId());
 353     }
 354
 355     /**
 356      * Derived actor can call getLeader if they need a reference to the Leader.
 357      * This would be useful for example in forwarding a request to an actor
 358      * which is the leader
 359      *
 360      * @return A reference to the leader if known, null otherwise
 361      */
 362     protected ActorSelection getLeader(){
 363         String leaderAddress = getLeaderAddress();
 364
 365         if(leaderAddress == null){
 366             return null;
 367         }
 368
 369         return context.actorSelection(leaderAddress);
 370     }
 371
 372     /**
 373      *
 374      * @return the current leader's id
 375      */
 376     protected String getLeaderId(){
 377         return currentBehavior.getLeaderId();
 378     }
 379
 380     protected RaftState getRaftState() {
 381         return currentBehavior.state();
 382     }
 383
 384     protected ReplicatedLogEntry getLastLogEntry() {
 385         return replicatedLog.last();
 386     }
 387
 388     protected Long getCurrentTerm(){
 389         return context.getTermInformation().getCurrentTerm();
 390     }
 391
 392     protected Long getCommitIndex(){
 393         return context.getCommitIndex();
 394     }
 395
 396     protected Long getLastApplied(){
 397         return context.getLastApplied();
 398     }
 399
 400     /**
 401      * setPeerAddress sets the address of a known peer at a later time.
 402      * <p>
 403      * This is to account for situations where a we know that a peer
 404      * exists but we do not know an address up-front. This may also be used in
 405      * situations where a known peer starts off in a different location and we
 406      * need to change it's address
 407      * <p>
 408      * Note that if the peerId does not match the list of peers passed to
 409      * this actor during construction an IllegalStateException will be thrown.
 410      *
 411      * @param peerId
 412      * @param peerAddress
 413      */
 414     protected void setPeerAddress(String peerId, String peerAddress){
 415         context.setPeerAddress(peerId, peerAddress);
 416     }
 417
 418
 419
 420     /**
 421      * The applyState method will be called by the RaftActor when some data
 422      * needs to be applied to the actor's state
 423      *
 424      * @param clientActor A reference to the client who sent this message. This
 425      *                    is the same reference that was passed to persistData
 426      *                    by the derived actor. clientActor may be null when
 427      *                    the RaftActor is behaving as a follower or during
 428      *                    recovery.
 429      * @param identifier  The identifier of the persisted data. This is also
 430      *                    the same identifier that was passed to persistData by
 431      *                    the derived actor. identifier may be null when
 432      *                    the RaftActor is behaving as a follower or during
 433      *                    recovery
 434      * @param data        A piece of data that was persisted by the persistData call.
 435      *                    This should NEVER be null.
 436      */
 437     protected abstract void applyState(ActorRef clientActor, String identifier,
 438         Object data);
 439
 440     /**
 441      * This method will be called by the RaftActor when a snapshot needs to be
 442      * created. The derived actor should respond with its current state.
 443      * <p/>
 444      * During recovery the state that is returned by the derived actor will
 445      * be passed back to it by calling the applySnapshot  method
 446      *
 447      * @return The current state of the actor
 448      */
 449     protected abstract void createSnapshot();
 450
 451     /**
 452      * This method will be called by the RaftActor during recovery to
 453      * reconstruct the state of the actor.
 454      * <p/>
 455      * This method may also be called at any other point during normal
 456      * operations when the derived actor is out of sync with it's peers
 457      * and the only way to bring it in sync is by applying a snapshot
 458      *
 459      * @param snapshot A snapshot of the state of the actor
 460      */
 461     protected abstract void applySnapshot(ByteString snapshot);
 462
 463     /**
 464      * This method will be called by the RaftActor when the state of the
 465      * RaftActor changes. The derived actor can then use methods like
 466      * isLeader or getLeader to do something useful
 467      */
 468     protected abstract void onStateChanged();
 469
 470     protected void onLeaderChanged(String oldLeader, String newLeader){};
 471
 472     private RaftActorBehavior switchBehavior(RaftState state) {
 473         if (currentBehavior != null) {
 474             if (currentBehavior.state() == state) {
 475                 return currentBehavior;
 476             }
 477             LOG.info("Switching from state " + currentBehavior.state() + " to "
 478                 + state);
 479
 480             try {
 481                 currentBehavior.close();
 482             } catch (Exception e) {
 483                 LOG.error(e,
 484                     "Failed to close behavior : " + currentBehavior.state());
 485             }
 486
 487         } else {
 488             LOG.info("Switching behavior to " + state);
 489         }
 490         RaftActorBehavior behavior = null;
 491         if (state == RaftState.Candidate) {
 492             behavior = new Candidate(context);
 493         } else if (state == RaftState.Follower) {
 494             behavior = new Follower(context);
 495         } else {
 496             behavior = new Leader(context);
 497         }
 498
 499
 500
 501         return behavior;
 502     }
 503
 504     private void trimPersistentData(long sequenceNumber) {
 505         // Trim akka snapshots
 506         // FIXME : Not sure how exactly the SnapshotSelectionCriteria is applied
 507         // For now guessing that it is ANDed.
 508         deleteSnapshots(new SnapshotSelectionCriteria(
 509             sequenceNumber - context.getConfigParams().getSnapshotBatchCount(), 43200000));
 510
 511         // Trim akka journal
 512         deleteMessages(sequenceNumber);
 513     }
 514
 515     private String getLeaderAddress(){
 516         if(isLeader()){
 517             return getSelf().path().toString();
 518         }
 519         String leaderId = currentBehavior.getLeaderId();
 520         if (leaderId == null) {
 521             return null;
 522         }
 523         String peerAddress = context.getPeerAddress(leaderId);
 524         if(LOG.isDebugEnabled()) {
 525             LOG.debug("getLeaderAddress leaderId = " + leaderId + " peerAddress = "
 526                 + peerAddress);
 527         }
 528
 529         return peerAddress;
 530     }
 531
 532     private void handleCaptureSnapshotReply(ByteString stateInBytes) {
 533         // create a snapshot object from the state provided and save it
 534         // when snapshot is saved async, SaveSnapshotSuccess is raised.
 535
 536         Snapshot sn = Snapshot.create(stateInBytes.toByteArray(),
 537             context.getReplicatedLog().getFrom(captureSnapshot.getLastAppliedIndex() + 1),
 538             captureSnapshot.getLastIndex(), captureSnapshot.getLastTerm(),
 539             captureSnapshot.getLastAppliedIndex(), captureSnapshot.getLastAppliedTerm());
 540
 541         saveSnapshot(sn);
 542
 543         LOG.info("Persisting of snapshot done:{}", sn.getLogMessage());
 544
 545         //be greedy and remove entries from in-mem journal which are in the snapshot
 546         // and update snapshotIndex and snapshotTerm without waiting for the success,
 547
 548         context.getReplicatedLog().snapshotPreCommit(stateInBytes,
 549             captureSnapshot.getLastAppliedIndex(),
 550             captureSnapshot.getLastAppliedTerm());
 551
 552         LOG.info("Removed in-memory snapshotted entries, adjusted snaphsotIndex:{} " +
 553             "and term:{}", captureSnapshot.getLastAppliedIndex(),
 554             captureSnapshot.getLastAppliedTerm());
 555
 556         captureSnapshot = null;
 557         hasSnapshotCaptureInitiated = false;
 558     }
 559
 560
 561     private class ReplicatedLogImpl extends AbstractReplicatedLogImpl {
 562
 563         public ReplicatedLogImpl(Snapshot snapshot) {
 564             super(ByteString.copyFrom(snapshot.getState()),
 565                 snapshot.getLastAppliedIndex(), snapshot.getLastAppliedTerm(),
 566                 snapshot.getUnAppliedEntries());
 567         }
 568
 569         public ReplicatedLogImpl() {
 570             super();
 571         }
 572
 573         @Override public void removeFromAndPersist(long logEntryIndex) {
 574             int adjustedIndex = adjustedIndex(logEntryIndex);
 575
 576             if (adjustedIndex < 0) {
 577                 return;
 578             }
 579
 580             // FIXME: Maybe this should be done after the command is saved
 581             journal.subList(adjustedIndex , journal.size()).clear();
 582
 583             persist(new DeleteEntries(adjustedIndex), new Procedure<DeleteEntries>(){
 584
 585                 @Override public void apply(DeleteEntries param)
 586                     throws Exception {
 587                     //FIXME : Doing nothing for now
 588                 }
 589             });
 590         }
 591
 592         @Override public void appendAndPersist(
 593             final ReplicatedLogEntry replicatedLogEntry) {
 594             appendAndPersist(null, null, replicatedLogEntry);
 595         }
 596
 597         public void appendAndPersist(final ActorRef clientActor,
 598             final String identifier,
 599             final ReplicatedLogEntry replicatedLogEntry) {
 600             context.getLogger().debug(
 601                 "Append log entry and persist {} ", replicatedLogEntry);
 602             // FIXME : By adding the replicated log entry to the in-memory journal we are not truly ensuring durability of the logs
 603             journal.add(replicatedLogEntry);
 604
 605             // When persisting events with persist it is guaranteed that the
 606             // persistent actor will not receive further commands between the
 607             // persist call and the execution(s) of the associated event
 608             // handler. This also holds for multiple persist calls in context
 609             // of a single command.
 610             persist(replicatedLogEntry,
 611                 new Procedure<ReplicatedLogEntry>() {
 612                     public void apply(ReplicatedLogEntry evt) throws Exception {
 613                         // when a snaphsot is being taken, captureSnapshot != null
 614                         if (hasSnapshotCaptureInitiated == false &&
 615                             journal.size() % context.getConfigParams().getSnapshotBatchCount() == 0) {
 616
 617                             LOG.info("Initiating Snapshot Capture..");
 618                             long lastAppliedIndex = -1;
 619                             long lastAppliedTerm = -1;
 620
 621                             ReplicatedLogEntry lastAppliedEntry = get(context.getLastApplied());
 622                             if (lastAppliedEntry != null) {
 623                                 lastAppliedIndex = lastAppliedEntry.getIndex();
 624                                 lastAppliedTerm = lastAppliedEntry.getTerm();
 625                             }
 626
 627                             if(LOG.isDebugEnabled()) {
 628                                 LOG.debug("Snapshot Capture logSize: {}", journal.size());
 629                                 LOG.debug("Snapshot Capture lastApplied:{} ",
 630                                     context.getLastApplied());
 631                                 LOG.debug("Snapshot Capture lastAppliedIndex:{}", lastAppliedIndex);
 632                                 LOG.debug("Snapshot Capture lastAppliedTerm:{}", lastAppliedTerm);
 633                             }
 634
 635                             // send a CaptureSnapshot to self to make the expensive operation async.
 636                             getSelf().tell(new CaptureSnapshot(
 637                                 lastIndex(), lastTerm(), lastAppliedIndex, lastAppliedTerm),
 638                                 null);
 639                             hasSnapshotCaptureInitiated = true;
 640                         }
 641                         // Send message for replication
 642                         if (clientActor != null) {
 643                             currentBehavior.handleMessage(getSelf(),
 644                                 new Replicate(clientActor, identifier,
 645                                     replicatedLogEntry)
 646                             );
 647                         }
 648                     }
 649                 }
 650             );
 651         }
 652
 653     }
 654
 655     private static class DeleteEntries implements Serializable {
 656         private final int fromIndex;
 657
 658
 659         public DeleteEntries(int fromIndex) {
 660             this.fromIndex = fromIndex;
 661         }
 662
 663         public int getFromIndex() {
 664             return fromIndex;
 665         }
 666     }
 667
 668
 669     private class ElectionTermImpl implements ElectionTerm {
 670         /**
 671          * Identifier of the actor whose election term information this is
 672          */
 673         private long currentTerm = 0;
 674         private String votedFor = null;
 675
 676         public long getCurrentTerm() {
 677             return currentTerm;
 678         }
 679
 680         public String getVotedFor() {
 681             return votedFor;
 682         }
 683
 684         @Override public void update(long currentTerm, String votedFor) {
 685             if(LOG.isDebugEnabled()) {
 686                 LOG.debug("Set currentTerm={}, votedFor={}", currentTerm, votedFor);
 687             }
 688             this.currentTerm = currentTerm;
 689             this.votedFor = votedFor;
 690         }
 691
 692         @Override
 693         public void updateAndPersist(long currentTerm, String votedFor){
 694             update(currentTerm, votedFor);
 695             // FIXME : Maybe first persist then update the state
 696             persist(new UpdateElectionTerm(this.currentTerm, this.votedFor), new Procedure<UpdateElectionTerm>(){
 697
 698                 @Override public void apply(UpdateElectionTerm param)
 699                     throws Exception {
 700
 701                 }
 702             });
 703         }
 704     }
 705
 706     private static class UpdateElectionTerm implements Serializable {
 707         private final long currentTerm;
 708         private final String votedFor;
 709
 710         public UpdateElectionTerm(long currentTerm, String votedFor) {
 711             this.currentTerm = currentTerm;
 712             this.votedFor = votedFor;
 713         }
 714
 715         public long getCurrentTerm() {
 716             return currentTerm;
 717         }
 718
 719         public String getVotedFor() {
 720             return votedFor;
 721         }
 722     }
 723
 724 }