opendaylight/md-sal/sal-akka-raft/src/main/java/org/opendaylight/controller/cluster/raft/behaviors/AbstractLeader.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.behaviors;
  10
  11 import akka.actor.ActorRef;
  12 import akka.actor.ActorSelection;
  13 import akka.actor.Cancellable;
  14 import com.google.common.annotations.VisibleForTesting;
  15 import com.google.common.base.Optional;
  16 import com.google.common.base.Preconditions;
  17 import com.google.protobuf.ByteString;
  18 import java.io.IOException;
  19 import java.util.ArrayList;
  20 import java.util.Collections;
  21 import java.util.HashMap;
  22 import java.util.List;
  23 import java.util.Map;
  24 import java.util.Set;
  25 import java.util.concurrent.TimeUnit;
  26 import java.util.concurrent.atomic.AtomicLong;
  27 import org.opendaylight.controller.cluster.raft.ClientRequestTracker;
  28 import org.opendaylight.controller.cluster.raft.ClientRequestTrackerImpl;
  29 import org.opendaylight.controller.cluster.raft.FollowerLogInformation;
  30 import org.opendaylight.controller.cluster.raft.FollowerLogInformationImpl;
  31 import org.opendaylight.controller.cluster.raft.RaftActorContext;
  32 import org.opendaylight.controller.cluster.raft.RaftState;
  33 import org.opendaylight.controller.cluster.raft.ReplicatedLogEntry;
  34 import org.opendaylight.controller.cluster.raft.base.messages.CaptureSnapshot;
  35 import org.opendaylight.controller.cluster.raft.base.messages.InitiateInstallSnapshot;
  36 import org.opendaylight.controller.cluster.raft.base.messages.Replicate;
  37 import org.opendaylight.controller.cluster.raft.base.messages.SendHeartBeat;
  38 import org.opendaylight.controller.cluster.raft.base.messages.SendInstallSnapshot;
  39 import org.opendaylight.controller.cluster.raft.messages.AppendEntries;
  40 import org.opendaylight.controller.cluster.raft.messages.AppendEntriesReply;
  41 import org.opendaylight.controller.cluster.raft.messages.InstallSnapshot;
  42 import org.opendaylight.controller.cluster.raft.messages.InstallSnapshotReply;
  43 import org.opendaylight.controller.cluster.raft.messages.RaftRPC;
  44 import org.opendaylight.controller.cluster.raft.messages.RequestVoteReply;
  45 import scala.concurrent.duration.FiniteDuration;
  46
  47 /**
  48  * The behavior of a RaftActor when it is in the Leader state
  49  * <p/>
  50  * Leaders:
  51  * <ul>
  52  * <li> Upon election: send initial empty AppendEntries RPCs
  53  * (heartbeat) to each server; repeat during idle periods to
  54  * prevent election timeouts (§5.2)
  55  * <li> If command received from client: append entry to local log,
  56  * respond after entry applied to state machine (§5.3)
  57  * <li> If last log index ≥ nextIndex for a follower: send
  58  * AppendEntries RPC with log entries starting at nextIndex
  59  * <ul>
  60  * <li> If successful: update nextIndex and matchIndex for
  61  * follower (§5.3)
  62  * <li> If AppendEntries fails because of log inconsistency:
  63  * decrement nextIndex and retry (§5.3)
  64  * </ul>
  65  * <li> If there exists an N such that N > commitIndex, a majority
  66  * of matchIndex[i] ≥ N, and log[N].term == currentTerm:
  67  * set commitIndex = N (§5.3, §5.4).
  68  */
  69 public abstract class AbstractLeader extends AbstractRaftActorBehavior {
  70     protected final Map<String, FollowerLogInformation> followerToLog = new HashMap<>();
  71     protected final Map<String, FollowerToSnapshot> mapFollowerToSnapshot = new HashMap<>();
  72
  73     protected final Set<String> followers;
  74
  75     private Cancellable heartbeatSchedule = null;
  76
  77     private List<ClientRequestTracker> trackerList = new ArrayList<>();
  78
  79     protected final int minReplicationCount;
  80
  81     protected final int minIsolatedLeaderPeerCount;
  82
  83     private Optional<ByteString> snapshot;
  84
  85     public AbstractLeader(RaftActorContext context) {
  86         super(context);
  87
  88         followers = context.getPeerAddresses().keySet();
  89
  90         for (String followerId : followers) {
  91             FollowerLogInformation followerLogInformation =
  92                 new FollowerLogInformationImpl(followerId,
  93                     new AtomicLong(context.getCommitIndex()),
  94                     new AtomicLong(-1),
  95                     context.getConfigParams().getElectionTimeOutInterval());
  96
  97             followerToLog.put(followerId, followerLogInformation);
  98         }
  99
 100         leaderId = context.getId();
 101
 102         if(LOG.isDebugEnabled()) {
 103             LOG.debug("Election:Leader has following peers: {}", followers);
 104         }
 105
 106         minReplicationCount = getMajorityVoteCount(followers.size());
 107
 108         // the isolated Leader peer count will be 1 less than the majority vote count.
 109         // this is because the vote count has the self vote counted in it
 110         // for e.g
 111         // 0 peers = 1 votesRequired , minIsolatedLeaderPeerCount = 0
 112         // 2 peers = 2 votesRequired , minIsolatedLeaderPeerCount = 1
 113         // 4 peers = 3 votesRequired, minIsolatedLeaderPeerCount = 2
 114         minIsolatedLeaderPeerCount = minReplicationCount > 0 ? (minReplicationCount - 1) : 0;
 115
 116         snapshot = Optional.absent();
 117
 118         // Immediately schedule a heartbeat
 119         // Upon election: send initial empty AppendEntries RPCs
 120         // (heartbeat) to each server; repeat during idle periods to
 121         // prevent election timeouts (§5.2)
 122         scheduleHeartBeat(new FiniteDuration(0, TimeUnit.SECONDS));
 123     }
 124
 125     private Optional<ByteString> getSnapshot() {
 126         return snapshot;
 127     }
 128
 129     @VisibleForTesting
 130     void setSnapshot(Optional<ByteString> snapshot) {
 131         this.snapshot = snapshot;
 132     }
 133
 134     @Override
 135     protected RaftActorBehavior handleAppendEntries(ActorRef sender,
 136         AppendEntries appendEntries) {
 137
 138         if(LOG.isDebugEnabled()) {
 139             LOG.debug(appendEntries.toString());
 140         }
 141
 142         return this;
 143     }
 144
 145     @Override
 146     protected RaftActorBehavior handleAppendEntriesReply(ActorRef sender,
 147         AppendEntriesReply appendEntriesReply) {
 148
 149         if(! appendEntriesReply.isSuccess()) {
 150             if(LOG.isDebugEnabled()) {
 151                 LOG.debug(appendEntriesReply.toString());
 152             }
 153         }
 154
 155         // Update the FollowerLogInformation
 156         String followerId = appendEntriesReply.getFollowerId();
 157         FollowerLogInformation followerLogInformation =
 158             followerToLog.get(followerId);
 159
 160         if(followerLogInformation == null){
 161             LOG.error("Unknown follower {}", followerId);
 162             return this;
 163         }
 164
 165         followerLogInformation.markFollowerActive();
 166
 167         if (appendEntriesReply.isSuccess()) {
 168             followerLogInformation
 169                 .setMatchIndex(appendEntriesReply.getLogLastIndex());
 170             followerLogInformation
 171                 .setNextIndex(appendEntriesReply.getLogLastIndex() + 1);
 172         } else {
 173
 174             // TODO: When we find that the follower is out of sync with the
 175             // Leader we simply decrement that followers next index by 1.
 176             // Would it be possible to do better than this? The RAFT spec
 177             // does not explicitly deal with it but may be something for us to
 178             // think about
 179
 180             followerLogInformation.decrNextIndex();
 181         }
 182
 183         // Now figure out if this reply warrants a change in the commitIndex
 184         // If there exists an N such that N > commitIndex, a majority
 185         // of matchIndex[i] ≥ N, and log[N].term == currentTerm:
 186         // set commitIndex = N (§5.3, §5.4).
 187         for (long N = context.getCommitIndex() + 1; ; N++) {
 188             int replicatedCount = 1;
 189
 190             for (FollowerLogInformation info : followerToLog.values()) {
 191                 if (info.getMatchIndex().get() >= N) {
 192                     replicatedCount++;
 193                 }
 194             }
 195
 196             if (replicatedCount >= minReplicationCount) {
 197                 ReplicatedLogEntry replicatedLogEntry = context.getReplicatedLog().get(N);
 198                 if (replicatedLogEntry != null &&
 199                     replicatedLogEntry.getTerm() == currentTerm()) {
 200                     context.setCommitIndex(N);
 201                 }
 202             } else {
 203                 break;
 204             }
 205         }
 206
 207         // Apply the change to the state machine
 208         if (context.getCommitIndex() > context.getLastApplied()) {
 209             applyLogToStateMachine(context.getCommitIndex());
 210         }
 211
 212         return this;
 213     }
 214
 215     protected ClientRequestTracker removeClientRequestTracker(long logIndex) {
 216
 217         ClientRequestTracker toRemove = findClientRequestTracker(logIndex);
 218         if(toRemove != null) {
 219             trackerList.remove(toRemove);
 220         }
 221
 222         return toRemove;
 223     }
 224
 225     protected ClientRequestTracker findClientRequestTracker(long logIndex) {
 226         for (ClientRequestTracker tracker : trackerList) {
 227             if (tracker.getIndex() == logIndex) {
 228                 return tracker;
 229             }
 230         }
 231         return null;
 232     }
 233
 234     @Override
 235     protected RaftActorBehavior handleRequestVoteReply(ActorRef sender,
 236         RequestVoteReply requestVoteReply) {
 237         return this;
 238     }
 239
 240     @Override
 241     public RaftState state() {
 242         return RaftState.Leader;
 243     }
 244
 245     @Override
 246     public RaftActorBehavior handleMessage(ActorRef sender, Object originalMessage) {
 247         Preconditions.checkNotNull(sender, "sender should not be null");
 248
 249         Object message = fromSerializableMessage(originalMessage);
 250
 251         if (message instanceof RaftRPC) {
 252             RaftRPC rpc = (RaftRPC) message;
 253             // If RPC request or response contains term T > currentTerm:
 254             // set currentTerm = T, convert to follower (§5.1)
 255             // This applies to all RPC messages and responses
 256             if (rpc.getTerm() > context.getTermInformation().getCurrentTerm()) {
 257                 context.getTermInformation().updateAndPersist(rpc.getTerm(), null);
 258
 259                 return switchBehavior(new Follower(context));
 260             }
 261         }
 262
 263         try {
 264             if (message instanceof SendHeartBeat) {
 265                 sendHeartBeat();
 266                 return this;
 267
 268             } else if(message instanceof InitiateInstallSnapshot) {
 269                 installSnapshotIfNeeded();
 270
 271             } else if(message instanceof SendInstallSnapshot) {
 272                 // received from RaftActor
 273                 setSnapshot(Optional.of(((SendInstallSnapshot) message).getSnapshot()));
 274                 sendInstallSnapshot();
 275
 276             } else if (message instanceof Replicate) {
 277                 replicate((Replicate) message);
 278
 279             } else if (message instanceof InstallSnapshotReply){
 280                 handleInstallSnapshotReply((InstallSnapshotReply) message);
 281
 282             }
 283         } finally {
 284             scheduleHeartBeat(context.getConfigParams().getHeartBeatInterval());
 285         }
 286
 287         return super.handleMessage(sender, message);
 288     }
 289
 290     private void handleInstallSnapshotReply(InstallSnapshotReply reply) {
 291         String followerId = reply.getFollowerId();
 292         FollowerToSnapshot followerToSnapshot = mapFollowerToSnapshot.get(followerId);
 293         FollowerLogInformation followerLogInformation = followerToLog.get(followerId);
 294         followerLogInformation.markFollowerActive();
 295
 296         if (followerToSnapshot != null &&
 297             followerToSnapshot.getChunkIndex() == reply.getChunkIndex()) {
 298
 299             if (reply.isSuccess()) {
 300                 if(followerToSnapshot.isLastChunk(reply.getChunkIndex())) {
 301                     //this was the last chunk reply
 302                     if(LOG.isDebugEnabled()) {
 303                         LOG.debug("InstallSnapshotReply received, " +
 304                                 "last chunk received, Chunk:{}. Follower:{} Setting nextIndex:{}",
 305                             reply.getChunkIndex(), followerId,
 306                             context.getReplicatedLog().getSnapshotIndex() + 1
 307                         );
 308                     }
 309
 310                     followerLogInformation.setMatchIndex(
 311                         context.getReplicatedLog().getSnapshotIndex());
 312                     followerLogInformation.setNextIndex(
 313                         context.getReplicatedLog().getSnapshotIndex() + 1);
 314                     mapFollowerToSnapshot.remove(followerId);
 315
 316                     if(LOG.isDebugEnabled()) {
 317                         LOG.debug("followerToLog.get(followerId).getNextIndex().get()=" +
 318                             followerToLog.get(followerId).getNextIndex().get());
 319                     }
 320
 321                     if (mapFollowerToSnapshot.isEmpty()) {
 322                         // once there are no pending followers receiving snapshots
 323                         // we can remove snapshot from the memory
 324                         setSnapshot(Optional.<ByteString>absent());
 325                     }
 326
 327                 } else {
 328                     followerToSnapshot.markSendStatus(true);
 329                 }
 330             } else {
 331                 LOG.info("InstallSnapshotReply received, " +
 332                         "sending snapshot chunk failed, Will retry, Chunk:{}",
 333                     reply.getChunkIndex()
 334                 );
 335                 followerToSnapshot.markSendStatus(false);
 336             }
 337
 338         } else {
 339             LOG.error("ERROR!!" +
 340                     "FollowerId in InstallSnapshotReply not known to Leader" +
 341                     " or Chunk Index in InstallSnapshotReply not matching {} != {}",
 342                 followerToSnapshot.getChunkIndex(), reply.getChunkIndex()
 343             );
 344         }
 345     }
 346
 347     private void replicate(Replicate replicate) {
 348         long logIndex = replicate.getReplicatedLogEntry().getIndex();
 349
 350         if(LOG.isDebugEnabled()) {
 351             LOG.debug("Replicate message {}", logIndex);
 352         }
 353
 354         // Create a tracker entry we will use this later to notify the
 355         // client actor
 356         trackerList.add(
 357             new ClientRequestTrackerImpl(replicate.getClientActor(),
 358                 replicate.getIdentifier(),
 359                 logIndex)
 360         );
 361
 362         if (followers.size() == 0) {
 363             context.setCommitIndex(logIndex);
 364             applyLogToStateMachine(logIndex);
 365         } else {
 366             sendAppendEntries();
 367         }
 368     }
 369
 370     private void sendAppendEntries() {
 371         // Send an AppendEntries to all followers
 372         for (String followerId : followers) {
 373             ActorSelection followerActor = context.getPeerActorSelection(followerId);
 374
 375             if (followerActor != null) {
 376                 FollowerLogInformation followerLogInformation = followerToLog.get(followerId);
 377                 long followerNextIndex = followerLogInformation.getNextIndex().get();
 378                 boolean isFollowerActive = followerLogInformation.isFollowerActive();
 379                 List<ReplicatedLogEntry> entries = null;
 380
 381                 if (mapFollowerToSnapshot.get(followerId) != null) {
 382                     // if install snapshot is in process , then sent next chunk if possible
 383                     if (isFollowerActive && mapFollowerToSnapshot.get(followerId).canSendNextChunk()) {
 384                         sendSnapshotChunk(followerActor, followerId);
 385                     } else {
 386                         // we send a heartbeat even if we have not received a reply for the last chunk
 387                         sendAppendEntriesToFollower(followerActor, followerNextIndex,
 388                             Collections.<ReplicatedLogEntry>emptyList());
 389                     }
 390
 391                 } else {
 392                     long leaderLastIndex = context.getReplicatedLog().lastIndex();
 393                     long leaderSnapShotIndex = context.getReplicatedLog().getSnapshotIndex();
 394
 395                     if (isFollowerActive &&
 396                         context.getReplicatedLog().isPresent(followerNextIndex)) {
 397                         // FIXME : Sending one entry at a time
 398                         entries = context.getReplicatedLog().getFrom(followerNextIndex, 1);
 399
 400                     } else if (isFollowerActive && followerNextIndex >= 0 &&
 401                         leaderLastIndex >= followerNextIndex ) {
 402                         // if the followers next index is not present in the leaders log, and
 403                         // if the follower is just not starting and if leader's index is more than followers index
 404                         // then snapshot should be sent
 405
 406                         if(LOG.isDebugEnabled()) {
 407                             LOG.debug("InitiateInstallSnapshot to follower:{}," +
 408                                     "follower-nextIndex:{}, leader-snapshot-index:{},  " +
 409                                     "leader-last-index:{}", followerId,
 410                                 followerNextIndex, leaderSnapShotIndex, leaderLastIndex
 411                             );
 412                         }
 413                         actor().tell(new InitiateInstallSnapshot(), actor());
 414
 415                         // we would want to sent AE as the capture snapshot might take time
 416                         entries =  Collections.<ReplicatedLogEntry>emptyList();
 417
 418                     } else {
 419                         //we send an AppendEntries, even if the follower is inactive
 420                         // in-order to update the followers timestamp, in case it becomes active again
 421                         entries =  Collections.<ReplicatedLogEntry>emptyList();
 422                     }
 423
 424                     sendAppendEntriesToFollower(followerActor, followerNextIndex, entries);
 425
 426                 }
 427             }
 428         }
 429     }
 430
 431     private void sendAppendEntriesToFollower(ActorSelection followerActor, long followerNextIndex,
 432         List<ReplicatedLogEntry> entries) {
 433         followerActor.tell(
 434             new AppendEntries(currentTerm(), context.getId(),
 435                 prevLogIndex(followerNextIndex),
 436                 prevLogTerm(followerNextIndex), entries,
 437                 context.getCommitIndex()).toSerializable(),
 438             actor()
 439         );
 440     }
 441
 442     /**
 443      * An installSnapshot is scheduled at a interval that is a multiple of
 444      * a HEARTBEAT_INTERVAL. This is to avoid the need to check for installing
 445      * snapshots at every heartbeat.
 446      *
 447      * Install Snapshot works as follows
 448      * 1. Leader sends a InitiateInstallSnapshot message to self
 449      * 2. Leader then initiates the capture snapshot by sending a CaptureSnapshot message to actor
 450      * 3. RaftActor on receipt of the CaptureSnapshotReply (from Shard), stores the received snapshot in the replicated log
 451      * and makes a call to Leader's handleMessage , with SendInstallSnapshot message.
 452      * 4. Leader , picks the snapshot from im-mem ReplicatedLog and sends it in chunks to the Follower
 453      * 5. On complete, Follower sends back a InstallSnapshotReply.
 454      * 6. On receipt of the InstallSnapshotReply for the last chunk, Leader marks the install complete for that follower
 455      * and replenishes the memory by deleting the snapshot in Replicated log.
 456      *
 457      */
 458     private void installSnapshotIfNeeded() {
 459         for (String followerId : followers) {
 460             ActorSelection followerActor =
 461                 context.getPeerActorSelection(followerId);
 462
 463             if(followerActor != null) {
 464                 FollowerLogInformation followerLogInformation =
 465                     followerToLog.get(followerId);
 466
 467                 long nextIndex = followerLogInformation.getNextIndex().get();
 468
 469                 if (!context.getReplicatedLog().isPresent(nextIndex) &&
 470                     context.getReplicatedLog().isInSnapshot(nextIndex)) {
 471                     LOG.info("{} follower needs a snapshot install", followerId);
 472                     if (snapshot.isPresent()) {
 473                         // if a snapshot is present in the memory, most likely another install is in progress
 474                         // no need to capture snapshot
 475                         sendSnapshotChunk(followerActor, followerId);
 476
 477                     } else {
 478                         initiateCaptureSnapshot();
 479                         //we just need 1 follower who would need snapshot to be installed.
 480                         // when we have the snapshot captured, we would again check (in SendInstallSnapshot)
 481                         // who needs an install and send to all who need
 482                         break;
 483                     }
 484
 485                 }
 486             }
 487         }
 488     }
 489
 490     // on every install snapshot, we try to capture the snapshot.
 491     // Once a capture is going on, another one issued will get ignored by RaftActor.
 492     private void initiateCaptureSnapshot() {
 493         LOG.info("Initiating Snapshot Capture to Install Snapshot, Leader:{}", getLeaderId());
 494         ReplicatedLogEntry lastAppliedEntry = context.getReplicatedLog().get(context.getLastApplied());
 495         long lastAppliedIndex = -1;
 496         long lastAppliedTerm = -1;
 497
 498         if (lastAppliedEntry != null) {
 499             lastAppliedIndex = lastAppliedEntry.getIndex();
 500             lastAppliedTerm = lastAppliedEntry.getTerm();
 501         } else if (context.getReplicatedLog().getSnapshotIndex() > -1)  {
 502             lastAppliedIndex = context.getReplicatedLog().getSnapshotIndex();
 503             lastAppliedTerm = context.getReplicatedLog().getSnapshotTerm();
 504         }
 505
 506         boolean isInstallSnapshotInitiated = true;
 507         actor().tell(new CaptureSnapshot(lastIndex(), lastTerm(),
 508                 lastAppliedIndex, lastAppliedTerm, isInstallSnapshotInitiated),
 509             actor());
 510     }
 511
 512
 513     private void sendInstallSnapshot() {
 514         for (String followerId : followers) {
 515             ActorSelection followerActor = context.getPeerActorSelection(followerId);
 516
 517             if(followerActor != null) {
 518                 FollowerLogInformation followerLogInformation = followerToLog.get(followerId);
 519                 long nextIndex = followerLogInformation.getNextIndex().get();
 520
 521                 if (!context.getReplicatedLog().isPresent(nextIndex) &&
 522                     context.getReplicatedLog().isInSnapshot(nextIndex)) {
 523                     sendSnapshotChunk(followerActor, followerId);
 524                 }
 525             }
 526         }
 527     }
 528
 529     /**
 530      *  Sends a snapshot chunk to a given follower
 531      *  InstallSnapshot should qualify as a heartbeat too.
 532      */
 533     private void sendSnapshotChunk(ActorSelection followerActor, String followerId) {
 534         try {
 535             if (snapshot.isPresent()) {
 536                 followerActor.tell(
 537                     new InstallSnapshot(currentTerm(), context.getId(),
 538                         context.getReplicatedLog().getSnapshotIndex(),
 539                         context.getReplicatedLog().getSnapshotTerm(),
 540                         getNextSnapshotChunk(followerId,snapshot.get()),
 541                         mapFollowerToSnapshot.get(followerId).incrementChunkIndex(),
 542                         mapFollowerToSnapshot.get(followerId).getTotalChunks()
 543                     ).toSerializable(),
 544                     actor()
 545                 );
 546                 LOG.info("InstallSnapshot sent to follower {}, Chunk: {}/{}",
 547                     followerActor.path(), mapFollowerToSnapshot.get(followerId).getChunkIndex(),
 548                     mapFollowerToSnapshot.get(followerId).getTotalChunks());
 549             }
 550         } catch (IOException e) {
 551             LOG.error(e, "InstallSnapshot failed for Leader.");
 552         }
 553     }
 554
 555     /**
 556      * Acccepts snaphot as ByteString, enters into map for future chunks
 557      * creates and return a ByteString chunk
 558      */
 559     private ByteString getNextSnapshotChunk(String followerId, ByteString snapshotBytes) throws IOException {
 560         FollowerToSnapshot followerToSnapshot = mapFollowerToSnapshot.get(followerId);
 561         if (followerToSnapshot == null) {
 562             followerToSnapshot = new FollowerToSnapshot(snapshotBytes);
 563             mapFollowerToSnapshot.put(followerId, followerToSnapshot);
 564         }
 565         ByteString nextChunk = followerToSnapshot.getNextChunk();
 566         if (LOG.isDebugEnabled()) {
 567             LOG.debug("Leader's snapshot nextChunk size:{}", nextChunk.size());
 568         }
 569         return nextChunk;
 570     }
 571
 572     private void sendHeartBeat() {
 573         if (followers.size() > 0) {
 574             sendAppendEntries();
 575         }
 576     }
 577
 578     private void stopHeartBeat() {
 579         if (heartbeatSchedule != null && !heartbeatSchedule.isCancelled()) {
 580             heartbeatSchedule.cancel();
 581         }
 582     }
 583
 584     private void scheduleHeartBeat(FiniteDuration interval) {
 585         if(followers.size() == 0){
 586             // Optimization - do not bother scheduling a heartbeat as there are
 587             // no followers
 588             return;
 589         }
 590
 591         stopHeartBeat();
 592
 593         // Schedule a heartbeat. When the scheduler triggers a SendHeartbeat
 594         // message is sent to itself.
 595         // Scheduling the heartbeat only once here because heartbeats do not
 596         // need to be sent if there are other messages being sent to the remote
 597         // actor.
 598         heartbeatSchedule = context.getActorSystem().scheduler().scheduleOnce(
 599             interval, context.getActor(), new SendHeartBeat(),
 600             context.getActorSystem().dispatcher(), context.getActor());
 601     }
 602
 603     @Override
 604     public void close() throws Exception {
 605         stopHeartBeat();
 606     }
 607
 608     @Override
 609     public String getLeaderId() {
 610         return context.getId();
 611     }
 612
 613     protected boolean isLeaderIsolated() {
 614         int minPresent = minIsolatedLeaderPeerCount;
 615         for (FollowerLogInformation followerLogInformation : followerToLog.values()) {
 616             if (followerLogInformation.isFollowerActive()) {
 617                 --minPresent;
 618                 if (minPresent == 0) {
 619                     break;
 620                 }
 621             }
 622         }
 623         return (minPresent != 0);
 624     }
 625
 626     /**
 627      * Encapsulates the snapshot bytestring and handles the logic of sending
 628      * snapshot chunks
 629      */
 630     protected class FollowerToSnapshot {
 631         private ByteString snapshotBytes;
 632         private int offset = 0;
 633         // the next snapshot chunk is sent only if the replyReceivedForOffset matches offset
 634         private int replyReceivedForOffset;
 635         // if replyStatus is false, the previous chunk is attempted
 636         private boolean replyStatus = false;
 637         private int chunkIndex;
 638         private int totalChunks;
 639
 640         public FollowerToSnapshot(ByteString snapshotBytes) {
 641             this.snapshotBytes = snapshotBytes;
 642             replyReceivedForOffset = -1;
 643             chunkIndex = 1;
 644             int size = snapshotBytes.size();
 645             totalChunks = ( size / context.getConfigParams().getSnapshotChunkSize()) +
 646                 ((size % context.getConfigParams().getSnapshotChunkSize()) > 0 ? 1 : 0);
 647             if(LOG.isDebugEnabled()) {
 648                 LOG.debug("Snapshot {} bytes, total chunks to send:{}",
 649                     size, totalChunks);
 650             }
 651         }
 652
 653         public ByteString getSnapshotBytes() {
 654             return snapshotBytes;
 655         }
 656
 657         public int incrementOffset() {
 658             if(replyStatus) {
 659                 // if prev chunk failed, we would want to sent the same chunk again
 660                 offset = offset + context.getConfigParams().getSnapshotChunkSize();
 661             }
 662             return offset;
 663         }
 664
 665         public int incrementChunkIndex() {
 666             if (replyStatus) {
 667                 // if prev chunk failed, we would want to sent the same chunk again
 668                 chunkIndex =  chunkIndex + 1;
 669             }
 670             return chunkIndex;
 671         }
 672
 673         public int getChunkIndex() {
 674             return chunkIndex;
 675         }
 676
 677         public int getTotalChunks() {
 678             return totalChunks;
 679         }
 680
 681         public boolean canSendNextChunk() {
 682             // we only send a false if a chunk is sent but we have not received a reply yet
 683             return replyReceivedForOffset == offset;
 684         }
 685
 686         public boolean isLastChunk(int chunkIndex) {
 687             return totalChunks == chunkIndex;
 688         }
 689
 690         public void markSendStatus(boolean success) {
 691             if (success) {
 692                 // if the chunk sent was successful
 693                 replyReceivedForOffset = offset;
 694                 replyStatus = true;
 695             } else {
 696                 // if the chunk sent was failure
 697                 replyReceivedForOffset = offset;
 698                 replyStatus = false;
 699             }
 700         }
 701
 702         public ByteString getNextChunk() {
 703             int snapshotLength = getSnapshotBytes().size();
 704             int start = incrementOffset();
 705             int size = context.getConfigParams().getSnapshotChunkSize();
 706             if (context.getConfigParams().getSnapshotChunkSize() > snapshotLength) {
 707                 size = snapshotLength;
 708             } else {
 709                 if ((start + context.getConfigParams().getSnapshotChunkSize()) > snapshotLength) {
 710                     size = snapshotLength - start;
 711                 }
 712             }
 713
 714             if(LOG.isDebugEnabled()) {
 715                 LOG.debug("length={}, offset={},size={}",
 716                     snapshotLength, start, size);
 717             }
 718             return getSnapshotBytes().substring(start, start + size);
 719
 720         }
 721     }
 722
 723     // called from example-actor for printing the follower-states
 724     public String printFollowerStates() {
 725         StringBuilder sb = new StringBuilder();
 726         for(FollowerLogInformation followerLogInformation : followerToLog.values()) {
 727             boolean isFollowerActive = followerLogInformation.isFollowerActive();
 728             sb.append("{"+followerLogInformation.getId() + " state:" + isFollowerActive + "},");
 729
 730         }
 731         return "[" + sb.toString() + "]";
 732     }
 733
 734     @VisibleForTesting
 735     void markFollowerActive(String followerId) {
 736         followerToLog.get(followerId).markFollowerActive();
 737     }
 738 }