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.common.collect.ImmutableMap;
  18 import com.google.common.collect.ImmutableMap.Builder;
  19 import com.google.protobuf.ByteString;
  20 import java.io.IOException;
  21 import java.util.Collection;
  22 import java.util.Collections;
  23 import java.util.HashMap;
  24 import java.util.Iterator;
  25 import java.util.LinkedList;
  26 import java.util.List;
  27 import java.util.Map;
  28 import java.util.Map.Entry;
  29 import java.util.concurrent.TimeUnit;
  30 import org.opendaylight.controller.cluster.raft.ClientRequestTracker;
  31 import org.opendaylight.controller.cluster.raft.ClientRequestTrackerImpl;
  32 import org.opendaylight.controller.cluster.raft.FollowerLogInformation;
  33 import org.opendaylight.controller.cluster.raft.FollowerLogInformationImpl;
  34 import org.opendaylight.controller.cluster.raft.RaftActorContext;
  35 import org.opendaylight.controller.cluster.raft.RaftState;
  36 import org.opendaylight.controller.cluster.raft.ReplicatedLogEntry;
  37 import org.opendaylight.controller.cluster.raft.base.messages.CaptureSnapshot;
  38 import org.opendaylight.controller.cluster.raft.base.messages.InitiateInstallSnapshot;
  39 import org.opendaylight.controller.cluster.raft.base.messages.Replicate;
  40 import org.opendaylight.controller.cluster.raft.base.messages.SendHeartBeat;
  41 import org.opendaylight.controller.cluster.raft.base.messages.SendInstallSnapshot;
  42 import org.opendaylight.controller.cluster.raft.messages.AppendEntries;
  43 import org.opendaylight.controller.cluster.raft.messages.AppendEntriesReply;
  44 import org.opendaylight.controller.cluster.raft.messages.InstallSnapshot;
  45 import org.opendaylight.controller.cluster.raft.messages.InstallSnapshotReply;
  46 import org.opendaylight.controller.cluster.raft.messages.RaftRPC;
  47 import org.opendaylight.controller.cluster.raft.messages.RequestVoteReply;
  48 import scala.concurrent.duration.FiniteDuration;
  49
  50 /**
  51  * The behavior of a RaftActor when it is in the Leader state
  52  * <p/>
  53  * Leaders:
  54  * <ul>
  55  * <li> Upon election: send initial empty AppendEntries RPCs
  56  * (heartbeat) to each server; repeat during idle periods to
  57  * prevent election timeouts (§5.2)
  58  * <li> If command received from client: append entry to local log,
  59  * respond after entry applied to state machine (§5.3)
  60  * <li> If last log index ≥ nextIndex for a follower: send
  61  * AppendEntries RPC with log entries starting at nextIndex
  62  * <ul>
  63  * <li> If successful: update nextIndex and matchIndex for
  64  * follower (§5.3)
  65  * <li> If AppendEntries fails because of log inconsistency:
  66  * decrement nextIndex and retry (§5.3)
  67  * </ul>
  68  * <li> If there exists an N such that N > commitIndex, a majority
  69  * of matchIndex[i] ≥ N, and log[N].term == currentTerm:
  70  * set commitIndex = N (§5.3, §5.4).
  71  */
  72 public abstract class AbstractLeader extends AbstractRaftActorBehavior {
  73
  74     // The index of the first chunk that is sent when installing a snapshot
  75     public static final int FIRST_CHUNK_INDEX = 1;
  76
  77     // The index that the follower should respond with if it needs the install snapshot to be reset
  78     public static final int INVALID_CHUNK_INDEX = -1;
  79
  80     // This would be passed as the hash code of the last chunk when sending the first chunk
  81     public static final int INITIAL_LAST_CHUNK_HASH_CODE = -1;
  82
  83     private final Map<String, FollowerLogInformation> followerToLog;
  84     private final Map<String, FollowerToSnapshot> mapFollowerToSnapshot = new HashMap<>();
  85
  86     private Cancellable heartbeatSchedule = null;
  87
  88     private final Collection<ClientRequestTracker> trackerList = new LinkedList<>();
  89
  90     protected final int minReplicationCount;
  91
  92     protected final int minIsolatedLeaderPeerCount;
  93
  94     private Optional<ByteString> snapshot;
  95
  96     public AbstractLeader(RaftActorContext context) {
  97         super(context);
  98
  99         final Builder<String, FollowerLogInformation> ftlBuilder = ImmutableMap.builder();
 100         for (String followerId : context.getPeerAddresses().keySet()) {
 101             FollowerLogInformation followerLogInformation =
 102                 new FollowerLogInformationImpl(followerId,
 103                     context.getCommitIndex(), -1,
 104                     context.getConfigParams().getElectionTimeOutInterval());
 105
 106             ftlBuilder.put(followerId, followerLogInformation);
 107         }
 108         followerToLog = ftlBuilder.build();
 109
 110         leaderId = context.getId();
 111
 112         LOG.debug("{}: Election: Leader has following peers: {}", context.getId(), getFollowerIds());
 113
 114         minReplicationCount = getMajorityVoteCount(getFollowerIds().size());
 115
 116         // the isolated Leader peer count will be 1 less than the majority vote count.
 117         // this is because the vote count has the self vote counted in it
 118         // for e.g
 119         // 0 peers = 1 votesRequired , minIsolatedLeaderPeerCount = 0
 120         // 2 peers = 2 votesRequired , minIsolatedLeaderPeerCount = 1
 121         // 4 peers = 3 votesRequired, minIsolatedLeaderPeerCount = 2
 122         minIsolatedLeaderPeerCount = minReplicationCount > 0 ? (minReplicationCount - 1) : 0;
 123
 124         snapshot = Optional.absent();
 125
 126         // Immediately schedule a heartbeat
 127         // Upon election: send initial empty AppendEntries RPCs
 128         // (heartbeat) to each server; repeat during idle periods to
 129         // prevent election timeouts (§5.2)
 130         scheduleHeartBeat(new FiniteDuration(0, TimeUnit.SECONDS));
 131     }
 132
 133     /**
 134      * Return an immutable collection of follower identifiers.
 135      *
 136      * @return Collection of follower IDs
 137      */
 138     protected final Collection<String> getFollowerIds() {
 139         return followerToLog.keySet();
 140     }
 141
 142     private Optional<ByteString> getSnapshot() {
 143         return snapshot;
 144     }
 145
 146     @VisibleForTesting
 147     void setSnapshot(Optional<ByteString> snapshot) {
 148         this.snapshot = snapshot;
 149     }
 150
 151     @Override
 152     protected RaftActorBehavior handleAppendEntries(ActorRef sender,
 153         AppendEntries appendEntries) {
 154
 155         if(LOG.isDebugEnabled()) {
 156             LOG.debug("{}: handleAppendEntries: {}", context.getId(), appendEntries);
 157         }
 158
 159         return this;
 160     }
 161
 162     @Override
 163     protected RaftActorBehavior handleAppendEntriesReply(ActorRef sender,
 164         AppendEntriesReply appendEntriesReply) {
 165
 166         if(! appendEntriesReply.isSuccess()) {
 167             if(LOG.isDebugEnabled()) {
 168                 LOG.debug("{}: handleAppendEntriesReply: {}", context.getId(), appendEntriesReply);
 169             }
 170         }
 171
 172         // Update the FollowerLogInformation
 173         String followerId = appendEntriesReply.getFollowerId();
 174         FollowerLogInformation followerLogInformation =
 175             followerToLog.get(followerId);
 176
 177         if(followerLogInformation == null){
 178             LOG.error("{}: handleAppendEntriesReply - unknown follower {}", context.getId(), followerId);
 179             return this;
 180         }
 181
 182         followerLogInformation.markFollowerActive();
 183
 184         if (appendEntriesReply.isSuccess()) {
 185             followerLogInformation
 186                 .setMatchIndex(appendEntriesReply.getLogLastIndex());
 187             followerLogInformation
 188                 .setNextIndex(appendEntriesReply.getLogLastIndex() + 1);
 189         } else {
 190
 191             // TODO: When we find that the follower is out of sync with the
 192             // Leader we simply decrement that followers next index by 1.
 193             // Would it be possible to do better than this? The RAFT spec
 194             // does not explicitly deal with it but may be something for us to
 195             // think about
 196
 197             followerLogInformation.decrNextIndex();
 198         }
 199
 200         // Now figure out if this reply warrants a change in the commitIndex
 201         // If there exists an N such that N > commitIndex, a majority
 202         // of matchIndex[i] ≥ N, and log[N].term == currentTerm:
 203         // set commitIndex = N (§5.3, §5.4).
 204         for (long N = context.getCommitIndex() + 1; ; N++) {
 205             int replicatedCount = 1;
 206
 207             for (FollowerLogInformation info : followerToLog.values()) {
 208                 if (info.getMatchIndex() >= N) {
 209                     replicatedCount++;
 210                 }
 211             }
 212
 213             if (replicatedCount >= minReplicationCount) {
 214                 ReplicatedLogEntry replicatedLogEntry = context.getReplicatedLog().get(N);
 215                 if (replicatedLogEntry != null &&
 216                     replicatedLogEntry.getTerm() == currentTerm()) {
 217                     context.setCommitIndex(N);
 218                 }
 219             } else {
 220                 break;
 221             }
 222         }
 223
 224         // Apply the change to the state machine
 225         if (context.getCommitIndex() > context.getLastApplied()) {
 226             applyLogToStateMachine(context.getCommitIndex());
 227         }
 228
 229         return this;
 230     }
 231
 232     @Override
 233     protected ClientRequestTracker removeClientRequestTracker(long logIndex) {
 234         final Iterator<ClientRequestTracker> it = trackerList.iterator();
 235         while (it.hasNext()) {
 236             final ClientRequestTracker t = it.next();
 237             if (t.getIndex() == logIndex) {
 238                 it.remove();
 239                 return t;
 240             }
 241         }
 242
 243         return null;
 244     }
 245
 246     @Override
 247     protected ClientRequestTracker findClientRequestTracker(long logIndex) {
 248         for (ClientRequestTracker tracker : trackerList) {
 249             if (tracker.getIndex() == logIndex) {
 250                 return tracker;
 251             }
 252         }
 253         return null;
 254     }
 255
 256     @Override
 257     protected RaftActorBehavior handleRequestVoteReply(ActorRef sender,
 258         RequestVoteReply requestVoteReply) {
 259         return this;
 260     }
 261
 262     @Override
 263     public RaftState state() {
 264         return RaftState.Leader;
 265     }
 266
 267     @Override
 268     public RaftActorBehavior handleMessage(ActorRef sender, Object originalMessage) {
 269         Preconditions.checkNotNull(sender, "sender should not be null");
 270
 271         Object message = fromSerializableMessage(originalMessage);
 272
 273         if (message instanceof RaftRPC) {
 274             RaftRPC rpc = (RaftRPC) message;
 275             // If RPC request or response contains term T > currentTerm:
 276             // set currentTerm = T, convert to follower (§5.1)
 277             // This applies to all RPC messages and responses
 278             if (rpc.getTerm() > context.getTermInformation().getCurrentTerm()) {
 279                 context.getTermInformation().updateAndPersist(rpc.getTerm(), null);
 280
 281                 return switchBehavior(new Follower(context));
 282             }
 283         }
 284
 285         try {
 286             if (message instanceof SendHeartBeat) {
 287                 sendHeartBeat();
 288                 return this;
 289
 290             } else if(message instanceof InitiateInstallSnapshot) {
 291                 installSnapshotIfNeeded();
 292
 293             } else if(message instanceof SendInstallSnapshot) {
 294                 // received from RaftActor
 295                 setSnapshot(Optional.of(((SendInstallSnapshot) message).getSnapshot()));
 296                 sendInstallSnapshot();
 297
 298             } else if (message instanceof Replicate) {
 299                 replicate((Replicate) message);
 300
 301             } else if (message instanceof InstallSnapshotReply){
 302                 handleInstallSnapshotReply((InstallSnapshotReply) message);
 303
 304             }
 305         } finally {
 306             scheduleHeartBeat(context.getConfigParams().getHeartBeatInterval());
 307         }
 308
 309         return super.handleMessage(sender, message);
 310     }
 311
 312     private void handleInstallSnapshotReply(InstallSnapshotReply reply) {
 313         String followerId = reply.getFollowerId();
 314         FollowerToSnapshot followerToSnapshot = mapFollowerToSnapshot.get(followerId);
 315         FollowerLogInformation followerLogInformation = followerToLog.get(followerId);
 316         followerLogInformation.markFollowerActive();
 317
 318         if (followerToSnapshot != null &&
 319             followerToSnapshot.getChunkIndex() == reply.getChunkIndex()) {
 320
 321             if (reply.isSuccess()) {
 322                 if(followerToSnapshot.isLastChunk(reply.getChunkIndex())) {
 323                     //this was the last chunk reply
 324                     if(LOG.isDebugEnabled()) {
 325                         LOG.debug("{}: InstallSnapshotReply received, " +
 326                                 "last chunk received, Chunk:{}. Follower:{} Setting nextIndex:{}",
 327                                 context.getId(), reply.getChunkIndex(), followerId,
 328                             context.getReplicatedLog().getSnapshotIndex() + 1
 329                         );
 330                     }
 331
 332                     followerLogInformation.setMatchIndex(
 333                         context.getReplicatedLog().getSnapshotIndex());
 334                     followerLogInformation.setNextIndex(
 335                         context.getReplicatedLog().getSnapshotIndex() + 1);
 336                     mapFollowerToSnapshot.remove(followerId);
 337
 338                     if(LOG.isDebugEnabled()) {
 339                         LOG.debug("{}: followerToLog.get(followerId).getNextIndex()=" +
 340                                 context.getId(), followerToLog.get(followerId).getNextIndex());
 341                     }
 342
 343                     if (mapFollowerToSnapshot.isEmpty()) {
 344                         // once there are no pending followers receiving snapshots
 345                         // we can remove snapshot from the memory
 346                         setSnapshot(Optional.<ByteString>absent());
 347                     }
 348
 349                 } else {
 350                     followerToSnapshot.markSendStatus(true);
 351                 }
 352             } else {
 353                 LOG.info("{}: InstallSnapshotReply received sending snapshot chunk failed, Will retry, Chunk: {}",
 354                         context.getId(), reply.getChunkIndex());
 355
 356                 followerToSnapshot.markSendStatus(false);
 357             }
 358
 359         } else {
 360             LOG.error("{}: FollowerId in InstallSnapshotReply not known to Leader" +
 361                     " or Chunk Index in InstallSnapshotReply not matching {} != {}",
 362                     context.getId(), followerToSnapshot.getChunkIndex(), reply.getChunkIndex()
 363             );
 364
 365             if(reply.getChunkIndex() == INVALID_CHUNK_INDEX){
 366                 // Since the Follower did not find this index to be valid we should reset the follower snapshot
 367                 // so that Installing the snapshot can resume from the beginning
 368                 followerToSnapshot.reset();
 369             }
 370         }
 371     }
 372
 373     private void replicate(Replicate replicate) {
 374         long logIndex = replicate.getReplicatedLogEntry().getIndex();
 375
 376         if(LOG.isDebugEnabled()) {
 377             LOG.debug("{}: Replicate message {}", context.getId(), logIndex);
 378         }
 379
 380         // Create a tracker entry we will use this later to notify the
 381         // client actor
 382         trackerList.add(
 383             new ClientRequestTrackerImpl(replicate.getClientActor(),
 384                 replicate.getIdentifier(),
 385                 logIndex)
 386         );
 387
 388         if (followerToLog.isEmpty()) {
 389             context.setCommitIndex(logIndex);
 390             applyLogToStateMachine(logIndex);
 391         } else {
 392             sendAppendEntries();
 393         }
 394     }
 395
 396     private void sendAppendEntries() {
 397         // Send an AppendEntries to all followers
 398         for (Entry<String, FollowerLogInformation> e : followerToLog.entrySet()) {
 399             final String followerId = e.getKey();
 400             ActorSelection followerActor = context.getPeerActorSelection(followerId);
 401
 402             if (followerActor != null) {
 403                 FollowerLogInformation followerLogInformation = followerToLog.get(followerId);
 404                 long followerNextIndex = followerLogInformation.getNextIndex();
 405                 boolean isFollowerActive = followerLogInformation.isFollowerActive();
 406
 407                 if (mapFollowerToSnapshot.get(followerId) != null) {
 408                     // if install snapshot is in process , then sent next chunk if possible
 409                     if (isFollowerActive && mapFollowerToSnapshot.get(followerId).canSendNextChunk()) {
 410                         sendSnapshotChunk(followerActor, followerId);
 411                     } else {
 412                         // we send a heartbeat even if we have not received a reply for the last chunk
 413                         sendAppendEntriesToFollower(followerActor, followerNextIndex,
 414                             Collections.<ReplicatedLogEntry>emptyList());
 415                     }
 416
 417                 } else {
 418                     long leaderLastIndex = context.getReplicatedLog().lastIndex();
 419                     long leaderSnapShotIndex = context.getReplicatedLog().getSnapshotIndex();
 420                     final List<ReplicatedLogEntry> entries;
 421
 422                     if (isFollowerActive &&
 423                         context.getReplicatedLog().isPresent(followerNextIndex)) {
 424                         // FIXME : Sending one entry at a time
 425                         entries = context.getReplicatedLog().getFrom(followerNextIndex, 1);
 426
 427                     } else if (isFollowerActive && followerNextIndex >= 0 &&
 428                         leaderLastIndex >= followerNextIndex ) {
 429                         // if the followers next index is not present in the leaders log, and
 430                         // if the follower is just not starting and if leader's index is more than followers index
 431                         // then snapshot should be sent
 432
 433                         if(LOG.isDebugEnabled()) {
 434                             LOG.debug(String.format("%s: InitiateInstallSnapshot to follower: %s," +
 435                                     "follower-nextIndex: %s, leader-snapshot-index: %s,  " +
 436                                     "leader-last-index: %s", context.getId(), followerId,
 437                                 followerNextIndex, leaderSnapShotIndex, leaderLastIndex));
 438                         }
 439                         actor().tell(new InitiateInstallSnapshot(), actor());
 440
 441                         // we would want to sent AE as the capture snapshot might take time
 442                         entries =  Collections.<ReplicatedLogEntry>emptyList();
 443
 444                     } else {
 445                         //we send an AppendEntries, even if the follower is inactive
 446                         // in-order to update the followers timestamp, in case it becomes active again
 447                         entries =  Collections.<ReplicatedLogEntry>emptyList();
 448                     }
 449
 450                     sendAppendEntriesToFollower(followerActor, followerNextIndex, entries);
 451
 452                 }
 453             }
 454         }
 455     }
 456
 457     private void sendAppendEntriesToFollower(ActorSelection followerActor, long followerNextIndex,
 458         List<ReplicatedLogEntry> entries) {
 459         followerActor.tell(
 460             new AppendEntries(currentTerm(), context.getId(),
 461                 prevLogIndex(followerNextIndex),
 462                 prevLogTerm(followerNextIndex), entries,
 463                 context.getCommitIndex()).toSerializable(),
 464             actor()
 465         );
 466     }
 467
 468     /**
 469      * An installSnapshot is scheduled at a interval that is a multiple of
 470      * a HEARTBEAT_INTERVAL. This is to avoid the need to check for installing
 471      * snapshots at every heartbeat.
 472      *
 473      * Install Snapshot works as follows
 474      * 1. Leader sends a InitiateInstallSnapshot message to self
 475      * 2. Leader then initiates the capture snapshot by sending a CaptureSnapshot message to actor
 476      * 3. RaftActor on receipt of the CaptureSnapshotReply (from Shard), stores the received snapshot in the replicated log
 477      * and makes a call to Leader's handleMessage , with SendInstallSnapshot message.
 478      * 4. Leader , picks the snapshot from im-mem ReplicatedLog and sends it in chunks to the Follower
 479      * 5. On complete, Follower sends back a InstallSnapshotReply.
 480      * 6. On receipt of the InstallSnapshotReply for the last chunk, Leader marks the install complete for that follower
 481      * and replenishes the memory by deleting the snapshot in Replicated log.
 482      *
 483      */
 484     private void installSnapshotIfNeeded() {
 485         for (Entry<String, FollowerLogInformation> e : followerToLog.entrySet()) {
 486             final ActorSelection followerActor = context.getPeerActorSelection(e.getKey());
 487
 488             if (followerActor != null) {
 489                 long nextIndex = e.getValue().getNextIndex();
 490
 491                 if (!context.getReplicatedLog().isPresent(nextIndex) &&
 492                     context.getReplicatedLog().isInSnapshot(nextIndex)) {
 493                     LOG.info("{}: {} follower needs a snapshot install", context.getId(), e.getKey());
 494                     if (snapshot.isPresent()) {
 495                         // if a snapshot is present in the memory, most likely another install is in progress
 496                         // no need to capture snapshot
 497                         sendSnapshotChunk(followerActor, e.getKey());
 498
 499                     } else {
 500                         initiateCaptureSnapshot();
 501                         //we just need 1 follower who would need snapshot to be installed.
 502                         // when we have the snapshot captured, we would again check (in SendInstallSnapshot)
 503                         // who needs an install and send to all who need
 504                         break;
 505                     }
 506
 507                 }
 508             }
 509         }
 510     }
 511
 512     // on every install snapshot, we try to capture the snapshot.
 513     // Once a capture is going on, another one issued will get ignored by RaftActor.
 514     private void initiateCaptureSnapshot() {
 515         LOG.info("{}: Initiating Snapshot Capture to Install Snapshot, Leader:{}", context.getId(), getLeaderId());
 516         ReplicatedLogEntry lastAppliedEntry = context.getReplicatedLog().get(context.getLastApplied());
 517         long lastAppliedIndex = -1;
 518         long lastAppliedTerm = -1;
 519
 520         if (lastAppliedEntry != null) {
 521             lastAppliedIndex = lastAppliedEntry.getIndex();
 522             lastAppliedTerm = lastAppliedEntry.getTerm();
 523         } else if (context.getReplicatedLog().getSnapshotIndex() > -1)  {
 524             lastAppliedIndex = context.getReplicatedLog().getSnapshotIndex();
 525             lastAppliedTerm = context.getReplicatedLog().getSnapshotTerm();
 526         }
 527
 528         boolean isInstallSnapshotInitiated = true;
 529         actor().tell(new CaptureSnapshot(lastIndex(), lastTerm(),
 530                 lastAppliedIndex, lastAppliedTerm, isInstallSnapshotInitiated),
 531             actor());
 532     }
 533
 534
 535     private void sendInstallSnapshot() {
 536         for (Entry<String, FollowerLogInformation> e : followerToLog.entrySet()) {
 537             ActorSelection followerActor = context.getPeerActorSelection(e.getKey());
 538
 539             if (followerActor != null) {
 540                 long nextIndex = e.getValue().getNextIndex();
 541
 542                 if (!context.getReplicatedLog().isPresent(nextIndex) &&
 543                     context.getReplicatedLog().isInSnapshot(nextIndex)) {
 544                     sendSnapshotChunk(followerActor, e.getKey());
 545                 }
 546             }
 547         }
 548     }
 549
 550     /**
 551      *  Sends a snapshot chunk to a given follower
 552      *  InstallSnapshot should qualify as a heartbeat too.
 553      */
 554     private void sendSnapshotChunk(ActorSelection followerActor, String followerId) {
 555         try {
 556             if (snapshot.isPresent()) {
 557                 followerActor.tell(
 558                     new InstallSnapshot(currentTerm(), context.getId(),
 559                         context.getReplicatedLog().getSnapshotIndex(),
 560                         context.getReplicatedLog().getSnapshotTerm(),
 561                         getNextSnapshotChunk(followerId,snapshot.get()),
 562                         mapFollowerToSnapshot.get(followerId).incrementChunkIndex(),
 563                         mapFollowerToSnapshot.get(followerId).getTotalChunks(),
 564                         Optional.of(mapFollowerToSnapshot.get(followerId).getLastChunkHashCode())
 565                     ).toSerializable(),
 566                     actor()
 567                 );
 568                 LOG.info("{}: InstallSnapshot sent to follower {}, Chunk: {}/{}",
 569                         context.getId(), followerActor.path(),
 570                         mapFollowerToSnapshot.get(followerId).getChunkIndex(),
 571                         mapFollowerToSnapshot.get(followerId).getTotalChunks());
 572             }
 573         } catch (IOException e) {
 574             LOG.error(e, "{}: InstallSnapshot failed for Leader.", context.getId());
 575         }
 576     }
 577
 578     /**
 579      * Acccepts snaphot as ByteString, enters into map for future chunks
 580      * creates and return a ByteString chunk
 581      */
 582     private ByteString getNextSnapshotChunk(String followerId, ByteString snapshotBytes) throws IOException {
 583         FollowerToSnapshot followerToSnapshot = mapFollowerToSnapshot.get(followerId);
 584         if (followerToSnapshot == null) {
 585             followerToSnapshot = new FollowerToSnapshot(snapshotBytes);
 586             mapFollowerToSnapshot.put(followerId, followerToSnapshot);
 587         }
 588         ByteString nextChunk = followerToSnapshot.getNextChunk();
 589         if (LOG.isDebugEnabled()) {
 590             LOG.debug("{}: Leader's snapshot nextChunk size:{}", context.getId(), nextChunk.size());
 591         }
 592         return nextChunk;
 593     }
 594
 595     private void sendHeartBeat() {
 596         if (!followerToLog.isEmpty()) {
 597             sendAppendEntries();
 598         }
 599     }
 600
 601     private void stopHeartBeat() {
 602         if (heartbeatSchedule != null && !heartbeatSchedule.isCancelled()) {
 603             heartbeatSchedule.cancel();
 604         }
 605     }
 606
 607     private void scheduleHeartBeat(FiniteDuration interval) {
 608         if (followerToLog.isEmpty()) {
 609             // Optimization - do not bother scheduling a heartbeat as there are
 610             // no followers
 611             return;
 612         }
 613
 614         stopHeartBeat();
 615
 616         // Schedule a heartbeat. When the scheduler triggers a SendHeartbeat
 617         // message is sent to itself.
 618         // Scheduling the heartbeat only once here because heartbeats do not
 619         // need to be sent if there are other messages being sent to the remote
 620         // actor.
 621         heartbeatSchedule = context.getActorSystem().scheduler().scheduleOnce(
 622             interval, context.getActor(), new SendHeartBeat(),
 623             context.getActorSystem().dispatcher(), context.getActor());
 624     }
 625
 626     @Override
 627     public void close() throws Exception {
 628         stopHeartBeat();
 629     }
 630
 631     @Override
 632     public String getLeaderId() {
 633         return context.getId();
 634     }
 635
 636     protected boolean isLeaderIsolated() {
 637         int minPresent = minIsolatedLeaderPeerCount;
 638         for (FollowerLogInformation followerLogInformation : followerToLog.values()) {
 639             if (followerLogInformation.isFollowerActive()) {
 640                 --minPresent;
 641                 if (minPresent == 0) {
 642                     break;
 643                 }
 644             }
 645         }
 646         return (minPresent != 0);
 647     }
 648
 649     /**
 650      * Encapsulates the snapshot bytestring and handles the logic of sending
 651      * snapshot chunks
 652      */
 653     protected class FollowerToSnapshot {
 654         private final ByteString snapshotBytes;
 655         private int offset = 0;
 656         // the next snapshot chunk is sent only if the replyReceivedForOffset matches offset
 657         private int replyReceivedForOffset;
 658         // if replyStatus is false, the previous chunk is attempted
 659         private boolean replyStatus = false;
 660         private int chunkIndex;
 661         private final int totalChunks;
 662         private int lastChunkHashCode = AbstractLeader.INITIAL_LAST_CHUNK_HASH_CODE;
 663         private int nextChunkHashCode = AbstractLeader.INITIAL_LAST_CHUNK_HASH_CODE;
 664
 665         public FollowerToSnapshot(ByteString snapshotBytes) {
 666             this.snapshotBytes = snapshotBytes;
 667             int size = snapshotBytes.size();
 668             totalChunks = ( size / context.getConfigParams().getSnapshotChunkSize()) +
 669                 ((size % context.getConfigParams().getSnapshotChunkSize()) > 0 ? 1 : 0);
 670             if(LOG.isDebugEnabled()) {
 671                 LOG.debug("{}: Snapshot {} bytes, total chunks to send:{}",
 672                         context.getId(), size, totalChunks);
 673             }
 674             replyReceivedForOffset = -1;
 675             chunkIndex = AbstractLeader.FIRST_CHUNK_INDEX;
 676         }
 677
 678         public ByteString getSnapshotBytes() {
 679             return snapshotBytes;
 680         }
 681
 682         public int incrementOffset() {
 683             if(replyStatus) {
 684                 // if prev chunk failed, we would want to sent the same chunk again
 685                 offset = offset + context.getConfigParams().getSnapshotChunkSize();
 686             }
 687             return offset;
 688         }
 689
 690         public int incrementChunkIndex() {
 691             if (replyStatus) {
 692                 // if prev chunk failed, we would want to sent the same chunk again
 693                 chunkIndex =  chunkIndex + 1;
 694             }
 695             return chunkIndex;
 696         }
 697
 698         public int getChunkIndex() {
 699             return chunkIndex;
 700         }
 701
 702         public int getTotalChunks() {
 703             return totalChunks;
 704         }
 705
 706         public boolean canSendNextChunk() {
 707             // we only send a false if a chunk is sent but we have not received a reply yet
 708             return replyReceivedForOffset == offset;
 709         }
 710
 711         public boolean isLastChunk(int chunkIndex) {
 712             return totalChunks == chunkIndex;
 713         }
 714
 715         public void markSendStatus(boolean success) {
 716             if (success) {
 717                 // if the chunk sent was successful
 718                 replyReceivedForOffset = offset;
 719                 replyStatus = true;
 720                 lastChunkHashCode = nextChunkHashCode;
 721             } else {
 722                 // if the chunk sent was failure
 723                 replyReceivedForOffset = offset;
 724                 replyStatus = false;
 725             }
 726         }
 727
 728         public ByteString getNextChunk() {
 729             int snapshotLength = getSnapshotBytes().size();
 730             int start = incrementOffset();
 731             int size = context.getConfigParams().getSnapshotChunkSize();
 732             if (context.getConfigParams().getSnapshotChunkSize() > snapshotLength) {
 733                 size = snapshotLength;
 734             } else {
 735                 if ((start + context.getConfigParams().getSnapshotChunkSize()) > snapshotLength) {
 736                     size = snapshotLength - start;
 737                 }
 738             }
 739
 740             if(LOG.isDebugEnabled()) {
 741                 LOG.debug("{}: Next chunk: length={}, offset={},size={}", context.getId(),
 742                     snapshotLength, start, size);
 743             }
 744             ByteString substring = getSnapshotBytes().substring(start, start + size);
 745             nextChunkHashCode = substring.hashCode();
 746             return substring;
 747         }
 748
 749         /**
 750          * reset should be called when the Follower needs to be sent the snapshot from the beginning
 751          */
 752         public void reset(){
 753             offset = 0;
 754             replyStatus = false;
 755             replyReceivedForOffset = offset;
 756             chunkIndex = AbstractLeader.FIRST_CHUNK_INDEX;
 757             lastChunkHashCode = AbstractLeader.INITIAL_LAST_CHUNK_HASH_CODE;
 758         }
 759
 760         public int getLastChunkHashCode() {
 761             return lastChunkHashCode;
 762         }
 763     }
 764
 765     // called from example-actor for printing the follower-states
 766     public String printFollowerStates() {
 767         final StringBuilder sb = new StringBuilder();
 768
 769         sb.append('[');
 770         for (FollowerLogInformation followerLogInformation : followerToLog.values()) {
 771             sb.append('{');
 772             sb.append(followerLogInformation.getId());
 773             sb.append(" state:");
 774             sb.append(followerLogInformation.isFollowerActive());
 775             sb.append("},");
 776         }
 777         sb.append(']');
 778
 779         return sb.toString();
 780     }
 781
 782     @VisibleForTesting
 783     public FollowerLogInformation getFollower(String followerId) {
 784         return followerToLog.get(followerId);
 785     }
 786
 787     @VisibleForTesting
 788     protected void setFollowerSnapshot(String followerId, FollowerToSnapshot snapshot) {
 789         mapFollowerToSnapshot.put(followerId, snapshot);
 790     }
 791
 792     @VisibleForTesting
 793     public int followerSnapshotSize() {
 794         return mapFollowerToSnapshot.size();
 795     }
 796
 797     @VisibleForTesting
 798     public int followerLogSize() {
 799         return followerToLog.size();
 800     }
 801 }