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.Collection;
  20 import java.util.Collections;
  21 import java.util.HashMap;
  22 import java.util.Iterator;
  23 import java.util.LinkedList;
  24 import java.util.List;
  25 import java.util.Map;
  26 import java.util.Map.Entry;
  27 import javax.annotation.Nullable;
  28 import org.opendaylight.controller.cluster.raft.ClientRequestTracker;
  29 import org.opendaylight.controller.cluster.raft.ClientRequestTrackerImpl;
  30 import org.opendaylight.controller.cluster.raft.FollowerLogInformation;
  31 import org.opendaylight.controller.cluster.raft.FollowerLogInformationImpl;
  32 import org.opendaylight.controller.cluster.raft.PeerInfo;
  33 import org.opendaylight.controller.cluster.raft.RaftActorContext;
  34 import org.opendaylight.controller.cluster.raft.RaftState;
  35 import org.opendaylight.controller.cluster.raft.ReplicatedLogEntry;
  36 import org.opendaylight.controller.cluster.raft.Snapshot;
  37 import org.opendaylight.controller.cluster.raft.VotingState;
  38 import org.opendaylight.controller.cluster.raft.base.messages.Replicate;
  39 import org.opendaylight.controller.cluster.raft.base.messages.SendHeartBeat;
  40 import org.opendaylight.controller.cluster.raft.base.messages.SendInstallSnapshot;
  41 import org.opendaylight.controller.cluster.raft.messages.AppendEntries;
  42 import org.opendaylight.controller.cluster.raft.messages.AppendEntriesReply;
  43 import org.opendaylight.controller.cluster.raft.messages.InstallSnapshot;
  44 import org.opendaylight.controller.cluster.raft.messages.InstallSnapshotReply;
  45 import org.opendaylight.controller.cluster.raft.messages.RaftRPC;
  46 import org.opendaylight.controller.cluster.raft.messages.RequestVoteReply;
  47 import org.opendaylight.controller.cluster.raft.messages.UnInitializedFollowerSnapshotReply;
  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 = new HashMap<>();
  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     private int minReplicationCount;
  91
  92     private Optional<SnapshotHolder> snapshot;
  93
  94     public AbstractLeader(RaftActorContext context) {
  95         super(context, RaftState.Leader);
  96
  97         setLeaderPayloadVersion(context.getPayloadVersion());
  98
  99         for(PeerInfo peerInfo: context.getPeers()) {
 100             FollowerLogInformation followerLogInformation = new FollowerLogInformationImpl(peerInfo, -1, context);
 101             followerToLog.put(peerInfo.getId(), followerLogInformation);
 102         }
 103
 104         leaderId = context.getId();
 105
 106         LOG.debug("{}: Election: Leader has following peers: {}", logName(), getFollowerIds());
 107
 108         updateMinReplicaCount();
 109
 110         snapshot = Optional.absent();
 111
 112         // Immediately schedule a heartbeat
 113         // Upon election: send initial empty AppendEntries RPCs
 114         // (heartbeat) to each server; repeat during idle periods to
 115         // prevent election timeouts (§5.2)
 116         sendAppendEntries(0, false);
 117
 118         // It is important to schedule this heartbeat here
 119         scheduleHeartBeat(context.getConfigParams().getHeartBeatInterval());
 120     }
 121
 122     /**
 123      * Return an immutable collection of follower identifiers.
 124      *
 125      * @return Collection of follower IDs
 126      */
 127     public final Collection<String> getFollowerIds() {
 128         return followerToLog.keySet();
 129     }
 130
 131     public void addFollower(String followerId) {
 132         FollowerLogInformation followerLogInformation = new FollowerLogInformationImpl(
 133                 context.getPeerInfo(followerId), -1, context);
 134         followerToLog.put(followerId, followerLogInformation);
 135
 136         if(heartbeatSchedule == null) {
 137             scheduleHeartBeat(context.getConfigParams().getHeartBeatInterval());
 138         }
 139     }
 140
 141     public void removeFollower(String followerId) {
 142         followerToLog.remove(followerId);
 143     }
 144
 145     public void updateMinReplicaCount() {
 146         int numVoting = 0;
 147         for(PeerInfo peer: context.getPeers()) {
 148             if(peer.isVoting()) {
 149                 numVoting++;
 150             }
 151         }
 152
 153         minReplicationCount = getMajorityVoteCount(numVoting);
 154     }
 155
 156     protected int getMinIsolatedLeaderPeerCount(){
 157       //the isolated Leader peer count will be 1 less than the majority vote count.
 158         //this is because the vote count has the self vote counted in it
 159         //for e.g
 160         //0 peers = 1 votesRequired , minIsolatedLeaderPeerCount = 0
 161         //2 peers = 2 votesRequired , minIsolatedLeaderPeerCount = 1
 162         //4 peers = 3 votesRequired, minIsolatedLeaderPeerCount = 2
 163
 164         return minReplicationCount > 0 ? (minReplicationCount - 1) : 0;
 165     }
 166
 167     @VisibleForTesting
 168     void setSnapshot(@Nullable Snapshot snapshot) {
 169         if(snapshot != null) {
 170             this.snapshot = Optional.of(new SnapshotHolder(snapshot));
 171         } else {
 172             this.snapshot = Optional.absent();
 173         }
 174     }
 175
 176     @Override
 177     protected RaftActorBehavior handleAppendEntries(ActorRef sender,
 178         AppendEntries appendEntries) {
 179
 180         LOG.debug("{}: handleAppendEntries: {}", logName(), appendEntries);
 181
 182         return this;
 183     }
 184
 185     @Override
 186     protected RaftActorBehavior handleAppendEntriesReply(ActorRef sender,
 187         AppendEntriesReply appendEntriesReply) {
 188
 189         if(LOG.isTraceEnabled()) {
 190             LOG.trace("{}: handleAppendEntriesReply: {}", logName(), appendEntriesReply);
 191         }
 192
 193         // Update the FollowerLogInformation
 194         String followerId = appendEntriesReply.getFollowerId();
 195         FollowerLogInformation followerLogInformation =
 196             followerToLog.get(followerId);
 197
 198         if(followerLogInformation == null){
 199             LOG.error("{}: handleAppendEntriesReply - unknown follower {}", logName(), followerId);
 200             return this;
 201         }
 202
 203         if(followerLogInformation.timeSinceLastActivity() >
 204                 context.getConfigParams().getElectionTimeOutInterval().toMillis()) {
 205             LOG.warn("{} : handleAppendEntriesReply delayed beyond election timeout, " +
 206                             "appendEntriesReply : {}, timeSinceLastActivity : {}, lastApplied : {}, commitIndex : {}",
 207                     logName(), appendEntriesReply, followerLogInformation.timeSinceLastActivity(),
 208                     context.getLastApplied(), context.getCommitIndex());
 209         }
 210
 211         followerLogInformation.markFollowerActive();
 212         followerLogInformation.setPayloadVersion(appendEntriesReply.getPayloadVersion());
 213
 214         boolean updated = false;
 215         if (appendEntriesReply.isSuccess()) {
 216             updated = updateFollowerLogInformation(followerLogInformation, appendEntriesReply);
 217         } else {
 218             LOG.debug("{}: handleAppendEntriesReply: received unsuccessful reply: {}", logName(), appendEntriesReply);
 219
 220             long followerLastLogIndex = appendEntriesReply.getLogLastIndex();
 221             ReplicatedLogEntry followersLastLogEntry = context.getReplicatedLog().get(followerLastLogIndex);
 222             if(appendEntriesReply.isForceInstallSnapshot()) {
 223                 // Reset the followers match and next index. This is to signal that this follower has nothing
 224                 // in common with this Leader and so would require a snapshot to be installed
 225                 followerLogInformation.setMatchIndex(-1);
 226                 followerLogInformation.setNextIndex(-1);
 227
 228                 // Force initiate a snapshot capture
 229                 initiateCaptureSnapshot(followerId);
 230             } else if(followerLastLogIndex < 0 || (followersLastLogEntry != null &&
 231                     followersLastLogEntry.getTerm() == appendEntriesReply.getLogLastTerm())) {
 232                 // The follower's log is empty or the last entry is present in the leader's journal
 233                 // and the terms match so the follower is just behind the leader's journal from
 234                 // the last snapshot, if any. We'll catch up the follower quickly by starting at the
 235                 // follower's last log index.
 236
 237                 updated = updateFollowerLogInformation(followerLogInformation, appendEntriesReply);
 238             } else {
 239                 // TODO: When we find that the follower is out of sync with the
 240                 // Leader we simply decrement that followers next index by 1.
 241                 // Would it be possible to do better than this? The RAFT spec
 242                 // does not explicitly deal with it but may be something for us to
 243                 // think about.
 244
 245                 followerLogInformation.decrNextIndex();
 246             }
 247         }
 248
 249         // Now figure out if this reply warrants a change in the commitIndex
 250         // If there exists an N such that N > commitIndex, a majority
 251         // of matchIndex[i] ≥ N, and log[N].term == currentTerm:
 252         // set commitIndex = N (§5.3, §5.4).
 253         for (long N = context.getCommitIndex() + 1; ; N++) {
 254             int replicatedCount = 1;
 255
 256             for (FollowerLogInformation info : followerToLog.values()) {
 257                 if ((info.getMatchIndex() >= N) && (context.getPeerInfo(followerId).isVoting())) {
 258                     replicatedCount++;
 259                 }
 260             }
 261
 262             if (replicatedCount >= minReplicationCount) {
 263                 ReplicatedLogEntry replicatedLogEntry = context.getReplicatedLog().get(N);
 264                 if (replicatedLogEntry != null && replicatedLogEntry.getTerm() == currentTerm()) {
 265                     context.setCommitIndex(N);
 266                 } else {
 267                     break;
 268                 }
 269             } else {
 270                 break;
 271             }
 272         }
 273
 274         // Apply the change to the state machine
 275         if (context.getCommitIndex() > context.getLastApplied()) {
 276             if(LOG.isDebugEnabled()) {
 277                 LOG.debug("{}: handleAppendEntriesReply from {}: applying to log - commitIndex: {}, lastAppliedIndex: {}",
 278                         logName(), followerId, context.getCommitIndex(), context.getLastApplied());
 279             }
 280
 281             applyLogToStateMachine(context.getCommitIndex());
 282         }
 283
 284         if (!context.getSnapshotManager().isCapturing()) {
 285             purgeInMemoryLog();
 286         }
 287
 288         //Send the next log entry immediately, if possible, no need to wait for heartbeat to trigger that event
 289         sendUpdatesToFollower(followerId, followerLogInformation, false, !updated);
 290         return this;
 291     }
 292
 293     private boolean updateFollowerLogInformation(FollowerLogInformation followerLogInformation,
 294             AppendEntriesReply appendEntriesReply) {
 295         boolean updated = followerLogInformation.setMatchIndex(appendEntriesReply.getLogLastIndex());
 296         updated = followerLogInformation.setNextIndex(appendEntriesReply.getLogLastIndex() + 1) || updated;
 297
 298         if(updated && LOG.isDebugEnabled()) {
 299             LOG.debug("{}: handleAppendEntriesReply - FollowerLogInformation for {} updated: matchIndex: {}, nextIndex: {}",
 300                     logName(), followerLogInformation.getId(), followerLogInformation.getMatchIndex(),
 301                     followerLogInformation.getNextIndex());
 302         }
 303         return updated;
 304     }
 305
 306     private void purgeInMemoryLog() {
 307         //find the lowest index across followers which has been replicated to all.
 308         // lastApplied if there are no followers, so that we keep clearing the log for single-node
 309         // we would delete the in-mem log from that index on, in-order to minimize mem usage
 310         // we would also share this info thru AE with the followers so that they can delete their log entries as well.
 311         long minReplicatedToAllIndex = followerToLog.isEmpty() ? context.getLastApplied() : Long.MAX_VALUE;
 312         for (FollowerLogInformation info : followerToLog.values()) {
 313             minReplicatedToAllIndex = Math.min(minReplicatedToAllIndex, info.getMatchIndex());
 314         }
 315
 316         super.performSnapshotWithoutCapture(minReplicatedToAllIndex);
 317     }
 318
 319     @Override
 320     protected ClientRequestTracker removeClientRequestTracker(long logIndex) {
 321         final Iterator<ClientRequestTracker> it = trackerList.iterator();
 322         while (it.hasNext()) {
 323             final ClientRequestTracker t = it.next();
 324             if (t.getIndex() == logIndex) {
 325                 it.remove();
 326                 return t;
 327             }
 328         }
 329
 330         return null;
 331     }
 332
 333     @Override
 334     protected ClientRequestTracker findClientRequestTracker(long logIndex) {
 335         for (ClientRequestTracker tracker : trackerList) {
 336             if (tracker.getIndex() == logIndex) {
 337                 return tracker;
 338             }
 339         }
 340         return null;
 341     }
 342
 343     @Override
 344     protected RaftActorBehavior handleRequestVoteReply(ActorRef sender,
 345         RequestVoteReply requestVoteReply) {
 346         return this;
 347     }
 348
 349     protected void beforeSendHeartbeat(){}
 350
 351     @Override
 352     public RaftActorBehavior handleMessage(ActorRef sender, Object originalMessage) {
 353         Preconditions.checkNotNull(sender, "sender should not be null");
 354
 355         Object message = fromSerializableMessage(originalMessage);
 356
 357         if (message instanceof RaftRPC) {
 358             RaftRPC rpc = (RaftRPC) message;
 359             // If RPC request or response contains term T > currentTerm:
 360             // set currentTerm = T, convert to follower (§5.1)
 361             // This applies to all RPC messages and responses
 362             if (rpc.getTerm() > context.getTermInformation().getCurrentTerm()) {
 363                 LOG.debug("{}: Term {} in \"{}\" message is greater than leader's term {} - switching to Follower",
 364                         logName(), rpc.getTerm(), rpc, context.getTermInformation().getCurrentTerm());
 365
 366                 context.getTermInformation().updateAndPersist(rpc.getTerm(), null);
 367
 368                 return internalSwitchBehavior(RaftState.Follower);
 369             }
 370         }
 371
 372         if (message instanceof SendHeartBeat) {
 373             beforeSendHeartbeat();
 374             sendHeartBeat();
 375             scheduleHeartBeat(context.getConfigParams().getHeartBeatInterval());
 376             return this;
 377
 378         } else if(message instanceof SendInstallSnapshot) {
 379             // received from RaftActor
 380             setSnapshot(((SendInstallSnapshot) message).getSnapshot());
 381             sendInstallSnapshot();
 382
 383         } else if (message instanceof Replicate) {
 384             replicate((Replicate) message);
 385
 386         } else if (message instanceof InstallSnapshotReply){
 387             handleInstallSnapshotReply((InstallSnapshotReply) message);
 388
 389         }
 390
 391
 392         return super.handleMessage(sender, message);
 393     }
 394
 395     private void handleInstallSnapshotReply(InstallSnapshotReply reply) {
 396         LOG.debug("{}: handleInstallSnapshotReply: {}", logName(), reply);
 397
 398         String followerId = reply.getFollowerId();
 399         FollowerToSnapshot followerToSnapshot = mapFollowerToSnapshot.get(followerId);
 400
 401         if (followerToSnapshot == null) {
 402             LOG.error("{}: FollowerToSnapshot not found for follower {} in InstallSnapshotReply",
 403                     logName(), followerId);
 404             return;
 405         }
 406
 407         FollowerLogInformation followerLogInformation = followerToLog.get(followerId);
 408         if(followerLogInformation == null) {
 409             // This can happen during AddServer if it times out.
 410             LOG.error("{}: FollowerLogInformation not found for follower {} in InstallSnapshotReply",
 411                     logName(), followerId);
 412             mapFollowerToSnapshot.remove(followerId);
 413             return;
 414         }
 415
 416         followerLogInformation.markFollowerActive();
 417
 418         if (followerToSnapshot.getChunkIndex() == reply.getChunkIndex()) {
 419             boolean wasLastChunk = false;
 420             if (reply.isSuccess()) {
 421                 if(followerToSnapshot.isLastChunk(reply.getChunkIndex())) {
 422                     //this was the last chunk reply
 423                     if(LOG.isDebugEnabled()) {
 424                         LOG.debug("{}: InstallSnapshotReply received, " +
 425                                 "last chunk received, Chunk: {}. Follower: {} Setting nextIndex: {}",
 426                                 logName(), reply.getChunkIndex(), followerId,
 427                             context.getReplicatedLog().getSnapshotIndex() + 1
 428                         );
 429                     }
 430
 431                     long followerMatchIndex = snapshot.get().getLastIncludedIndex();
 432                     followerLogInformation.setMatchIndex(followerMatchIndex);
 433                     followerLogInformation.setNextIndex(followerMatchIndex + 1);
 434                     mapFollowerToSnapshot.remove(followerId);
 435
 436                     LOG.debug("{}: follower: {}, matchIndex set to {}, nextIndex set to {}",
 437                         logName(), followerId, followerLogInformation.getMatchIndex(),
 438                         followerLogInformation.getNextIndex());
 439
 440                     if (mapFollowerToSnapshot.isEmpty()) {
 441                         // once there are no pending followers receiving snapshots
 442                         // we can remove snapshot from the memory
 443                         setSnapshot(null);
 444                     }
 445                     wasLastChunk = true;
 446                     if(context.getPeerInfo(followerId).getVotingState() == VotingState.VOTING_NOT_INITIALIZED){
 447                         UnInitializedFollowerSnapshotReply unInitFollowerSnapshotSuccess =
 448                                              new UnInitializedFollowerSnapshotReply(followerId);
 449                         context.getActor().tell(unInitFollowerSnapshotSuccess, context.getActor());
 450                         LOG.debug("Sent message UnInitializedFollowerSnapshotReply to self");
 451                     }
 452                 } else {
 453                     followerToSnapshot.markSendStatus(true);
 454                 }
 455             } else {
 456                 LOG.info("{}: InstallSnapshotReply received sending snapshot chunk failed, Will retry, Chunk: {}",
 457                         logName(), reply.getChunkIndex());
 458
 459                 followerToSnapshot.markSendStatus(false);
 460             }
 461
 462             if (wasLastChunk && !context.getSnapshotManager().isCapturing()) {
 463                 // Since the follower is now caught up try to purge the log.
 464                 purgeInMemoryLog();
 465             } else if (!wasLastChunk && followerToSnapshot.canSendNextChunk()) {
 466                 ActorSelection followerActor = context.getPeerActorSelection(followerId);
 467                 if(followerActor != null) {
 468                     sendSnapshotChunk(followerActor, followerId);
 469                 }
 470             }
 471
 472         } else {
 473             LOG.error("{}: Chunk index {} in InstallSnapshotReply from follower {} does not match expected index {}",
 474                     logName(), reply.getChunkIndex(), followerId,
 475                     followerToSnapshot.getChunkIndex());
 476
 477             if(reply.getChunkIndex() == INVALID_CHUNK_INDEX){
 478                 // Since the Follower did not find this index to be valid we should reset the follower snapshot
 479                 // so that Installing the snapshot can resume from the beginning
 480                 followerToSnapshot.reset();
 481             }
 482         }
 483     }
 484
 485     private void replicate(Replicate replicate) {
 486         long logIndex = replicate.getReplicatedLogEntry().getIndex();
 487
 488         LOG.debug("{}: Replicate message: identifier: {}, logIndex: {}", logName(),
 489                 replicate.getIdentifier(), logIndex);
 490
 491         // Create a tracker entry we will use this later to notify the
 492         // client actor
 493         trackerList.add(
 494             new ClientRequestTrackerImpl(replicate.getClientActor(),
 495                 replicate.getIdentifier(),
 496                 logIndex)
 497         );
 498
 499         boolean applyModificationToState = followerToLog.isEmpty()
 500                 || context.getRaftPolicy().applyModificationToStateBeforeConsensus();
 501
 502         if(applyModificationToState){
 503             context.setCommitIndex(logIndex);
 504             applyLogToStateMachine(logIndex);
 505         }
 506
 507         if (!followerToLog.isEmpty()) {
 508             sendAppendEntries(0, false);
 509         }
 510     }
 511
 512     protected void sendAppendEntries(long timeSinceLastActivityInterval, boolean isHeartbeat) {
 513         // Send an AppendEntries to all followers
 514         for (Entry<String, FollowerLogInformation> e : followerToLog.entrySet()) {
 515             final String followerId = e.getKey();
 516             final FollowerLogInformation followerLogInformation = e.getValue();
 517             // This checks helps not to send a repeat message to the follower
 518             if(!followerLogInformation.isFollowerActive() ||
 519                     followerLogInformation.timeSinceLastActivity() >= timeSinceLastActivityInterval) {
 520                 sendUpdatesToFollower(followerId, followerLogInformation, true, isHeartbeat);
 521             }
 522         }
 523     }
 524
 525     /**
 526      *
 527      * This method checks if any update needs to be sent to the given follower. This includes append log entries,
 528      * sending next snapshot chunk, and initiating a snapshot.
 529      * @return true if any update is sent, false otherwise
 530      */
 531
 532     private void sendUpdatesToFollower(String followerId, FollowerLogInformation followerLogInformation,
 533                                        boolean sendHeartbeat, boolean isHeartbeat) {
 534
 535         ActorSelection followerActor = context.getPeerActorSelection(followerId);
 536         if (followerActor != null) {
 537             long followerNextIndex = followerLogInformation.getNextIndex();
 538             boolean isFollowerActive = followerLogInformation.isFollowerActive();
 539             boolean sendAppendEntries = false;
 540             List<ReplicatedLogEntry> entries = Collections.emptyList();
 541
 542             if (mapFollowerToSnapshot.get(followerId) != null) {
 543                 // if install snapshot is in process , then sent next chunk if possible
 544                 if (isFollowerActive && mapFollowerToSnapshot.get(followerId).canSendNextChunk()) {
 545                     sendSnapshotChunk(followerActor, followerId);
 546                 } else if(sendHeartbeat) {
 547                     // we send a heartbeat even if we have not received a reply for the last chunk
 548                     sendAppendEntries = true;
 549                 }
 550             } else {
 551                 long leaderLastIndex = context.getReplicatedLog().lastIndex();
 552                 long leaderSnapShotIndex = context.getReplicatedLog().getSnapshotIndex();
 553
 554                 if((!isHeartbeat && LOG.isDebugEnabled()) || LOG.isTraceEnabled()) {
 555                     LOG.debug("{}: Checking sendAppendEntries for follower {}: active: {}, followerNextIndex: {}, leaderLastIndex: {}, leaderSnapShotIndex: {}",
 556                             logName(), followerId, isFollowerActive, followerNextIndex, leaderLastIndex, leaderSnapShotIndex);
 557                 }
 558
 559                 if (isFollowerActive && context.getReplicatedLog().isPresent(followerNextIndex)) {
 560
 561                     LOG.debug("{}: sendAppendEntries: {} is present for follower {}", logName(),
 562                             followerNextIndex, followerId);
 563
 564                     if(followerLogInformation.okToReplicate()) {
 565                         // Try to send all the entries in the journal but not exceeding the max data size
 566                         // for a single AppendEntries message.
 567                         int maxEntries = (int) context.getReplicatedLog().size();
 568                         entries = context.getReplicatedLog().getFrom(followerNextIndex, maxEntries,
 569                                 context.getConfigParams().getSnapshotChunkSize());
 570                         sendAppendEntries = true;
 571                     }
 572                 } else if (isFollowerActive && followerNextIndex >= 0 &&
 573                     leaderLastIndex > followerNextIndex && !context.getSnapshotManager().isCapturing()) {
 574                     // if the followers next index is not present in the leaders log, and
 575                     // if the follower is just not starting and if leader's index is more than followers index
 576                     // then snapshot should be sent
 577
 578                     if (LOG.isDebugEnabled()) {
 579                         LOG.debug(String.format("%s: InitiateInstallSnapshot to follower: %s," +
 580                                     "follower-nextIndex: %d, leader-snapshot-index: %d,  " +
 581                                     "leader-last-index: %d", logName(), followerId,
 582                                     followerNextIndex, leaderSnapShotIndex, leaderLastIndex));
 583                     }
 584
 585                     // Send heartbeat to follower whenever install snapshot is initiated.
 586                     sendAppendEntries = true;
 587                     if (canInstallSnapshot(followerNextIndex)) {
 588                         initiateCaptureSnapshot(followerId);
 589                     }
 590
 591                 } else if(sendHeartbeat) {
 592                     // we send an AppendEntries, even if the follower is inactive
 593                     // in-order to update the followers timestamp, in case it becomes active again
 594                     sendAppendEntries = true;
 595                 }
 596
 597             }
 598
 599             if(sendAppendEntries) {
 600                 sendAppendEntriesToFollower(followerActor, followerNextIndex,
 601                         entries, followerId);
 602             }
 603         }
 604     }
 605
 606     private void sendAppendEntriesToFollower(ActorSelection followerActor, long followerNextIndex,
 607         List<ReplicatedLogEntry> entries, String followerId) {
 608         AppendEntries appendEntries = new AppendEntries(currentTerm(), context.getId(),
 609             prevLogIndex(followerNextIndex),
 610             prevLogTerm(followerNextIndex), entries,
 611             context.getCommitIndex(), super.getReplicatedToAllIndex(), context.getPayloadVersion());
 612
 613         if(!entries.isEmpty() || LOG.isTraceEnabled()) {
 614             LOG.debug("{}: Sending AppendEntries to follower {}: {}", logName(), followerId,
 615                     appendEntries);
 616         }
 617
 618         followerActor.tell(appendEntries.toSerializable(), actor());
 619     }
 620
 621     /**
 622      * Install Snapshot works as follows
 623      * 1. Leader initiates the capture snapshot by sending a CaptureSnapshot message to actor
 624      * 2. RaftActor on receipt of the CaptureSnapshotReply (from Shard), stores the received snapshot in the replicated log
 625      * and makes a call to Leader's handleMessage , with SendInstallSnapshot message.
 626      * 3. Leader , picks the snapshot from im-mem ReplicatedLog and sends it in chunks to the Follower
 627      * 4. On complete, Follower sends back a InstallSnapshotReply.
 628      * 5. On receipt of the InstallSnapshotReply for the last chunk, Leader marks the install complete for that follower
 629      * and replenishes the memory by deleting the snapshot in Replicated log.
 630      * 6. If another follower requires a snapshot and a snapshot has been collected (via CaptureSnapshotReply)
 631      * then send the existing snapshot in chunks to the follower.
 632      * @param followerId
 633      */
 634     public boolean initiateCaptureSnapshot(String followerId) {
 635         if (snapshot.isPresent()) {
 636             // if a snapshot is present in the memory, most likely another install is in progress
 637             // no need to capture snapshot.
 638             // This could happen if another follower needs an install when one is going on.
 639             final ActorSelection followerActor = context.getPeerActorSelection(followerId);
 640             sendSnapshotChunk(followerActor, followerId);
 641             return true;
 642         } else {
 643             return context.getSnapshotManager().captureToInstall(context.getReplicatedLog().last(),
 644                     this.getReplicatedToAllIndex(), followerId);
 645         }
 646     }
 647
 648     private boolean canInstallSnapshot(long nextIndex){
 649         // If the follower's nextIndex is -1 then we might as well send it a snapshot
 650         // Otherwise send it a snapshot only if the nextIndex is not present in the log but is present
 651         // in the snapshot
 652         return (nextIndex == -1 ||
 653                 (!context.getReplicatedLog().isPresent(nextIndex)
 654                         && context.getReplicatedLog().isInSnapshot(nextIndex)));
 655
 656     }
 657
 658
 659     private void sendInstallSnapshot() {
 660         LOG.debug("{}: sendInstallSnapshot", logName());
 661         for (Entry<String, FollowerLogInformation> e : followerToLog.entrySet()) {
 662             String followerId = e.getKey();
 663             ActorSelection followerActor = context.getPeerActorSelection(followerId);
 664             FollowerLogInformation followerLogInfo = e.getValue();
 665
 666             if (followerActor != null) {
 667                 long nextIndex = followerLogInfo.getNextIndex();
 668                 if (context.getPeerInfo(followerId).getVotingState() == VotingState.VOTING_NOT_INITIALIZED ||
 669                         canInstallSnapshot(nextIndex)) {
 670                     sendSnapshotChunk(followerActor, followerId);
 671                 }
 672             }
 673         }
 674     }
 675
 676     /**
 677      *  Sends a snapshot chunk to a given follower
 678      *  InstallSnapshot should qualify as a heartbeat too.
 679      */
 680     private void sendSnapshotChunk(ActorSelection followerActor, String followerId) {
 681         try {
 682             if (snapshot.isPresent()) {
 683                 ByteString nextSnapshotChunk = getNextSnapshotChunk(followerId, snapshot.get().getSnapshotBytes());
 684
 685                 // Note: the previous call to getNextSnapshotChunk has the side-effect of adding
 686                 // followerId to the followerToSnapshot map.
 687                 FollowerToSnapshot followerToSnapshot = mapFollowerToSnapshot.get(followerId);
 688
 689                 followerActor.tell(
 690                     new InstallSnapshot(currentTerm(), context.getId(),
 691                         snapshot.get().getLastIncludedIndex(),
 692                         snapshot.get().getLastIncludedTerm(),
 693                         nextSnapshotChunk,
 694                         followerToSnapshot.incrementChunkIndex(),
 695                         followerToSnapshot.getTotalChunks(),
 696                         Optional.of(followerToSnapshot.getLastChunkHashCode())
 697                     ).toSerializable(),
 698                     actor()
 699                 );
 700
 701                 if(LOG.isDebugEnabled()) {
 702                     LOG.debug("{}: InstallSnapshot sent to follower {}, Chunk: {}/{}",
 703                             logName(), followerActor.path(), followerToSnapshot.getChunkIndex(),
 704                             followerToSnapshot.getTotalChunks());
 705                 }
 706             }
 707         } catch (IOException e) {
 708             LOG.error("{}: InstallSnapshot failed for Leader.", logName(), e);
 709         }
 710     }
 711
 712     /**
 713      * Acccepts snaphot as ByteString, enters into map for future chunks
 714      * creates and return a ByteString chunk
 715      */
 716     private ByteString getNextSnapshotChunk(String followerId, ByteString snapshotBytes) throws IOException {
 717         FollowerToSnapshot followerToSnapshot = mapFollowerToSnapshot.get(followerId);
 718         if (followerToSnapshot == null) {
 719             followerToSnapshot = new FollowerToSnapshot(snapshotBytes);
 720             mapFollowerToSnapshot.put(followerId, followerToSnapshot);
 721         }
 722         ByteString nextChunk = followerToSnapshot.getNextChunk();
 723
 724         LOG.debug("{}: next snapshot chunk size for follower {}: {}", logName(), followerId, nextChunk.size());
 725
 726         return nextChunk;
 727     }
 728
 729     private void sendHeartBeat() {
 730         if (!followerToLog.isEmpty()) {
 731             LOG.trace("{}: Sending heartbeat", logName());
 732             sendAppendEntries(context.getConfigParams().getHeartBeatInterval().toMillis(), true);
 733         }
 734     }
 735
 736     private void stopHeartBeat() {
 737         if (heartbeatSchedule != null && !heartbeatSchedule.isCancelled()) {
 738             heartbeatSchedule.cancel();
 739         }
 740     }
 741
 742     private void scheduleHeartBeat(FiniteDuration interval) {
 743         if (followerToLog.isEmpty()) {
 744             // Optimization - do not bother scheduling a heartbeat as there are
 745             // no followers
 746             return;
 747         }
 748
 749         stopHeartBeat();
 750
 751         // Schedule a heartbeat. When the scheduler triggers a SendHeartbeat
 752         // message is sent to itself.
 753         // Scheduling the heartbeat only once here because heartbeats do not
 754         // need to be sent if there are other messages being sent to the remote
 755         // actor.
 756         heartbeatSchedule = context.getActorSystem().scheduler().scheduleOnce(
 757             interval, context.getActor(), new SendHeartBeat(),
 758             context.getActorSystem().dispatcher(), context.getActor());
 759     }
 760
 761     @Override
 762     public void close() throws Exception {
 763         stopHeartBeat();
 764     }
 765
 766     @Override
 767     public String getLeaderId() {
 768         return context.getId();
 769     }
 770
 771     protected boolean isLeaderIsolated() {
 772         int minPresent = getMinIsolatedLeaderPeerCount();
 773         for (FollowerLogInformation followerLogInformation : followerToLog.values()) {
 774             if (followerLogInformation.isFollowerActive()) {
 775                 --minPresent;
 776                 if (minPresent == 0) {
 777                     break;
 778                 }
 779             }
 780         }
 781         return (minPresent != 0);
 782     }
 783
 784     /**
 785      * Encapsulates the snapshot bytestring and handles the logic of sending
 786      * snapshot chunks
 787      */
 788     protected class FollowerToSnapshot {
 789         private final ByteString snapshotBytes;
 790         private int offset = 0;
 791         // the next snapshot chunk is sent only if the replyReceivedForOffset matches offset
 792         private int replyReceivedForOffset;
 793         // if replyStatus is false, the previous chunk is attempted
 794         private boolean replyStatus = false;
 795         private int chunkIndex;
 796         private final int totalChunks;
 797         private int lastChunkHashCode = AbstractLeader.INITIAL_LAST_CHUNK_HASH_CODE;
 798         private int nextChunkHashCode = AbstractLeader.INITIAL_LAST_CHUNK_HASH_CODE;
 799
 800         public FollowerToSnapshot(ByteString snapshotBytes) {
 801             this.snapshotBytes = snapshotBytes;
 802             int size = snapshotBytes.size();
 803             totalChunks = ( size / context.getConfigParams().getSnapshotChunkSize()) +
 804                 ((size % context.getConfigParams().getSnapshotChunkSize()) > 0 ? 1 : 0);
 805             if(LOG.isDebugEnabled()) {
 806                 LOG.debug("{}: Snapshot {} bytes, total chunks to send:{}",
 807                         logName(), size, totalChunks);
 808             }
 809             replyReceivedForOffset = -1;
 810             chunkIndex = AbstractLeader.FIRST_CHUNK_INDEX;
 811         }
 812
 813         public ByteString getSnapshotBytes() {
 814             return snapshotBytes;
 815         }
 816
 817         public int incrementOffset() {
 818             if(replyStatus) {
 819                 // if prev chunk failed, we would want to sent the same chunk again
 820                 offset = offset + context.getConfigParams().getSnapshotChunkSize();
 821             }
 822             return offset;
 823         }
 824
 825         public int incrementChunkIndex() {
 826             if (replyStatus) {
 827                 // if prev chunk failed, we would want to sent the same chunk again
 828                 chunkIndex =  chunkIndex + 1;
 829             }
 830             return chunkIndex;
 831         }
 832
 833         public int getChunkIndex() {
 834             return chunkIndex;
 835         }
 836
 837         public int getTotalChunks() {
 838             return totalChunks;
 839         }
 840
 841         public boolean canSendNextChunk() {
 842             // we only send a false if a chunk is sent but we have not received a reply yet
 843             return replyReceivedForOffset == offset;
 844         }
 845
 846         public boolean isLastChunk(int chunkIndex) {
 847             return totalChunks == chunkIndex;
 848         }
 849
 850         public void markSendStatus(boolean success) {
 851             if (success) {
 852                 // if the chunk sent was successful
 853                 replyReceivedForOffset = offset;
 854                 replyStatus = true;
 855                 lastChunkHashCode = nextChunkHashCode;
 856             } else {
 857                 // if the chunk sent was failure
 858                 replyReceivedForOffset = offset;
 859                 replyStatus = false;
 860             }
 861         }
 862
 863         public ByteString getNextChunk() {
 864             int snapshotLength = getSnapshotBytes().size();
 865             int start = incrementOffset();
 866             int size = context.getConfigParams().getSnapshotChunkSize();
 867             if (context.getConfigParams().getSnapshotChunkSize() > snapshotLength) {
 868                 size = snapshotLength;
 869             } else {
 870                 if ((start + context.getConfigParams().getSnapshotChunkSize()) > snapshotLength) {
 871                     size = snapshotLength - start;
 872                 }
 873             }
 874
 875
 876             LOG.debug("{}: Next chunk: length={}, offset={},size={}", logName(),
 877                     snapshotLength, start, size);
 878
 879             ByteString substring = getSnapshotBytes().substring(start, start + size);
 880             nextChunkHashCode = substring.hashCode();
 881             return substring;
 882         }
 883
 884         /**
 885          * reset should be called when the Follower needs to be sent the snapshot from the beginning
 886          */
 887         public void reset(){
 888             offset = 0;
 889             replyStatus = false;
 890             replyReceivedForOffset = offset;
 891             chunkIndex = AbstractLeader.FIRST_CHUNK_INDEX;
 892             lastChunkHashCode = AbstractLeader.INITIAL_LAST_CHUNK_HASH_CODE;
 893         }
 894
 895         public int getLastChunkHashCode() {
 896             return lastChunkHashCode;
 897         }
 898     }
 899
 900     // called from example-actor for printing the follower-states
 901     public String printFollowerStates() {
 902         final StringBuilder sb = new StringBuilder();
 903
 904         sb.append('[');
 905         for (FollowerLogInformation followerLogInformation : followerToLog.values()) {
 906             sb.append('{');
 907             sb.append(followerLogInformation.getId());
 908             sb.append(" state:");
 909             sb.append(followerLogInformation.isFollowerActive());
 910             sb.append("},");
 911         }
 912         sb.append(']');
 913
 914         return sb.toString();
 915     }
 916
 917     @VisibleForTesting
 918     public FollowerLogInformation getFollower(String followerId) {
 919         return followerToLog.get(followerId);
 920     }
 921
 922     @VisibleForTesting
 923     protected void setFollowerSnapshot(String followerId, FollowerToSnapshot snapshot) {
 924         mapFollowerToSnapshot.put(followerId, snapshot);
 925     }
 926
 927     @VisibleForTesting
 928     public int followerSnapshotSize() {
 929         return mapFollowerToSnapshot.size();
 930     }
 931
 932     @VisibleForTesting
 933     public int followerLogSize() {
 934         return followerToLog.size();
 935     }
 936
 937     private static class SnapshotHolder {
 938         private final long lastIncludedTerm;
 939         private final long lastIncludedIndex;
 940         private final ByteString snapshotBytes;
 941
 942         SnapshotHolder(Snapshot snapshot) {
 943             this.lastIncludedTerm = snapshot.getLastAppliedTerm();
 944             this.lastIncludedIndex = snapshot.getLastAppliedIndex();
 945             this.snapshotBytes = ByteString.copyFrom(snapshot.getState());
 946         }
 947
 948         long getLastIncludedTerm() {
 949             return lastIncludedTerm;
 950         }
 951
 952         long getLastIncludedIndex() {
 953             return lastIncludedIndex;
 954         }
 955
 956         ByteString getSnapshotBytes() {
 957             return snapshotBytes;
 958         }
 959     }
 960 }