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.FollowerLogInformation.FollowerState;
  32 import org.opendaylight.controller.cluster.raft.FollowerLogInformationImpl;
  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.base.messages.Replicate;
  38 import org.opendaylight.controller.cluster.raft.base.messages.SendHeartBeat;
  39 import org.opendaylight.controller.cluster.raft.base.messages.SendInstallSnapshot;
  40 import org.opendaylight.controller.cluster.raft.messages.AppendEntries;
  41 import org.opendaylight.controller.cluster.raft.messages.AppendEntriesReply;
  42 import org.opendaylight.controller.cluster.raft.messages.InstallSnapshot;
  43 import org.opendaylight.controller.cluster.raft.messages.InstallSnapshotReply;
  44 import org.opendaylight.controller.cluster.raft.messages.RaftRPC;
  45 import org.opendaylight.controller.cluster.raft.messages.RequestVoteReply;
  46 import org.opendaylight.controller.cluster.raft.messages.UnInitializedFollowerSnapshotReply;
  47 import scala.concurrent.duration.FiniteDuration;
  48
  49 /**
  50  * The behavior of a RaftActor when it is in the Leader state
  51  * <p/>
  52  * Leaders:
  53  * <ul>
  54  * <li> Upon election: send initial empty AppendEntries RPCs
  55  * (heartbeat) to each server; repeat during idle periods to
  56  * prevent election timeouts (§5.2)
  57  * <li> If command received from client: append entry to local log,
  58  * respond after entry applied to state machine (§5.3)
  59  * <li> If last log index ≥ nextIndex for a follower: send
  60  * AppendEntries RPC with log entries starting at nextIndex
  61  * <ul>
  62  * <li> If successful: update nextIndex and matchIndex for
  63  * follower (§5.3)
  64  * <li> If AppendEntries fails because of log inconsistency:
  65  * decrement nextIndex and retry (§5.3)
  66  * </ul>
  67  * <li> If there exists an N such that N > commitIndex, a majority
  68  * of matchIndex[i] ≥ N, and log[N].term == currentTerm:
  69  * set commitIndex = N (§5.3, §5.4).
  70  */
  71 public abstract class AbstractLeader extends AbstractRaftActorBehavior {
  72
  73     // The index of the first chunk that is sent when installing a snapshot
  74     public static final int FIRST_CHUNK_INDEX = 1;
  75
  76     // The index that the follower should respond with if it needs the install snapshot to be reset
  77     public static final int INVALID_CHUNK_INDEX = -1;
  78
  79     // This would be passed as the hash code of the last chunk when sending the first chunk
  80     public static final int INITIAL_LAST_CHUNK_HASH_CODE = -1;
  81
  82     private final Map<String, FollowerLogInformation> followerToLog = new HashMap<>();
  83     private final Map<String, FollowerToSnapshot> mapFollowerToSnapshot = new HashMap<>();
  84
  85     private Cancellable heartbeatSchedule = null;
  86
  87     private final Collection<ClientRequestTracker> trackerList = new LinkedList<>();
  88
  89     private int minReplicationCount;
  90
  91     private int minIsolatedLeaderPeerCount;
  92
  93     private Optional<SnapshotHolder> snapshot;
  94
  95     public AbstractLeader(RaftActorContext context) {
  96         super(context, RaftState.Leader);
  97
  98         setLeaderPayloadVersion(context.getPayloadVersion());
  99
 100         for (String followerId : context.getPeerAddresses().keySet()) {
 101             FollowerLogInformation followerLogInformation =
 102                 new FollowerLogInformationImpl(followerId, -1, context);
 103
 104             followerToLog.put(followerId, followerLogInformation);
 105         }
 106
 107         leaderId = context.getId();
 108
 109         LOG.debug("{}: Election: Leader has following peers: {}", logName(), getFollowerIds());
 110
 111         updateMinReplicaCountAndMinIsolatedLeaderPeerCount();
 112
 113         snapshot = Optional.absent();
 114
 115         // Immediately schedule a heartbeat
 116         // Upon election: send initial empty AppendEntries RPCs
 117         // (heartbeat) to each server; repeat during idle periods to
 118         // prevent election timeouts (§5.2)
 119         sendAppendEntries(0, false);
 120
 121         // It is important to schedule this heartbeat here
 122         scheduleHeartBeat(context.getConfigParams().getHeartBeatInterval());
 123     }
 124
 125     /**
 126      * Return an immutable collection of follower identifiers.
 127      *
 128      * @return Collection of follower IDs
 129      */
 130     public final Collection<String> getFollowerIds() {
 131         return followerToLog.keySet();
 132     }
 133
 134     public void addFollower(String followerId, FollowerState followerState) {
 135         FollowerLogInformation followerLogInformation = new FollowerLogInformationImpl(followerId, -1, context);
 136         followerLogInformation.setFollowerState(followerState);
 137         followerToLog.put(followerId, followerLogInformation);
 138     }
 139
 140     public void removeFollower(String followerId) {
 141         followerToLog.remove(followerId);
 142     }
 143
 144     public void updateMinReplicaCountAndMinIsolatedLeaderPeerCount(){
 145         minReplicationCount = getMajorityVoteCount(getFollowerIds().size());
 146
 147         //the isolated Leader peer count will be 1 less than the majority vote count.
 148         //this is because the vote count has the self vote counted in it
 149         //for e.g
 150         //0 peers = 1 votesRequired , minIsolatedLeaderPeerCount = 0
 151         //2 peers = 2 votesRequired , minIsolatedLeaderPeerCount = 1
 152         //4 peers = 3 votesRequired, minIsolatedLeaderPeerCount = 2
 153         minIsolatedLeaderPeerCount = minReplicationCount > 0 ? (minReplicationCount - 1) : 0;
 154     }
 155
 156     public int getMinIsolatedLeaderPeerCount(){
 157         return minIsolatedLeaderPeerCount;
 158     }
 159
 160     @VisibleForTesting
 161     void setSnapshot(@Nullable Snapshot snapshot) {
 162         if(snapshot != null) {
 163             this.snapshot = Optional.of(new SnapshotHolder(snapshot));
 164         } else {
 165             this.snapshot = Optional.absent();
 166         }
 167     }
 168
 169     @Override
 170     protected RaftActorBehavior handleAppendEntries(ActorRef sender,
 171         AppendEntries appendEntries) {
 172
 173         LOG.debug("{}: handleAppendEntries: {}", logName(), appendEntries);
 174
 175         return this;
 176     }
 177
 178     @Override
 179     protected RaftActorBehavior handleAppendEntriesReply(ActorRef sender,
 180         AppendEntriesReply appendEntriesReply) {
 181
 182         if(LOG.isTraceEnabled()) {
 183             LOG.trace("{}: handleAppendEntriesReply: {}", logName(), appendEntriesReply);
 184         }
 185
 186         // Update the FollowerLogInformation
 187         String followerId = appendEntriesReply.getFollowerId();
 188         FollowerLogInformation followerLogInformation =
 189             followerToLog.get(followerId);
 190
 191         if(followerLogInformation == null){
 192             LOG.error("{}: handleAppendEntriesReply - unknown follower {}", logName(), followerId);
 193             return this;
 194         }
 195
 196         if(followerLogInformation.timeSinceLastActivity() >
 197                 context.getConfigParams().getElectionTimeOutInterval().toMillis()) {
 198             LOG.warn("{} : handleAppendEntriesReply delayed beyond election timeout, " +
 199                             "appendEntriesReply : {}, timeSinceLastActivity : {}, lastApplied : {}, commitIndex : {}",
 200                     logName(), appendEntriesReply, followerLogInformation.timeSinceLastActivity(),
 201                     context.getLastApplied(), context.getCommitIndex());
 202         }
 203
 204         followerLogInformation.markFollowerActive();
 205         followerLogInformation.setPayloadVersion(appendEntriesReply.getPayloadVersion());
 206
 207         boolean updated = false;
 208         if (appendEntriesReply.isSuccess()) {
 209             updated = updateFollowerLogInformation(followerLogInformation, appendEntriesReply);
 210         } else {
 211             LOG.debug("{}: handleAppendEntriesReply: received unsuccessful reply: {}", logName(), appendEntriesReply);
 212
 213             long followerLastLogIndex = appendEntriesReply.getLogLastIndex();
 214             ReplicatedLogEntry followersLastLogEntry = context.getReplicatedLog().get(followerLastLogIndex);
 215             if(appendEntriesReply.isForceInstallSnapshot()) {
 216                 // Reset the followers match and next index. This is to signal that this follower has nothing
 217                 // in common with this Leader and so would require a snapshot to be installed
 218                 followerLogInformation.setMatchIndex(-1);
 219                 followerLogInformation.setNextIndex(-1);
 220
 221                 // Force initiate a snapshot capture
 222                 initiateCaptureSnapshot(followerId);
 223             } else if(followerLastLogIndex < 0 || (followersLastLogEntry != null &&
 224                     followersLastLogEntry.getTerm() == appendEntriesReply.getLogLastTerm())) {
 225                 // The follower's log is empty or the last entry is present in the leader's journal
 226                 // and the terms match so the follower is just behind the leader's journal from
 227                 // the last snapshot, if any. We'll catch up the follower quickly by starting at the
 228                 // follower's last log index.
 229
 230                 updated = updateFollowerLogInformation(followerLogInformation, appendEntriesReply);
 231             } else {
 232                 // TODO: When we find that the follower is out of sync with the
 233                 // Leader we simply decrement that followers next index by 1.
 234                 // Would it be possible to do better than this? The RAFT spec
 235                 // does not explicitly deal with it but may be something for us to
 236                 // think about.
 237
 238                 followerLogInformation.decrNextIndex();
 239             }
 240         }
 241
 242         // Now figure out if this reply warrants a change in the commitIndex
 243         // If there exists an N such that N > commitIndex, a majority
 244         // of matchIndex[i] ≥ N, and log[N].term == currentTerm:
 245         // set commitIndex = N (§5.3, §5.4).
 246         for (long N = context.getCommitIndex() + 1; ; N++) {
 247             int replicatedCount = 1;
 248
 249             for (FollowerLogInformation info : followerToLog.values()) {
 250                 if (info.getMatchIndex() >= N) {
 251                     replicatedCount++;
 252                 }
 253             }
 254
 255             if (replicatedCount >= minReplicationCount) {
 256                 ReplicatedLogEntry replicatedLogEntry = context.getReplicatedLog().get(N);
 257                 if (replicatedLogEntry != null &&
 258                     replicatedLogEntry.getTerm() == currentTerm()) {
 259                     context.setCommitIndex(N);
 260                 }
 261             } else {
 262                 break;
 263             }
 264         }
 265
 266         // Apply the change to the state machine
 267         if (context.getCommitIndex() > context.getLastApplied()) {
 268             if(LOG.isDebugEnabled()) {
 269                 LOG.debug("{}: handleAppendEntriesReply from {}: applying to log - commitIndex: {}, lastAppliedIndex: {}",
 270                         logName(), followerId, context.getCommitIndex(), context.getLastApplied());
 271             }
 272
 273             applyLogToStateMachine(context.getCommitIndex());
 274         }
 275
 276         if (!context.getSnapshotManager().isCapturing()) {
 277             purgeInMemoryLog();
 278         }
 279
 280         //Send the next log entry immediately, if possible, no need to wait for heartbeat to trigger that event
 281         sendUpdatesToFollower(followerId, followerLogInformation, false, !updated);
 282         return this;
 283     }
 284
 285     private boolean updateFollowerLogInformation(FollowerLogInformation followerLogInformation,
 286             AppendEntriesReply appendEntriesReply) {
 287         boolean updated = followerLogInformation.setMatchIndex(appendEntriesReply.getLogLastIndex());
 288         updated = followerLogInformation.setNextIndex(appendEntriesReply.getLogLastIndex() + 1) || updated;
 289
 290         if(updated && LOG.isDebugEnabled()) {
 291             LOG.debug("{}: handleAppendEntriesReply - FollowerLogInformation for {} updated: matchIndex: {}, nextIndex: {}",
 292                     logName(), followerLogInformation.getId(), followerLogInformation.getMatchIndex(),
 293                     followerLogInformation.getNextIndex());
 294         }
 295         return updated;
 296     }
 297
 298     private void purgeInMemoryLog() {
 299         //find the lowest index across followers which has been replicated to all.
 300         // lastApplied if there are no followers, so that we keep clearing the log for single-node
 301         // we would delete the in-mem log from that index on, in-order to minimize mem usage
 302         // we would also share this info thru AE with the followers so that they can delete their log entries as well.
 303         long minReplicatedToAllIndex = followerToLog.isEmpty() ? context.getLastApplied() : Long.MAX_VALUE;
 304         for (FollowerLogInformation info : followerToLog.values()) {
 305             minReplicatedToAllIndex = Math.min(minReplicatedToAllIndex, info.getMatchIndex());
 306         }
 307
 308         super.performSnapshotWithoutCapture(minReplicatedToAllIndex);
 309     }
 310
 311     @Override
 312     protected ClientRequestTracker removeClientRequestTracker(long logIndex) {
 313         final Iterator<ClientRequestTracker> it = trackerList.iterator();
 314         while (it.hasNext()) {
 315             final ClientRequestTracker t = it.next();
 316             if (t.getIndex() == logIndex) {
 317                 it.remove();
 318                 return t;
 319             }
 320         }
 321
 322         return null;
 323     }
 324
 325     @Override
 326     protected ClientRequestTracker findClientRequestTracker(long logIndex) {
 327         for (ClientRequestTracker tracker : trackerList) {
 328             if (tracker.getIndex() == logIndex) {
 329                 return tracker;
 330             }
 331         }
 332         return null;
 333     }
 334
 335     @Override
 336     protected RaftActorBehavior handleRequestVoteReply(ActorRef sender,
 337         RequestVoteReply requestVoteReply) {
 338         return this;
 339     }
 340
 341     protected void beforeSendHeartbeat(){}
 342
 343     @Override
 344     public RaftActorBehavior handleMessage(ActorRef sender, Object originalMessage) {
 345         Preconditions.checkNotNull(sender, "sender should not be null");
 346
 347         Object message = fromSerializableMessage(originalMessage);
 348
 349         if (message instanceof RaftRPC) {
 350             RaftRPC rpc = (RaftRPC) message;
 351             // If RPC request or response contains term T > currentTerm:
 352             // set currentTerm = T, convert to follower (§5.1)
 353             // This applies to all RPC messages and responses
 354             if (rpc.getTerm() > context.getTermInformation().getCurrentTerm()) {
 355                 LOG.debug("{}: Term {} in \"{}\" message is greater than leader's term {} - switching to Follower",
 356                         logName(), rpc.getTerm(), rpc, context.getTermInformation().getCurrentTerm());
 357
 358                 context.getTermInformation().updateAndPersist(rpc.getTerm(), null);
 359
 360                 return internalSwitchBehavior(RaftState.Follower);
 361             }
 362         }
 363
 364         if (message instanceof SendHeartBeat) {
 365             beforeSendHeartbeat();
 366             sendHeartBeat();
 367             scheduleHeartBeat(context.getConfigParams().getHeartBeatInterval());
 368             return this;
 369
 370         } else if(message instanceof SendInstallSnapshot) {
 371             // received from RaftActor
 372             setSnapshot(((SendInstallSnapshot) message).getSnapshot());
 373             sendInstallSnapshot();
 374
 375         } else if (message instanceof Replicate) {
 376             replicate((Replicate) message);
 377
 378         } else if (message instanceof InstallSnapshotReply){
 379             handleInstallSnapshotReply((InstallSnapshotReply) message);
 380
 381         }
 382
 383
 384         return super.handleMessage(sender, message);
 385     }
 386
 387     private void handleInstallSnapshotReply(InstallSnapshotReply reply) {
 388         LOG.debug("{}: handleInstallSnapshotReply: {}", logName(), reply);
 389
 390         String followerId = reply.getFollowerId();
 391         FollowerToSnapshot followerToSnapshot = mapFollowerToSnapshot.get(followerId);
 392
 393         if (followerToSnapshot == null) {
 394             LOG.error("{}: FollowerId {} in InstallSnapshotReply not known to Leader",
 395                     logName(), followerId);
 396             return;
 397         }
 398
 399         FollowerLogInformation followerLogInformation = followerToLog.get(followerId);
 400         followerLogInformation.markFollowerActive();
 401
 402         if (followerToSnapshot.getChunkIndex() == reply.getChunkIndex()) {
 403             boolean wasLastChunk = false;
 404             if (reply.isSuccess()) {
 405                 if(followerToSnapshot.isLastChunk(reply.getChunkIndex())) {
 406                     //this was the last chunk reply
 407                     if(LOG.isDebugEnabled()) {
 408                         LOG.debug("{}: InstallSnapshotReply received, " +
 409                                 "last chunk received, Chunk: {}. Follower: {} Setting nextIndex: {}",
 410                                 logName(), reply.getChunkIndex(), followerId,
 411                             context.getReplicatedLog().getSnapshotIndex() + 1
 412                         );
 413                     }
 414
 415                     long followerMatchIndex = snapshot.get().getLastIncludedIndex();
 416                     followerLogInformation.setMatchIndex(followerMatchIndex);
 417                     followerLogInformation.setNextIndex(followerMatchIndex + 1);
 418                     mapFollowerToSnapshot.remove(followerId);
 419
 420                     LOG.debug("{}: follower: {}, matchIndex set to {}, nextIndex set to {}",
 421                         logName(), followerId, followerLogInformation.getMatchIndex(),
 422                         followerLogInformation.getNextIndex());
 423
 424                     if (mapFollowerToSnapshot.isEmpty()) {
 425                         // once there are no pending followers receiving snapshots
 426                         // we can remove snapshot from the memory
 427                         setSnapshot(null);
 428                     }
 429                     wasLastChunk = true;
 430                     FollowerState followerState = followerLogInformation.getFollowerState();
 431                     if(followerState ==  FollowerState.VOTING_NOT_INITIALIZED){
 432                         UnInitializedFollowerSnapshotReply unInitFollowerSnapshotSuccess =
 433                                              new UnInitializedFollowerSnapshotReply(followerId);
 434                         context.getActor().tell(unInitFollowerSnapshotSuccess, context.getActor());
 435                         LOG.debug("Sent message UnInitializedFollowerSnapshotReply to self");
 436                     }
 437                 } else {
 438                     followerToSnapshot.markSendStatus(true);
 439                 }
 440             } else {
 441                 LOG.info("{}: InstallSnapshotReply received sending snapshot chunk failed, Will retry, Chunk: {}",
 442                         logName(), reply.getChunkIndex());
 443
 444                 followerToSnapshot.markSendStatus(false);
 445             }
 446
 447             if (wasLastChunk && !context.getSnapshotManager().isCapturing()) {
 448                 // Since the follower is now caught up try to purge the log.
 449                 purgeInMemoryLog();
 450             } else if (!wasLastChunk && followerToSnapshot.canSendNextChunk()) {
 451                 ActorSelection followerActor = context.getPeerActorSelection(followerId);
 452                 if(followerActor != null) {
 453                     sendSnapshotChunk(followerActor, followerId);
 454                 }
 455             }
 456
 457         } else {
 458             LOG.error("{}: Chunk index {} in InstallSnapshotReply from follower {} does not match expected index {}",
 459                     logName(), reply.getChunkIndex(), followerId,
 460                     followerToSnapshot.getChunkIndex());
 461
 462             if(reply.getChunkIndex() == INVALID_CHUNK_INDEX){
 463                 // Since the Follower did not find this index to be valid we should reset the follower snapshot
 464                 // so that Installing the snapshot can resume from the beginning
 465                 followerToSnapshot.reset();
 466             }
 467         }
 468     }
 469
 470     private void replicate(Replicate replicate) {
 471         long logIndex = replicate.getReplicatedLogEntry().getIndex();
 472
 473         LOG.debug("{}: Replicate message: identifier: {}, logIndex: {}", logName(),
 474                 replicate.getIdentifier(), logIndex);
 475
 476         // Create a tracker entry we will use this later to notify the
 477         // client actor
 478         trackerList.add(
 479             new ClientRequestTrackerImpl(replicate.getClientActor(),
 480                 replicate.getIdentifier(),
 481                 logIndex)
 482         );
 483
 484         boolean applyModificationToState = followerToLog.isEmpty()
 485                 || context.getRaftPolicy().applyModificationToStateBeforeConsensus();
 486
 487         if(applyModificationToState){
 488             context.setCommitIndex(logIndex);
 489             applyLogToStateMachine(logIndex);
 490         }
 491
 492         if (!followerToLog.isEmpty()) {
 493             sendAppendEntries(0, false);
 494         }
 495     }
 496
 497     private void sendAppendEntries(long timeSinceLastActivityInterval, boolean isHeartbeat) {
 498         // Send an AppendEntries to all followers
 499         for (Entry<String, FollowerLogInformation> e : followerToLog.entrySet()) {
 500             final String followerId = e.getKey();
 501             final FollowerLogInformation followerLogInformation = e.getValue();
 502             // This checks helps not to send a repeat message to the follower
 503             if(!followerLogInformation.isFollowerActive() ||
 504                     followerLogInformation.timeSinceLastActivity() >= timeSinceLastActivityInterval) {
 505                 sendUpdatesToFollower(followerId, followerLogInformation, true, isHeartbeat);
 506             }
 507         }
 508     }
 509
 510     /**
 511      *
 512      * This method checks if any update needs to be sent to the given follower. This includes append log entries,
 513      * sending next snapshot chunk, and initiating a snapshot.
 514      * @return true if any update is sent, false otherwise
 515      */
 516
 517     private void sendUpdatesToFollower(String followerId, FollowerLogInformation followerLogInformation,
 518                                        boolean sendHeartbeat, boolean isHeartbeat) {
 519
 520         ActorSelection followerActor = context.getPeerActorSelection(followerId);
 521         if (followerActor != null) {
 522             long followerNextIndex = followerLogInformation.getNextIndex();
 523             boolean isFollowerActive = followerLogInformation.isFollowerActive();
 524             boolean sendAppendEntries = false;
 525             List<ReplicatedLogEntry> entries = Collections.emptyList();
 526
 527             if (mapFollowerToSnapshot.get(followerId) != null) {
 528                 // if install snapshot is in process , then sent next chunk if possible
 529                 if (isFollowerActive && mapFollowerToSnapshot.get(followerId).canSendNextChunk()) {
 530                     sendSnapshotChunk(followerActor, followerId);
 531                 } else if(sendHeartbeat) {
 532                     // we send a heartbeat even if we have not received a reply for the last chunk
 533                     sendAppendEntries = true;
 534                 }
 535             } else {
 536                 long leaderLastIndex = context.getReplicatedLog().lastIndex();
 537                 long leaderSnapShotIndex = context.getReplicatedLog().getSnapshotIndex();
 538
 539                 if((!isHeartbeat && LOG.isDebugEnabled()) || LOG.isTraceEnabled()) {
 540                     LOG.debug("{}: Checking sendAppendEntries for follower {}: active: {}, followerNextIndex: {}, leaderLastIndex: {}, leaderSnapShotIndex: {}",
 541                             logName(), followerId, isFollowerActive, followerNextIndex, leaderLastIndex, leaderSnapShotIndex);
 542                 }
 543
 544                 if (isFollowerActive && context.getReplicatedLog().isPresent(followerNextIndex)) {
 545
 546                     LOG.debug("{}: sendAppendEntries: {} is present for follower {}", logName(),
 547                             followerNextIndex, followerId);
 548
 549                     if(followerLogInformation.okToReplicate()) {
 550                         // Try to send all the entries in the journal but not exceeding the max data size
 551                         // for a single AppendEntries message.
 552                         int maxEntries = (int) context.getReplicatedLog().size();
 553                         entries = context.getReplicatedLog().getFrom(followerNextIndex, maxEntries,
 554                                 context.getConfigParams().getSnapshotChunkSize());
 555                         sendAppendEntries = true;
 556                     }
 557                 } else if (isFollowerActive && followerNextIndex >= 0 &&
 558                     leaderLastIndex > followerNextIndex && !context.getSnapshotManager().isCapturing()) {
 559                     // if the followers next index is not present in the leaders log, and
 560                     // if the follower is just not starting and if leader's index is more than followers index
 561                     // then snapshot should be sent
 562
 563                     if (LOG.isDebugEnabled()) {
 564                         LOG.debug(String.format("%s: InitiateInstallSnapshot to follower: %s," +
 565                                     "follower-nextIndex: %d, leader-snapshot-index: %d,  " +
 566                                     "leader-last-index: %d", logName(), followerId,
 567                                     followerNextIndex, leaderSnapShotIndex, leaderLastIndex));
 568                     }
 569
 570                     // Send heartbeat to follower whenever install snapshot is initiated.
 571                     sendAppendEntries = true;
 572                     if (canInstallSnapshot(followerNextIndex)) {
 573                         initiateCaptureSnapshot(followerId);
 574                     }
 575
 576                 } else if(sendHeartbeat) {
 577                     // we send an AppendEntries, even if the follower is inactive
 578                     // in-order to update the followers timestamp, in case it becomes active again
 579                     sendAppendEntries = true;
 580                 }
 581
 582             }
 583
 584             if(sendAppendEntries) {
 585                 sendAppendEntriesToFollower(followerActor, followerNextIndex,
 586                         entries, followerId);
 587             }
 588         }
 589     }
 590
 591     private void sendAppendEntriesToFollower(ActorSelection followerActor, long followerNextIndex,
 592         List<ReplicatedLogEntry> entries, String followerId) {
 593         AppendEntries appendEntries = new AppendEntries(currentTerm(), context.getId(),
 594             prevLogIndex(followerNextIndex),
 595             prevLogTerm(followerNextIndex), entries,
 596             context.getCommitIndex(), super.getReplicatedToAllIndex(), context.getPayloadVersion());
 597
 598         if(!entries.isEmpty() || LOG.isTraceEnabled()) {
 599             LOG.debug("{}: Sending AppendEntries to follower {}: {}", logName(), followerId,
 600                     appendEntries);
 601         }
 602
 603         followerActor.tell(appendEntries.toSerializable(), actor());
 604     }
 605
 606     /**
 607      * Install Snapshot works as follows
 608      * 1. Leader initiates the capture snapshot by sending a CaptureSnapshot message to actor
 609      * 2. RaftActor on receipt of the CaptureSnapshotReply (from Shard), stores the received snapshot in the replicated log
 610      * and makes a call to Leader's handleMessage , with SendInstallSnapshot message.
 611      * 3. Leader , picks the snapshot from im-mem ReplicatedLog and sends it in chunks to the Follower
 612      * 4. On complete, Follower sends back a InstallSnapshotReply.
 613      * 5. On receipt of the InstallSnapshotReply for the last chunk, Leader marks the install complete for that follower
 614      * and replenishes the memory by deleting the snapshot in Replicated log.
 615      * 6. If another follower requires a snapshot and a snapshot has been collected (via CaptureSnapshotReply)
 616      * then send the existing snapshot in chunks to the follower.
 617      * @param followerId
 618      */
 619     public void initiateCaptureSnapshot(String followerId) {
 620         if (snapshot.isPresent()) {
 621             // if a snapshot is present in the memory, most likely another install is in progress
 622             // no need to capture snapshot.
 623             // This could happen if another follower needs an install when one is going on.
 624             final ActorSelection followerActor = context.getPeerActorSelection(followerId);
 625             sendSnapshotChunk(followerActor, followerId);
 626
 627
 628         } else {
 629             context.getSnapshotManager().captureToInstall(context.getReplicatedLog().last(),
 630                     this.getReplicatedToAllIndex(), followerId);
 631         }
 632     }
 633
 634     private boolean canInstallSnapshot(long nextIndex){
 635         // If the follower's nextIndex is -1 then we might as well send it a snapshot
 636         // Otherwise send it a snapshot only if the nextIndex is not present in the log but is present
 637         // in the snapshot
 638         return (nextIndex == -1 ||
 639                 (!context.getReplicatedLog().isPresent(nextIndex)
 640                         && context.getReplicatedLog().isInSnapshot(nextIndex)));
 641
 642     }
 643
 644
 645     private void sendInstallSnapshot() {
 646         LOG.debug("{}: sendInstallSnapshot", logName());
 647         for (Entry<String, FollowerLogInformation> e : followerToLog.entrySet()) {
 648             ActorSelection followerActor = context.getPeerActorSelection(e.getKey());
 649             FollowerLogInformation followerLogInfo = e.getValue();
 650
 651             if (followerActor != null) {
 652                 long nextIndex = e.getValue().getNextIndex();
 653                 if (followerLogInfo.getFollowerState() == FollowerState.VOTING_NOT_INITIALIZED ||
 654                         canInstallSnapshot(nextIndex)) {
 655                     sendSnapshotChunk(followerActor, e.getKey());
 656                 }
 657             }
 658         }
 659     }
 660
 661     /**
 662      *  Sends a snapshot chunk to a given follower
 663      *  InstallSnapshot should qualify as a heartbeat too.
 664      */
 665     private void sendSnapshotChunk(ActorSelection followerActor, String followerId) {
 666         try {
 667             if (snapshot.isPresent()) {
 668                 ByteString nextSnapshotChunk = getNextSnapshotChunk(followerId, snapshot.get().getSnapshotBytes());
 669
 670                 // Note: the previous call to getNextSnapshotChunk has the side-effect of adding
 671                 // followerId to the followerToSnapshot map.
 672                 FollowerToSnapshot followerToSnapshot = mapFollowerToSnapshot.get(followerId);
 673
 674                 followerActor.tell(
 675                     new InstallSnapshot(currentTerm(), context.getId(),
 676                         snapshot.get().getLastIncludedIndex(),
 677                         snapshot.get().getLastIncludedTerm(),
 678                         nextSnapshotChunk,
 679                         followerToSnapshot.incrementChunkIndex(),
 680                         followerToSnapshot.getTotalChunks(),
 681                         Optional.of(followerToSnapshot.getLastChunkHashCode())
 682                     ).toSerializable(),
 683                     actor()
 684                 );
 685
 686                 if(LOG.isDebugEnabled()) {
 687                     LOG.debug("{}: InstallSnapshot sent to follower {}, Chunk: {}/{}",
 688                             logName(), followerActor.path(), followerToSnapshot.getChunkIndex(),
 689                             followerToSnapshot.getTotalChunks());
 690                 }
 691             }
 692         } catch (IOException e) {
 693             LOG.error("{}: InstallSnapshot failed for Leader.", logName(), e);
 694         }
 695     }
 696
 697     /**
 698      * Acccepts snaphot as ByteString, enters into map for future chunks
 699      * creates and return a ByteString chunk
 700      */
 701     private ByteString getNextSnapshotChunk(String followerId, ByteString snapshotBytes) throws IOException {
 702         FollowerToSnapshot followerToSnapshot = mapFollowerToSnapshot.get(followerId);
 703         if (followerToSnapshot == null) {
 704             followerToSnapshot = new FollowerToSnapshot(snapshotBytes);
 705             mapFollowerToSnapshot.put(followerId, followerToSnapshot);
 706         }
 707         ByteString nextChunk = followerToSnapshot.getNextChunk();
 708
 709         LOG.debug("{}: next snapshot chunk size for follower {}: {}", logName(), followerId, nextChunk.size());
 710
 711         return nextChunk;
 712     }
 713
 714     private void sendHeartBeat() {
 715         if (!followerToLog.isEmpty()) {
 716             LOG.trace("{}: Sending heartbeat", logName());
 717             sendAppendEntries(context.getConfigParams().getHeartBeatInterval().toMillis(), true);
 718         }
 719     }
 720
 721     private void stopHeartBeat() {
 722         if (heartbeatSchedule != null && !heartbeatSchedule.isCancelled()) {
 723             heartbeatSchedule.cancel();
 724         }
 725     }
 726
 727     private void scheduleHeartBeat(FiniteDuration interval) {
 728         if (followerToLog.isEmpty()) {
 729             // Optimization - do not bother scheduling a heartbeat as there are
 730             // no followers
 731             return;
 732         }
 733
 734         stopHeartBeat();
 735
 736         // Schedule a heartbeat. When the scheduler triggers a SendHeartbeat
 737         // message is sent to itself.
 738         // Scheduling the heartbeat only once here because heartbeats do not
 739         // need to be sent if there are other messages being sent to the remote
 740         // actor.
 741         heartbeatSchedule = context.getActorSystem().scheduler().scheduleOnce(
 742             interval, context.getActor(), new SendHeartBeat(),
 743             context.getActorSystem().dispatcher(), context.getActor());
 744     }
 745
 746     @Override
 747     public void close() throws Exception {
 748         stopHeartBeat();
 749     }
 750
 751     @Override
 752     public String getLeaderId() {
 753         return context.getId();
 754     }
 755
 756     protected boolean isLeaderIsolated() {
 757         int minPresent = minIsolatedLeaderPeerCount;
 758         for (FollowerLogInformation followerLogInformation : followerToLog.values()) {
 759             if (followerLogInformation.isFollowerActive()) {
 760                 --minPresent;
 761                 if (minPresent == 0) {
 762                     break;
 763                 }
 764             }
 765         }
 766         return (minPresent != 0);
 767     }
 768
 769     /**
 770      * Encapsulates the snapshot bytestring and handles the logic of sending
 771      * snapshot chunks
 772      */
 773     protected class FollowerToSnapshot {
 774         private final ByteString snapshotBytes;
 775         private int offset = 0;
 776         // the next snapshot chunk is sent only if the replyReceivedForOffset matches offset
 777         private int replyReceivedForOffset;
 778         // if replyStatus is false, the previous chunk is attempted
 779         private boolean replyStatus = false;
 780         private int chunkIndex;
 781         private final int totalChunks;
 782         private int lastChunkHashCode = AbstractLeader.INITIAL_LAST_CHUNK_HASH_CODE;
 783         private int nextChunkHashCode = AbstractLeader.INITIAL_LAST_CHUNK_HASH_CODE;
 784
 785         public FollowerToSnapshot(ByteString snapshotBytes) {
 786             this.snapshotBytes = snapshotBytes;
 787             int size = snapshotBytes.size();
 788             totalChunks = ( size / context.getConfigParams().getSnapshotChunkSize()) +
 789                 ((size % context.getConfigParams().getSnapshotChunkSize()) > 0 ? 1 : 0);
 790             if(LOG.isDebugEnabled()) {
 791                 LOG.debug("{}: Snapshot {} bytes, total chunks to send:{}",
 792                         logName(), size, totalChunks);
 793             }
 794             replyReceivedForOffset = -1;
 795             chunkIndex = AbstractLeader.FIRST_CHUNK_INDEX;
 796         }
 797
 798         public ByteString getSnapshotBytes() {
 799             return snapshotBytes;
 800         }
 801
 802         public int incrementOffset() {
 803             if(replyStatus) {
 804                 // if prev chunk failed, we would want to sent the same chunk again
 805                 offset = offset + context.getConfigParams().getSnapshotChunkSize();
 806             }
 807             return offset;
 808         }
 809
 810         public int incrementChunkIndex() {
 811             if (replyStatus) {
 812                 // if prev chunk failed, we would want to sent the same chunk again
 813                 chunkIndex =  chunkIndex + 1;
 814             }
 815             return chunkIndex;
 816         }
 817
 818         public int getChunkIndex() {
 819             return chunkIndex;
 820         }
 821
 822         public int getTotalChunks() {
 823             return totalChunks;
 824         }
 825
 826         public boolean canSendNextChunk() {
 827             // we only send a false if a chunk is sent but we have not received a reply yet
 828             return replyReceivedForOffset == offset;
 829         }
 830
 831         public boolean isLastChunk(int chunkIndex) {
 832             return totalChunks == chunkIndex;
 833         }
 834
 835         public void markSendStatus(boolean success) {
 836             if (success) {
 837                 // if the chunk sent was successful
 838                 replyReceivedForOffset = offset;
 839                 replyStatus = true;
 840                 lastChunkHashCode = nextChunkHashCode;
 841             } else {
 842                 // if the chunk sent was failure
 843                 replyReceivedForOffset = offset;
 844                 replyStatus = false;
 845             }
 846         }
 847
 848         public ByteString getNextChunk() {
 849             int snapshotLength = getSnapshotBytes().size();
 850             int start = incrementOffset();
 851             int size = context.getConfigParams().getSnapshotChunkSize();
 852             if (context.getConfigParams().getSnapshotChunkSize() > snapshotLength) {
 853                 size = snapshotLength;
 854             } else {
 855                 if ((start + context.getConfigParams().getSnapshotChunkSize()) > snapshotLength) {
 856                     size = snapshotLength - start;
 857                 }
 858             }
 859
 860
 861             LOG.debug("{}: Next chunk: length={}, offset={},size={}", logName(),
 862                     snapshotLength, start, size);
 863
 864             ByteString substring = getSnapshotBytes().substring(start, start + size);
 865             nextChunkHashCode = substring.hashCode();
 866             return substring;
 867         }
 868
 869         /**
 870          * reset should be called when the Follower needs to be sent the snapshot from the beginning
 871          */
 872         public void reset(){
 873             offset = 0;
 874             replyStatus = false;
 875             replyReceivedForOffset = offset;
 876             chunkIndex = AbstractLeader.FIRST_CHUNK_INDEX;
 877             lastChunkHashCode = AbstractLeader.INITIAL_LAST_CHUNK_HASH_CODE;
 878         }
 879
 880         public int getLastChunkHashCode() {
 881             return lastChunkHashCode;
 882         }
 883     }
 884
 885     // called from example-actor for printing the follower-states
 886     public String printFollowerStates() {
 887         final StringBuilder sb = new StringBuilder();
 888
 889         sb.append('[');
 890         for (FollowerLogInformation followerLogInformation : followerToLog.values()) {
 891             sb.append('{');
 892             sb.append(followerLogInformation.getId());
 893             sb.append(" state:");
 894             sb.append(followerLogInformation.isFollowerActive());
 895             sb.append("},");
 896         }
 897         sb.append(']');
 898
 899         return sb.toString();
 900     }
 901
 902     @VisibleForTesting
 903     public FollowerLogInformation getFollower(String followerId) {
 904         return followerToLog.get(followerId);
 905     }
 906
 907     @VisibleForTesting
 908     protected void setFollowerSnapshot(String followerId, FollowerToSnapshot snapshot) {
 909         mapFollowerToSnapshot.put(followerId, snapshot);
 910     }
 911
 912     @VisibleForTesting
 913     public int followerSnapshotSize() {
 914         return mapFollowerToSnapshot.size();
 915     }
 916
 917     @VisibleForTesting
 918     public int followerLogSize() {
 919         return followerToLog.size();
 920     }
 921
 922     private static class SnapshotHolder {
 923         private final long lastIncludedTerm;
 924         private final long lastIncludedIndex;
 925         private final ByteString snapshotBytes;
 926
 927         SnapshotHolder(Snapshot snapshot) {
 928             this.lastIncludedTerm = snapshot.getLastAppliedTerm();
 929             this.lastIncludedIndex = snapshot.getLastAppliedIndex();
 930             this.snapshotBytes = ByteString.copyFrom(snapshot.getState());
 931         }
 932
 933         long getLastIncludedTerm() {
 934             return lastIncludedTerm;
 935         }
 936
 937         long getLastIncludedIndex() {
 938             return lastIncludedIndex;
 939         }
 940
 941         ByteString getSnapshotBytes() {
 942             return snapshotBytes;
 943         }
 944     }
 945 }