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.util.Collection;
  19 import java.util.Collections;
  20 import java.util.HashMap;
  21 import java.util.Iterator;
  22 import java.util.LinkedList;
  23 import java.util.List;
  24 import java.util.Map;
  25 import java.util.Map.Entry;
  26 import java.util.Queue;
  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 org.opendaylight.controller.cluster.raft.persisted.ServerConfigurationPayload;
  49 import scala.concurrent.duration.FiniteDuration;
  50
  51 /**
  52  * The behavior of a RaftActor when it is in the Leader state
  53  * <p/>
  54  * Leaders:
  55  * <ul>
  56  * <li> Upon election: send initial empty AppendEntries RPCs
  57  * (heartbeat) to each server; repeat during idle periods to
  58  * prevent election timeouts (§5.2)
  59  * <li> If command received from client: append entry to local log,
  60  * respond after entry applied to state machine (§5.3)
  61  * <li> If last log index ≥ nextIndex for a follower: send
  62  * AppendEntries RPC with log entries starting at nextIndex
  63  * <ul>
  64  * <li> If successful: update nextIndex and matchIndex for
  65  * follower (§5.3)
  66  * <li> If AppendEntries fails because of log inconsistency:
  67  * decrement nextIndex and retry (§5.3)
  68  * </ul>
  69  * <li> If there exists an N such that N > commitIndex, a majority
  70  * of matchIndex[i] ≥ N, and log[N].term == currentTerm:
  71  * set commitIndex = N (§5.3, §5.4).
  72  */
  73 public abstract class AbstractLeader extends AbstractRaftActorBehavior {
  74     private final Map<String, FollowerLogInformation> followerToLog = new HashMap<>();
  75
  76     /**
  77      * Lookup table for request contexts based on journal index. We could use a {@link Map} here, but we really
  78      * expect the entries to be modified in sequence, hence we open-code the lookup.
  79      *
  80      * TODO: Evaluate the use of ArrayDeque(), as that has lower memory overhead. Non-head removals are more costly,
  81      *       but we already expect those to be far from frequent.
  82      */
  83     private final Queue<ClientRequestTracker> trackers = new LinkedList<>();
  84
  85     private Cancellable heartbeatSchedule = null;
  86     private Optional<SnapshotHolder> snapshot = Optional.absent();
  87     private int minReplicationCount;
  88
  89     protected AbstractLeader(RaftActorContext context, RaftState state,
  90             @Nullable AbstractLeader initializeFromLeader) {
  91         super(context, state);
  92
  93         if(initializeFromLeader != null) {
  94             followerToLog.putAll(initializeFromLeader.followerToLog);
  95             snapshot = initializeFromLeader.snapshot;
  96             trackers.addAll(initializeFromLeader.trackers);
  97         } else {
  98             for(PeerInfo peerInfo: context.getPeers()) {
  99                 FollowerLogInformation followerLogInformation = new FollowerLogInformationImpl(peerInfo, -1, context);
 100                 followerToLog.put(peerInfo.getId(), followerLogInformation);
 101             }
 102         }
 103
 104         LOG.debug("{}: Election: Leader has following peers: {}", logName(), getFollowerIds());
 105
 106         updateMinReplicaCount();
 107
 108         // Immediately schedule a heartbeat
 109         // Upon election: send initial empty AppendEntries RPCs
 110         // (heartbeat) to each server; repeat during idle periods to
 111         // prevent election timeouts (§5.2)
 112         sendAppendEntries(0, false);
 113
 114         // It is important to schedule this heartbeat here
 115         scheduleHeartBeat(context.getConfigParams().getHeartBeatInterval());
 116     }
 117
 118     protected AbstractLeader(RaftActorContext context, RaftState state) {
 119         this(context, state, null);
 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     @VisibleForTesting
 177     boolean hasSnapshot() {
 178         return snapshot.isPresent();
 179     }
 180
 181     @Override
 182     protected RaftActorBehavior handleAppendEntries(ActorRef sender,
 183         AppendEntries appendEntries) {
 184
 185         LOG.debug("{}: handleAppendEntries: {}", logName(), appendEntries);
 186
 187         return this;
 188     }
 189
 190     @Override
 191     protected RaftActorBehavior handleAppendEntriesReply(ActorRef sender, AppendEntriesReply appendEntriesReply) {
 192         if(LOG.isTraceEnabled()) {
 193             LOG.trace("{}: handleAppendEntriesReply: {}", logName(), appendEntriesReply);
 194         }
 195
 196         // Update the FollowerLogInformation
 197         String followerId = appendEntriesReply.getFollowerId();
 198         FollowerLogInformation followerLogInformation = followerToLog.get(followerId);
 199
 200         if(followerLogInformation == null){
 201             LOG.error("{}: handleAppendEntriesReply - unknown follower {}", logName(), followerId);
 202             return this;
 203         }
 204
 205         if(followerLogInformation.timeSinceLastActivity() >
 206                 context.getConfigParams().getElectionTimeOutInterval().toMillis()) {
 207             LOG.warn("{} : handleAppendEntriesReply delayed beyond election timeout, " +
 208                             "appendEntriesReply : {}, timeSinceLastActivity : {}, lastApplied : {}, commitIndex : {}",
 209                     logName(), appendEntriesReply, followerLogInformation.timeSinceLastActivity(),
 210                     context.getLastApplied(), context.getCommitIndex());
 211         }
 212
 213         followerLogInformation.markFollowerActive();
 214         followerLogInformation.setPayloadVersion(appendEntriesReply.getPayloadVersion());
 215         followerLogInformation.setRaftVersion(appendEntriesReply.getRaftVersion());
 216
 217         long followerLastLogIndex = appendEntriesReply.getLogLastIndex();
 218         long followersLastLogTermInLeadersLog = getLogEntryTerm(followerLastLogIndex);
 219         boolean updated = false;
 220         if(appendEntriesReply.getLogLastIndex() > context.getReplicatedLog().lastIndex()) {
 221             // The follower's log is actually ahead of the leader's log. Normally this doesn't happen
 222             // in raft as a node cannot become leader if it's log is behind another's. However, the
 223             // non-voting semantics deviate a bit from raft. Only voting members participate in
 224             // elections and can become leader so it's possible for a non-voting follower to be ahead
 225             // of the leader. This can happen if persistence is disabled and all voting members are
 226             // restarted. In this case, the voting leader will start out with an empty log however
 227             // the non-voting followers still retain the previous data in memory. On the first
 228             // AppendEntries, the non-voting follower returns a successful reply b/c the prevLogIndex
 229             // sent by the leader is -1 and thus the integrity checks pass. However the follower's returned
 230             // lastLogIndex may be higher in which case we want to reset the follower by installing a
 231             // snapshot. It's also possible that the follower's last log index is behind the leader's.
 232             // However in this case the log terms won't match and the logs will conflict - this is handled
 233             // elsewhere.
 234             LOG.debug("{}: handleAppendEntriesReply: follower {} lastIndex {} is ahead of our lastIndex {} - forcing install snaphot",
 235                     logName(), followerLogInformation.getId(), appendEntriesReply.getLogLastIndex(),
 236                     context.getReplicatedLog().lastIndex());
 237
 238             followerLogInformation.setMatchIndex(-1);
 239             followerLogInformation.setNextIndex(-1);
 240
 241             initiateCaptureSnapshot(followerId);
 242
 243             updated = true;
 244         } else if (appendEntriesReply.isSuccess()) {
 245             if (followerLastLogIndex >= 0 && followersLastLogTermInLeadersLog >= 0 &&
 246                     followersLastLogTermInLeadersLog != appendEntriesReply.getLogLastTerm()) {
 247                 // The follower's last entry is present in the leader's journal but the terms don't match so the
 248                 // follower has a conflicting entry. Since the follower didn't report that it's out of sync, this means
 249                 // either the previous leader entry sent didn't conflict or the previous leader entry is in the snapshot
 250                 // and no longer in the journal. Either way, we set the follower's next index to 1 less than the last
 251                 // index reported by the follower. For the former case, the leader will send all entries starting with
 252                 // the previous follower's index and the follower will remove and replace the conflicting entries as
 253                 // needed. For the latter, the leader will initiate an install snapshot.
 254
 255                 followerLogInformation.setNextIndex(followerLastLogIndex - 1);
 256                 updated = true;
 257
 258                 LOG.debug("{}: handleAppendEntriesReply: follower {} last log term {} for index {} conflicts with the " +
 259                           "leader's {} - set the follower's next index to {}",
 260                         logName(), followerId, appendEntriesReply.getLogLastTerm(), appendEntriesReply.getLogLastIndex(),
 261                         followersLastLogTermInLeadersLog, followerLogInformation.getNextIndex());
 262             } else {
 263                 updated = updateFollowerLogInformation(followerLogInformation, appendEntriesReply);
 264             }
 265         } else {
 266             LOG.debug("{}: handleAppendEntriesReply: received unsuccessful reply: {}", logName(), appendEntriesReply);
 267
 268             if(appendEntriesReply.isForceInstallSnapshot()) {
 269                 // Reset the followers match and next index. This is to signal that this follower has nothing
 270                 // in common with this Leader and so would require a snapshot to be installed
 271                 followerLogInformation.setMatchIndex(-1);
 272                 followerLogInformation.setNextIndex(-1);
 273
 274                 // Force initiate a snapshot capture
 275                 initiateCaptureSnapshot(followerId);
 276             } else if(followerLastLogIndex < 0 || followersLastLogTermInLeadersLog >= 0 &&
 277                     followersLastLogTermInLeadersLog == appendEntriesReply.getLogLastTerm()) {
 278                 // The follower's log is empty or the last entry is present in the leader's journal
 279                 // and the terms match so the follower is just behind the leader's journal from
 280                 // the last snapshot, if any. We'll catch up the follower quickly by starting at the
 281                 // follower's last log index.
 282
 283                 updated = updateFollowerLogInformation(followerLogInformation, appendEntriesReply);
 284             } else {
 285                 // The follower's log conflicts with leader's log so decrement follower's next index by 1
 286                 // in an attempt to find where the logs match.
 287
 288                 followerLogInformation.decrNextIndex();
 289                 updated = true;
 290
 291                 LOG.debug("{}: follower's last log term {} conflicts with the leader's {} - dec next index to {}",
 292                         logName(), appendEntriesReply.getLogLastTerm(), followersLastLogTermInLeadersLog,
 293                         followerLogInformation.getNextIndex());
 294             }
 295         }
 296
 297         // Now figure out if this reply warrants a change in the commitIndex
 298         // If there exists an N such that N > commitIndex, a majority
 299         // of matchIndex[i] ≥ N, and log[N].term == currentTerm:
 300         // set commitIndex = N (§5.3, §5.4).
 301         if(LOG.isTraceEnabled()) {
 302             LOG.trace("{}: handleAppendEntriesReply from {}: commitIndex: {}, lastAppliedIndex: {}, currentTerm: {}",
 303                     logName(), followerId, context.getCommitIndex(), context.getLastApplied(), currentTerm());
 304         }
 305
 306         for (long N = context.getCommitIndex() + 1; ; N++) {
 307             int replicatedCount = 1;
 308
 309             LOG.trace("{}: checking Nth index {}", logName(), N);
 310             for (FollowerLogInformation info : followerToLog.values()) {
 311                 final PeerInfo peerInfo = context.getPeerInfo(info.getId());
 312                 if(info.getMatchIndex() >= N && peerInfo != null && peerInfo.isVoting()) {
 313                     replicatedCount++;
 314                 } else if(LOG.isTraceEnabled()) {
 315                     LOG.trace("{}: Not counting follower {} - matchIndex: {}, {}", logName(), info.getId(),
 316                             info.getMatchIndex(), peerInfo);
 317                 }
 318             }
 319
 320             if(LOG.isTraceEnabled()) {
 321                 LOG.trace("{}: replicatedCount {}, minReplicationCount: {}", logName(), replicatedCount, minReplicationCount);
 322             }
 323
 324             if (replicatedCount >= minReplicationCount) {
 325                 ReplicatedLogEntry replicatedLogEntry = context.getReplicatedLog().get(N);
 326                 if (replicatedLogEntry == null) {
 327                     LOG.debug("{}: ReplicatedLogEntry not found for index {} - snapshotIndex: {}, journal size: {}",
 328                             logName(), N, context.getReplicatedLog().getSnapshotIndex(), context.getReplicatedLog().size());
 329                     break;
 330                 }
 331
 332                 // Don't update the commit index if the log entry is from a previous term, as per §5.4.1:
 333                 // "Raft never commits log entries from previous terms by counting replicas".
 334                 // However we keep looping so we can make progress when new entries in the current term
 335                 // reach consensus, as per §5.4.1: "once an entry from the current term is committed by
 336                 // counting replicas, then all prior entries are committed indirectly".
 337                 if (replicatedLogEntry.getTerm() == currentTerm()) {
 338                     LOG.trace("{}: Setting commit index to {}", logName(), N);
 339                     context.setCommitIndex(N);
 340                 } else {
 341                     LOG.debug("{}: Not updating commit index to {} - retrieved log entry with index {}, term {} does not match the current term {}",
 342                             logName(), N, replicatedLogEntry.getIndex(), replicatedLogEntry.getTerm(), currentTerm());
 343                 }
 344             } else {
 345                 LOG.trace("{}: minReplicationCount not reached, actual {} - breaking", logName(), replicatedCount);
 346                 break;
 347             }
 348         }
 349
 350         // Apply the change to the state machine
 351         if (context.getCommitIndex() > context.getLastApplied()) {
 352             if(LOG.isDebugEnabled()) {
 353                 LOG.debug("{}: handleAppendEntriesReply from {}: applying to log - commitIndex: {}, lastAppliedIndex: {}",
 354                         logName(), followerId, context.getCommitIndex(), context.getLastApplied());
 355             }
 356
 357             applyLogToStateMachine(context.getCommitIndex());
 358         }
 359
 360         if (!context.getSnapshotManager().isCapturing()) {
 361             purgeInMemoryLog();
 362         }
 363
 364         //Send the next log entry immediately, if possible, no need to wait for heartbeat to trigger that event
 365         sendUpdatesToFollower(followerId, followerLogInformation, false, !updated);
 366
 367         return this;
 368     }
 369
 370     private boolean updateFollowerLogInformation(FollowerLogInformation followerLogInformation,
 371             AppendEntriesReply appendEntriesReply) {
 372         boolean updated = followerLogInformation.setMatchIndex(appendEntriesReply.getLogLastIndex());
 373         updated = followerLogInformation.setNextIndex(appendEntriesReply.getLogLastIndex() + 1) || updated;
 374
 375         if(updated && LOG.isDebugEnabled()) {
 376             LOG.debug("{}: handleAppendEntriesReply - FollowerLogInformation for {} updated: matchIndex: {}, nextIndex: {}",
 377                     logName(), followerLogInformation.getId(), followerLogInformation.getMatchIndex(),
 378                     followerLogInformation.getNextIndex());
 379         }
 380         return updated;
 381     }
 382
 383     private void purgeInMemoryLog() {
 384         //find the lowest index across followers which has been replicated to all.
 385         // lastApplied if there are no followers, so that we keep clearing the log for single-node
 386         // we would delete the in-mem log from that index on, in-order to minimize mem usage
 387         // we would also share this info thru AE with the followers so that they can delete their log entries as well.
 388         long minReplicatedToAllIndex = followerToLog.isEmpty() ? context.getLastApplied() : Long.MAX_VALUE;
 389         for (FollowerLogInformation info : followerToLog.values()) {
 390             minReplicatedToAllIndex = Math.min(minReplicatedToAllIndex, info.getMatchIndex());
 391         }
 392
 393         super.performSnapshotWithoutCapture(minReplicatedToAllIndex);
 394     }
 395
 396     @Override
 397     protected ClientRequestTracker removeClientRequestTracker(long logIndex) {
 398         final Iterator<ClientRequestTracker> it = trackers.iterator();
 399         while (it.hasNext()) {
 400             final ClientRequestTracker t = it.next();
 401             if (t.getIndex() == logIndex) {
 402                 it.remove();
 403                 return t;
 404             }
 405         }
 406
 407         return null;
 408     }
 409
 410     @Override
 411     protected RaftActorBehavior handleRequestVoteReply(ActorRef sender,
 412         RequestVoteReply requestVoteReply) {
 413         return this;
 414     }
 415
 416     protected void beforeSendHeartbeat(){}
 417
 418     @Override
 419     public RaftActorBehavior handleMessage(ActorRef sender, Object message) {
 420         Preconditions.checkNotNull(sender, "sender should not be null");
 421
 422         if (message instanceof RaftRPC) {
 423             RaftRPC rpc = (RaftRPC) message;
 424             // If RPC request or response contains term T > currentTerm:
 425             // set currentTerm = T, convert to follower (§5.1)
 426             // This applies to all RPC messages and responses
 427             if (rpc.getTerm() > context.getTermInformation().getCurrentTerm()) {
 428                 LOG.debug("{}: Term {} in \"{}\" message is greater than leader's term {} - switching to Follower",
 429                         logName(), rpc.getTerm(), rpc, context.getTermInformation().getCurrentTerm());
 430
 431                 context.getTermInformation().updateAndPersist(rpc.getTerm(), null);
 432
 433                 return internalSwitchBehavior(RaftState.Follower);
 434             }
 435         }
 436
 437         if (message instanceof SendHeartBeat) {
 438             beforeSendHeartbeat();
 439             sendHeartBeat();
 440             scheduleHeartBeat(context.getConfigParams().getHeartBeatInterval());
 441         } else if(message instanceof SendInstallSnapshot) {
 442             // received from RaftActor
 443             setSnapshot(((SendInstallSnapshot) message).getSnapshot());
 444             sendInstallSnapshot();
 445         } else if (message instanceof Replicate) {
 446             replicate((Replicate) message);
 447         } else if (message instanceof InstallSnapshotReply) {
 448             handleInstallSnapshotReply((InstallSnapshotReply) message);
 449         } else {
 450             return super.handleMessage(sender, message);
 451         }
 452
 453         return this;
 454     }
 455
 456     private void handleInstallSnapshotReply(InstallSnapshotReply reply) {
 457         LOG.debug("{}: handleInstallSnapshotReply: {}", logName(), reply);
 458
 459         String followerId = reply.getFollowerId();
 460         FollowerLogInformation followerLogInformation = followerToLog.get(followerId);
 461         if(followerLogInformation == null) {
 462             // This can happen during AddServer if it times out.
 463             LOG.error("{}: FollowerLogInformation not found for follower {} in InstallSnapshotReply",
 464                     logName(), followerId);
 465             return;
 466         }
 467
 468         LeaderInstallSnapshotState installSnapshotState = followerLogInformation.getInstallSnapshotState();
 469         if (installSnapshotState == null) {
 470             LOG.error("{}: LeaderInstallSnapshotState not found for follower {} in InstallSnapshotReply",
 471                     logName(), followerId);
 472             return;
 473         }
 474
 475         followerLogInformation.markFollowerActive();
 476
 477         if (installSnapshotState.getChunkIndex() == reply.getChunkIndex()) {
 478             boolean wasLastChunk = false;
 479             if (reply.isSuccess()) {
 480                 if(installSnapshotState.isLastChunk(reply.getChunkIndex())) {
 481                     //this was the last chunk reply
 482                     if(LOG.isDebugEnabled()) {
 483                         LOG.debug("{}: InstallSnapshotReply received, " +
 484                                 "last chunk received, Chunk: {}. Follower: {} Setting nextIndex: {}",
 485                                 logName(), reply.getChunkIndex(), followerId,
 486                             context.getReplicatedLog().getSnapshotIndex() + 1
 487                         );
 488                     }
 489
 490                     long followerMatchIndex = snapshot.get().getLastIncludedIndex();
 491                     followerLogInformation.setMatchIndex(followerMatchIndex);
 492                     followerLogInformation.setNextIndex(followerMatchIndex + 1);
 493                     followerLogInformation.clearLeaderInstallSnapshotState();
 494
 495                     LOG.debug("{}: follower: {}, matchIndex set to {}, nextIndex set to {}",
 496                         logName(), followerId, followerLogInformation.getMatchIndex(),
 497                         followerLogInformation.getNextIndex());
 498
 499                     if (!anyFollowersInstallingSnapshot()) {
 500                         // once there are no pending followers receiving snapshots
 501                         // we can remove snapshot from the memory
 502                         setSnapshot(null);
 503                     }
 504
 505                     wasLastChunk = true;
 506                     if(context.getPeerInfo(followerId).getVotingState() == VotingState.VOTING_NOT_INITIALIZED){
 507                         UnInitializedFollowerSnapshotReply unInitFollowerSnapshotSuccess =
 508                                              new UnInitializedFollowerSnapshotReply(followerId);
 509                         context.getActor().tell(unInitFollowerSnapshotSuccess, context.getActor());
 510                         LOG.debug("Sent message UnInitializedFollowerSnapshotReply to self");
 511                     }
 512                 } else {
 513                     installSnapshotState.markSendStatus(true);
 514                 }
 515             } else {
 516                 LOG.info("{}: InstallSnapshotReply received sending snapshot chunk failed, Will retry, Chunk: {}",
 517                         logName(), reply.getChunkIndex());
 518
 519                 installSnapshotState.markSendStatus(false);
 520             }
 521
 522             if (wasLastChunk && !context.getSnapshotManager().isCapturing()) {
 523                 // Since the follower is now caught up try to purge the log.
 524                 purgeInMemoryLog();
 525             } else if (!wasLastChunk && installSnapshotState.canSendNextChunk()) {
 526                 ActorSelection followerActor = context.getPeerActorSelection(followerId);
 527                 if(followerActor != null) {
 528                     sendSnapshotChunk(followerActor, followerLogInformation);
 529                 }
 530             }
 531
 532         } else {
 533             LOG.error("{}: Chunk index {} in InstallSnapshotReply from follower {} does not match expected index {}",
 534                     logName(), reply.getChunkIndex(), followerId,
 535                     installSnapshotState.getChunkIndex());
 536
 537             if(reply.getChunkIndex() == LeaderInstallSnapshotState.INVALID_CHUNK_INDEX){
 538                 // Since the Follower did not find this index to be valid we should reset the follower snapshot
 539                 // so that Installing the snapshot can resume from the beginning
 540                 installSnapshotState.reset();
 541             }
 542         }
 543     }
 544
 545     private boolean anyFollowersInstallingSnapshot() {
 546         for(FollowerLogInformation info: followerToLog.values()) {
 547             if(info.getInstallSnapshotState() != null) {
 548                 return true;
 549             }
 550
 551         }
 552
 553         return false;
 554     }
 555
 556     private void replicate(Replicate replicate) {
 557         long logIndex = replicate.getReplicatedLogEntry().getIndex();
 558
 559         LOG.debug("{}: Replicate message: identifier: {}, logIndex: {}, payload: {}", logName(),
 560                 replicate.getIdentifier(), logIndex, replicate.getReplicatedLogEntry().getData().getClass());
 561
 562         // Create a tracker entry we will use this later to notify the
 563         // client actor
 564         if(replicate.getClientActor() != null) {
 565             trackers.add(new ClientRequestTrackerImpl(replicate.getClientActor(), replicate.getIdentifier(),
 566                     logIndex));
 567         }
 568
 569         boolean applyModificationToState = !context.anyVotingPeers()
 570                 || context.getRaftPolicy().applyModificationToStateBeforeConsensus();
 571
 572         if(applyModificationToState){
 573             context.setCommitIndex(logIndex);
 574             applyLogToStateMachine(logIndex);
 575         }
 576
 577         if (!followerToLog.isEmpty()) {
 578             sendAppendEntries(0, false);
 579         }
 580     }
 581
 582     protected void sendAppendEntries(long timeSinceLastActivityInterval, boolean isHeartbeat) {
 583         // Send an AppendEntries to all followers
 584         for (Entry<String, FollowerLogInformation> e : followerToLog.entrySet()) {
 585             final String followerId = e.getKey();
 586             final FollowerLogInformation followerLogInformation = e.getValue();
 587             // This checks helps not to send a repeat message to the follower
 588             if(!followerLogInformation.isFollowerActive() ||
 589                     followerLogInformation.timeSinceLastActivity() >= timeSinceLastActivityInterval) {
 590                 sendUpdatesToFollower(followerId, followerLogInformation, true, isHeartbeat);
 591             }
 592         }
 593     }
 594
 595     /**
 596      *
 597      * This method checks if any update needs to be sent to the given follower. This includes append log entries,
 598      * sending next snapshot chunk, and initiating a snapshot.
 599      * @return true if any update is sent, false otherwise
 600      */
 601
 602     private void sendUpdatesToFollower(String followerId, FollowerLogInformation followerLogInformation,
 603                                        boolean sendHeartbeat, boolean isHeartbeat) {
 604
 605         ActorSelection followerActor = context.getPeerActorSelection(followerId);
 606         if (followerActor != null) {
 607             long followerNextIndex = followerLogInformation.getNextIndex();
 608             boolean isFollowerActive = followerLogInformation.isFollowerActive();
 609             boolean sendAppendEntries = false;
 610             List<ReplicatedLogEntry> entries = Collections.emptyList();
 611
 612             LeaderInstallSnapshotState installSnapshotState = followerLogInformation.getInstallSnapshotState();
 613             if (installSnapshotState != null) {
 614                 // if install snapshot is in process , then sent next chunk if possible
 615                 if (isFollowerActive && installSnapshotState.canSendNextChunk()) {
 616                     sendSnapshotChunk(followerActor, followerLogInformation);
 617                 } else if(sendHeartbeat) {
 618                     // we send a heartbeat even if we have not received a reply for the last chunk
 619                     sendAppendEntries = true;
 620                 }
 621             } else {
 622                 long leaderLastIndex = context.getReplicatedLog().lastIndex();
 623                 long leaderSnapShotIndex = context.getReplicatedLog().getSnapshotIndex();
 624
 625                 if((!isHeartbeat && LOG.isDebugEnabled()) || LOG.isTraceEnabled()) {
 626                     LOG.debug("{}: Checking sendAppendEntries for follower {}: active: {}, followerNextIndex: {}, leaderLastIndex: {}, leaderSnapShotIndex: {}",
 627                             logName(), followerId, isFollowerActive, followerNextIndex, leaderLastIndex, leaderSnapShotIndex);
 628                 }
 629
 630                 if (isFollowerActive && context.getReplicatedLog().isPresent(followerNextIndex)) {
 631
 632                     LOG.debug("{}: sendAppendEntries: {} is present for follower {}", logName(),
 633                             followerNextIndex, followerId);
 634
 635                     if(followerLogInformation.okToReplicate()) {
 636                         // Try to send all the entries in the journal but not exceeding the max data size
 637                         // for a single AppendEntries message.
 638                         int maxEntries = (int) context.getReplicatedLog().size();
 639                         entries = context.getReplicatedLog().getFrom(followerNextIndex, maxEntries,
 640                                 context.getConfigParams().getSnapshotChunkSize());
 641                         sendAppendEntries = true;
 642                     }
 643                 } else if (isFollowerActive && followerNextIndex >= 0 &&
 644                     leaderLastIndex > followerNextIndex && !context.getSnapshotManager().isCapturing()) {
 645                     // if the followers next index is not present in the leaders log, and
 646                     // if the follower is just not starting and if leader's index is more than followers index
 647                     // then snapshot should be sent
 648
 649                     if (LOG.isDebugEnabled()) {
 650                         LOG.debug(String.format("%s: InitiateInstallSnapshot to follower: %s, " +
 651                                     "follower-nextIndex: %d, leader-snapshot-index: %d,  " +
 652                                     "leader-last-index: %d", logName(), followerId,
 653                                     followerNextIndex, leaderSnapShotIndex, leaderLastIndex));
 654                     }
 655
 656                     // Send heartbeat to follower whenever install snapshot is initiated.
 657                     sendAppendEntries = true;
 658                     if (canInstallSnapshot(followerNextIndex)) {
 659                         initiateCaptureSnapshot(followerId);
 660                     }
 661
 662                 } else if(sendHeartbeat) {
 663                     // we send an AppendEntries, even if the follower is inactive
 664                     // in-order to update the followers timestamp, in case it becomes active again
 665                     sendAppendEntries = true;
 666                 }
 667
 668             }
 669
 670             if(sendAppendEntries) {
 671                 sendAppendEntriesToFollower(followerActor, entries, followerLogInformation);
 672             }
 673         }
 674     }
 675
 676     private void sendAppendEntriesToFollower(ActorSelection followerActor, List<ReplicatedLogEntry> entries,
 677             FollowerLogInformation followerLogInformation) {
 678         // In certain cases outlined below we don't want to send the actual commit index to prevent the follower from
 679         // possibly committing and applying conflicting entries (those with same index, different term) from a prior
 680         // term that weren't replicated to a majority, which would be a violation of raft.
 681         //     - if the follower isn't active. In this case we don't know the state of the follower and we send an
 682         //       empty AppendEntries as a heart beat to prevent election.
 683         //     - if we're in the process of installing a snapshot. In this case we don't send any new entries but still
 684         //       need to send AppendEntries to prevent election.
 685         boolean isInstallingSnaphot = followerLogInformation.getInstallSnapshotState() != null;
 686         long leaderCommitIndex = isInstallingSnaphot || !followerLogInformation.isFollowerActive() ? -1 :
 687             context.getCommitIndex();
 688
 689         long followerNextIndex = followerLogInformation.getNextIndex();
 690         AppendEntries appendEntries = new AppendEntries(currentTerm(), context.getId(),
 691             getLogEntryIndex(followerNextIndex - 1),
 692             getLogEntryTerm(followerNextIndex - 1), entries,
 693             leaderCommitIndex, super.getReplicatedToAllIndex(), context.getPayloadVersion());
 694
 695         if(!entries.isEmpty() || LOG.isTraceEnabled()) {
 696             LOG.debug("{}: Sending AppendEntries to follower {}: {}", logName(), followerLogInformation.getId(),
 697                     appendEntries);
 698         }
 699
 700         followerActor.tell(appendEntries, actor());
 701     }
 702
 703     /**
 704      * Initiates a snapshot capture to install on a follower.
 705      *
 706      * Install Snapshot works as follows
 707      *   1. Leader initiates the capture snapshot by calling createSnapshot on the RaftActor.
 708      *   2. On receipt of the CaptureSnapshotReply message, the RaftActor persists the snapshot and makes a call to
 709      *      the Leader's handleMessage with a SendInstallSnapshot message.
 710      *   3. The Leader obtains and stores the Snapshot from the SendInstallSnapshot message and sends it in chunks to
 711      *      the Follower via InstallSnapshot messages.
 712      *   4. For each chunk, the Follower sends back an InstallSnapshotReply.
 713      *   5. On receipt of the InstallSnapshotReply for the last chunk, the Leader marks the install complete for that
 714      *      follower.
 715      *   6. If another follower requires a snapshot and a snapshot has been collected (via SendInstallSnapshot)
 716      *      then send the existing snapshot in chunks to the follower.
 717      *
 718      * @param followerId the id of the follower.
 719      * @return true if capture was initiated, false otherwise.
 720      */
 721     public boolean initiateCaptureSnapshot(String followerId) {
 722         FollowerLogInformation followerLogInfo = followerToLog.get(followerId);
 723         if (snapshot.isPresent()) {
 724             // If a snapshot is present in the memory, most likely another install is in progress no need to capture
 725             // snapshot. This could happen if another follower needs an install when one is going on.
 726             final ActorSelection followerActor = context.getPeerActorSelection(followerId);
 727
 728             // Note: sendSnapshotChunk will set the LeaderInstallSnapshotState.
 729             sendSnapshotChunk(followerActor, followerLogInfo);
 730             return true;
 731         } else {
 732             boolean captureInitiated = context.getSnapshotManager().captureToInstall(context.getReplicatedLog().last(),
 733                     this.getReplicatedToAllIndex(), followerId);
 734             if(captureInitiated) {
 735                 followerLogInfo.setLeaderInstallSnapshotState(new LeaderInstallSnapshotState(
 736                         context.getConfigParams().getSnapshotChunkSize(), logName()));
 737             }
 738
 739             return captureInitiated;
 740         }
 741     }
 742
 743     private boolean canInstallSnapshot(long nextIndex){
 744         // If the follower's nextIndex is -1 then we might as well send it a snapshot
 745         // Otherwise send it a snapshot only if the nextIndex is not present in the log but is present
 746         // in the snapshot
 747         return nextIndex == -1 ||
 748                 (!context.getReplicatedLog().isPresent(nextIndex)
 749                         && context.getReplicatedLog().isInSnapshot(nextIndex));
 750
 751     }
 752
 753
 754     private void sendInstallSnapshot() {
 755         LOG.debug("{}: sendInstallSnapshot", logName());
 756         for (Entry<String, FollowerLogInformation> e : followerToLog.entrySet()) {
 757             String followerId = e.getKey();
 758             ActorSelection followerActor = context.getPeerActorSelection(followerId);
 759             FollowerLogInformation followerLogInfo = e.getValue();
 760
 761             if (followerActor != null) {
 762                 long nextIndex = followerLogInfo.getNextIndex();
 763                 if (followerLogInfo.getInstallSnapshotState() != null ||
 764                         context.getPeerInfo(followerId).getVotingState() == VotingState.VOTING_NOT_INITIALIZED ||
 765                         canInstallSnapshot(nextIndex)) {
 766                     sendSnapshotChunk(followerActor, followerLogInfo);
 767                 }
 768             }
 769         }
 770     }
 771
 772     /**
 773      *  Sends a snapshot chunk to a given follower
 774      *  InstallSnapshot should qualify as a heartbeat too.
 775      */
 776     private void sendSnapshotChunk(ActorSelection followerActor, FollowerLogInformation followerLogInfo) {
 777         if (snapshot.isPresent()) {
 778             LeaderInstallSnapshotState installSnapshotState = followerLogInfo.getInstallSnapshotState();
 779             if (installSnapshotState == null) {
 780                 installSnapshotState = new LeaderInstallSnapshotState(context.getConfigParams().getSnapshotChunkSize(),
 781                         logName());
 782                 followerLogInfo.setLeaderInstallSnapshotState(installSnapshotState);
 783             }
 784
 785             // Ensure the snapshot bytes are set - this is a no-op.
 786             installSnapshotState.setSnapshotBytes(snapshot.get().getSnapshotBytes());
 787
 788             byte[] nextSnapshotChunk = installSnapshotState.getNextChunk();
 789
 790             LOG.debug("{}: next snapshot chunk size for follower {}: {}", logName(), followerLogInfo.getId(),
 791                     nextSnapshotChunk.length);
 792
 793             int nextChunkIndex = installSnapshotState.incrementChunkIndex();
 794             Optional<ServerConfigurationPayload> serverConfig = Optional.absent();
 795             if(installSnapshotState.isLastChunk(nextChunkIndex)) {
 796                 serverConfig = Optional.fromNullable(context.getPeerServerInfo(true));
 797             }
 798
 799             followerActor.tell(
 800                 new InstallSnapshot(currentTerm(), context.getId(),
 801                     snapshot.get().getLastIncludedIndex(),
 802                     snapshot.get().getLastIncludedTerm(),
 803                     nextSnapshotChunk,
 804                     nextChunkIndex,
 805                     installSnapshotState.getTotalChunks(),
 806                     Optional.of(installSnapshotState.getLastChunkHashCode()),
 807                     serverConfig
 808                 ).toSerializable(followerLogInfo.getRaftVersion()),
 809                 actor()
 810             );
 811
 812             if(LOG.isDebugEnabled()) {
 813                 LOG.debug("{}: InstallSnapshot sent to follower {}, Chunk: {}/{}",
 814                         logName(), followerActor.path(), installSnapshotState.getChunkIndex(),
 815                         installSnapshotState.getTotalChunks());
 816             }
 817         }
 818     }
 819
 820     private void sendHeartBeat() {
 821         if (!followerToLog.isEmpty()) {
 822             LOG.trace("{}: Sending heartbeat", logName());
 823             sendAppendEntries(context.getConfigParams().getHeartBeatInterval().toMillis(), true);
 824         }
 825     }
 826
 827     private void stopHeartBeat() {
 828         if (heartbeatSchedule != null && !heartbeatSchedule.isCancelled()) {
 829             heartbeatSchedule.cancel();
 830         }
 831     }
 832
 833     private void scheduleHeartBeat(FiniteDuration interval) {
 834         if (followerToLog.isEmpty()) {
 835             // Optimization - do not bother scheduling a heartbeat as there are
 836             // no followers
 837             return;
 838         }
 839
 840         stopHeartBeat();
 841
 842         // Schedule a heartbeat. When the scheduler triggers a SendHeartbeat
 843         // message is sent to itself.
 844         // Scheduling the heartbeat only once here because heartbeats do not
 845         // need to be sent if there are other messages being sent to the remote
 846         // actor.
 847         heartbeatSchedule = context.getActorSystem().scheduler().scheduleOnce(
 848             interval, context.getActor(), SendHeartBeat.INSTANCE,
 849             context.getActorSystem().dispatcher(), context.getActor());
 850     }
 851
 852     @Override
 853     public void close() {
 854         stopHeartBeat();
 855     }
 856
 857     @Override
 858     public final String getLeaderId() {
 859         return context.getId();
 860     }
 861
 862     @Override
 863     public final short getLeaderPayloadVersion() {
 864         return context.getPayloadVersion();
 865     }
 866
 867     protected boolean isLeaderIsolated() {
 868         int minPresent = getMinIsolatedLeaderPeerCount();
 869         for (FollowerLogInformation followerLogInformation : followerToLog.values()) {
 870             final PeerInfo peerInfo = context.getPeerInfo(followerLogInformation.getId());
 871             if(peerInfo != null && peerInfo.isVoting() && followerLogInformation.isFollowerActive()) {
 872                 --minPresent;
 873                 if (minPresent == 0) {
 874                     return false;
 875                 }
 876             }
 877         }
 878         return minPresent != 0;
 879     }
 880
 881     // called from example-actor for printing the follower-states
 882     public String printFollowerStates() {
 883         final StringBuilder sb = new StringBuilder();
 884
 885         sb.append('[');
 886         for (FollowerLogInformation followerLogInformation : followerToLog.values()) {
 887             sb.append('{');
 888             sb.append(followerLogInformation.getId());
 889             sb.append(" state:");
 890             sb.append(followerLogInformation.isFollowerActive());
 891             sb.append("},");
 892         }
 893         sb.append(']');
 894
 895         return sb.toString();
 896     }
 897
 898     @VisibleForTesting
 899     public FollowerLogInformation getFollower(String followerId) {
 900         return followerToLog.get(followerId);
 901     }
 902
 903     @VisibleForTesting
 904     public int followerLogSize() {
 905         return followerToLog.size();
 906     }
 907
 908     private static class SnapshotHolder {
 909         private final long lastIncludedTerm;
 910         private final long lastIncludedIndex;
 911         private final ByteString snapshotBytes;
 912
 913         SnapshotHolder(Snapshot snapshot) {
 914             this.lastIncludedTerm = snapshot.getLastAppliedTerm();
 915             this.lastIncludedIndex = snapshot.getLastAppliedIndex();
 916             this.snapshotBytes = ByteString.copyFrom(snapshot.getState());
 917         }
 918
 919         long getLastIncludedTerm() {
 920             return lastIncludedTerm;
 921         }
 922
 923         long getLastIncludedIndex() {
 924             return lastIncludedIndex;
 925         }
 926
 927         ByteString getSnapshotBytes() {
 928             return snapshotBytes;
 929         }
 930     }
 931 }