opendaylight/md-sal/sal-akka-raft/src/main/java/org/opendaylight/controller/cluster/raft/behaviors/AbstractLeader.java

   1 /*
   2  * Copyright (c) 2014 Cisco Systems, Inc. and others.  All rights reserved.
   3  *
   4  * This program and the accompanying materials are made available under the
   5  * terms of the Eclipse Public License v1.0 which accompanies this distribution,
   6  * and is available at http://www.eclipse.org/legal/epl-v10.html
   7  */
   8
   9 package org.opendaylight.controller.cluster.raft.behaviors;
  10
  11 import akka.actor.ActorRef;
  12 import akka.actor.ActorSelection;
  13 import akka.actor.Cancellable;
  14 import com.google.common.annotations.VisibleForTesting;
  15 import com.google.common.base.Optional;
  16 import com.google.common.base.Preconditions;
  17 import com.google.common.base.Throwables;
  18 import com.google.common.io.ByteSource;
  19 import java.io.IOException;
  20 import java.util.Collection;
  21 import java.util.Collections;
  22 import java.util.HashMap;
  23 import java.util.Iterator;
  24 import java.util.LinkedList;
  25 import java.util.List;
  26 import java.util.Map;
  27 import java.util.Map.Entry;
  28 import java.util.Queue;
  29 import javax.annotation.Nullable;
  30 import org.opendaylight.controller.cluster.raft.ClientRequestTracker;
  31 import org.opendaylight.controller.cluster.raft.ClientRequestTrackerImpl;
  32 import org.opendaylight.controller.cluster.raft.FollowerLogInformation;
  33 import org.opendaylight.controller.cluster.raft.FollowerLogInformationImpl;
  34 import org.opendaylight.controller.cluster.raft.PeerInfo;
  35 import org.opendaylight.controller.cluster.raft.RaftActorContext;
  36 import org.opendaylight.controller.cluster.raft.RaftState;
  37 import org.opendaylight.controller.cluster.raft.ReplicatedLogEntry;
  38 import org.opendaylight.controller.cluster.raft.VotingState;
  39 import org.opendaylight.controller.cluster.raft.base.messages.CheckConsensusReached;
  40 import org.opendaylight.controller.cluster.raft.base.messages.Replicate;
  41 import org.opendaylight.controller.cluster.raft.base.messages.SendHeartBeat;
  42 import org.opendaylight.controller.cluster.raft.base.messages.SendInstallSnapshot;
  43 import org.opendaylight.controller.cluster.raft.messages.AppendEntries;
  44 import org.opendaylight.controller.cluster.raft.messages.AppendEntriesReply;
  45 import org.opendaylight.controller.cluster.raft.messages.InstallSnapshot;
  46 import org.opendaylight.controller.cluster.raft.messages.InstallSnapshotReply;
  47 import org.opendaylight.controller.cluster.raft.messages.RaftRPC;
  48 import org.opendaylight.controller.cluster.raft.messages.RequestVoteReply;
  49 import org.opendaylight.controller.cluster.raft.messages.UnInitializedFollowerSnapshotReply;
  50 import org.opendaylight.controller.cluster.raft.persisted.ServerConfigurationPayload;
  51 import org.opendaylight.controller.cluster.raft.persisted.Snapshot;
  52 import scala.concurrent.duration.FiniteDuration;
  53
  54 /**
  55  * The behavior of a RaftActor when it is in the Leader state
  56  *
  57  * <p>
  58  * Leaders:
  59  * <ul>
  60  * <li> Upon election: send initial empty AppendEntries RPCs
  61  * (heartbeat) to each server; repeat during idle periods to
  62  * prevent election timeouts (§5.2)
  63  * <li> If command received from client: append entry to local log,
  64  * respond after entry applied to state machine (§5.3)
  65  * <li> If last log index ≥ nextIndex for a follower: send
  66  * AppendEntries RPC with log entries starting at nextIndex
  67  * <li> If successful: update nextIndex and matchIndex for
  68  * follower (§5.3)
  69  * <li> If AppendEntries fails because of log inconsistency:
  70  * decrement nextIndex and retry (§5.3)
  71  * <li> If there exists an N such that N &gt; commitIndex, a majority
  72  * of matchIndex[i] ≥ N, and log[N].term == currentTerm:
  73  * set commitIndex = N (§5.3, §5.4).
  74  * </ul>
  75  */
  76 public abstract class AbstractLeader extends AbstractRaftActorBehavior {
  77     private final Map<String, FollowerLogInformation> followerToLog = new HashMap<>();
  78
  79     /**
  80      * Lookup table for request contexts based on journal index. We could use a {@link Map} here, but we really
  81      * expect the entries to be modified in sequence, hence we open-code the lookup.
  82      * TODO: Evaluate the use of ArrayDeque(), as that has lower memory overhead. Non-head removals are more costly,
  83      *       but we already expect those to be far from frequent.
  84      */
  85     private final Queue<ClientRequestTracker> trackers = new LinkedList<>();
  86
  87     private Cancellable heartbeatSchedule = null;
  88     private Optional<SnapshotHolder> snapshotHolder = Optional.absent();
  89     private int minReplicationCount;
  90
  91     protected AbstractLeader(RaftActorContext context, RaftState state,
  92             @Nullable AbstractLeader initializeFromLeader) {
  93         super(context, state);
  94
  95         if (initializeFromLeader != null) {
  96             followerToLog.putAll(initializeFromLeader.followerToLog);
  97             snapshotHolder = initializeFromLeader.snapshotHolder;
  98             trackers.addAll(initializeFromLeader.trackers);
  99         } else {
 100             for (PeerInfo peerInfo: context.getPeers()) {
 101                 FollowerLogInformation followerLogInformation = new FollowerLogInformationImpl(peerInfo, -1, context);
 102                 followerToLog.put(peerInfo.getId(), followerLogInformation);
 103             }
 104         }
 105
 106         log.debug("{}: Election: Leader has following peers: {}", logName(), getFollowerIds());
 107
 108         updateMinReplicaCount();
 109
 110         // Immediately schedule a heartbeat
 111         // Upon election: send initial empty AppendEntries RPCs
 112         // (heartbeat) to each server; repeat during idle periods to
 113         // prevent election timeouts (§5.2)
 114         sendAppendEntries(0, false);
 115
 116         // It is important to schedule this heartbeat here
 117         scheduleHeartBeat(context.getConfigParams().getHeartBeatInterval());
 118     }
 119
 120     protected AbstractLeader(RaftActorContext context, RaftState state) {
 121         this(context, state, null);
 122     }
 123
 124     /**
 125      * Return an immutable collection of follower identifiers.
 126      *
 127      * @return Collection of follower IDs
 128      */
 129     public final Collection<String> getFollowerIds() {
 130         return followerToLog.keySet();
 131     }
 132
 133     public void addFollower(String followerId) {
 134         FollowerLogInformation followerLogInformation = new FollowerLogInformationImpl(
 135                 context.getPeerInfo(followerId), -1, context);
 136         followerToLog.put(followerId, followerLogInformation);
 137
 138         if (heartbeatSchedule == null) {
 139             scheduleHeartBeat(context.getConfigParams().getHeartBeatInterval());
 140         }
 141     }
 142
 143     public void removeFollower(String followerId) {
 144         followerToLog.remove(followerId);
 145     }
 146
 147     public void updateMinReplicaCount() {
 148         int numVoting = 0;
 149         for (PeerInfo peer: context.getPeers()) {
 150             if (peer.isVoting()) {
 151                 numVoting++;
 152             }
 153         }
 154
 155         minReplicationCount = getMajorityVoteCount(numVoting);
 156     }
 157
 158     protected int getMinIsolatedLeaderPeerCount() {
 159       //the isolated Leader peer count will be 1 less than the majority vote count.
 160         //this is because the vote count has the self vote counted in it
 161         //for e.g
 162         //0 peers = 1 votesRequired , minIsolatedLeaderPeerCount = 0
 163         //2 peers = 2 votesRequired , minIsolatedLeaderPeerCount = 1
 164         //4 peers = 3 votesRequired, minIsolatedLeaderPeerCount = 2
 165
 166         return minReplicationCount > 0 ? minReplicationCount - 1 : 0;
 167     }
 168
 169     @VisibleForTesting
 170     void setSnapshot(@Nullable SnapshotHolder snapshotHolder) {
 171         this.snapshotHolder = Optional.fromNullable(snapshotHolder);
 172     }
 173
 174     @VisibleForTesting
 175     boolean hasSnapshot() {
 176         return snapshotHolder.isPresent();
 177     }
 178
 179     @Override
 180     protected RaftActorBehavior handleAppendEntries(ActorRef sender,
 181         AppendEntries appendEntries) {
 182
 183         log.debug("{}: handleAppendEntries: {}", logName(), appendEntries);
 184
 185         return this;
 186     }
 187
 188     @Override
 189     protected RaftActorBehavior handleAppendEntriesReply(ActorRef sender, AppendEntriesReply appendEntriesReply) {
 190         log.trace("{}: handleAppendEntriesReply: {}", logName(), appendEntriesReply);
 191
 192         // Update the FollowerLogInformation
 193         String followerId = appendEntriesReply.getFollowerId();
 194         FollowerLogInformation followerLogInformation = followerToLog.get(followerId);
 195
 196         if (followerLogInformation == null) {
 197             log.error("{}: handleAppendEntriesReply - unknown follower {}", logName(), followerId);
 198             return this;
 199         }
 200
 201         if (followerLogInformation.timeSinceLastActivity()
 202                 > context.getConfigParams().getElectionTimeOutInterval().toMillis()) {
 203             log.warn("{} : handleAppendEntriesReply delayed beyond election timeout, "
 204                     + "appendEntriesReply : {}, timeSinceLastActivity : {}, lastApplied : {}, commitIndex : {}",
 205                     logName(), appendEntriesReply, followerLogInformation.timeSinceLastActivity(),
 206                     context.getLastApplied(), context.getCommitIndex());
 207         }
 208
 209         followerLogInformation.markFollowerActive();
 210         followerLogInformation.setPayloadVersion(appendEntriesReply.getPayloadVersion());
 211         followerLogInformation.setRaftVersion(appendEntriesReply.getRaftVersion());
 212
 213         long followerLastLogIndex = appendEntriesReply.getLogLastIndex();
 214         long followersLastLogTermInLeadersLog = getLogEntryTerm(followerLastLogIndex);
 215         boolean updated = false;
 216         if (appendEntriesReply.getLogLastIndex() > context.getReplicatedLog().lastIndex()) {
 217             // The follower's log is actually ahead of the leader's log. Normally this doesn't happen
 218             // in raft as a node cannot become leader if it's log is behind another's. However, the
 219             // non-voting semantics deviate a bit from raft. Only voting members participate in
 220             // elections and can become leader so it's possible for a non-voting follower to be ahead
 221             // of the leader. This can happen if persistence is disabled and all voting members are
 222             // restarted. In this case, the voting leader will start out with an empty log however
 223             // the non-voting followers still retain the previous data in memory. On the first
 224             // AppendEntries, the non-voting follower returns a successful reply b/c the prevLogIndex
 225             // sent by the leader is -1 and thus the integrity checks pass. However the follower's returned
 226             // lastLogIndex may be higher in which case we want to reset the follower by installing a
 227             // snapshot. It's also possible that the follower's last log index is behind the leader's.
 228             // However in this case the log terms won't match and the logs will conflict - this is handled
 229             // elsewhere.
 230             log.debug("{}: handleAppendEntriesReply: follower {} lastIndex {} is ahead of our lastIndex {} - "
 231                     + "forcing install snaphot", logName(), followerLogInformation.getId(),
 232                     appendEntriesReply.getLogLastIndex(), context.getReplicatedLog().lastIndex());
 233
 234             followerLogInformation.setMatchIndex(-1);
 235             followerLogInformation.setNextIndex(-1);
 236
 237             initiateCaptureSnapshot(followerId);
 238
 239             updated = true;
 240         } else if (appendEntriesReply.isSuccess()) {
 241             if (followerLastLogIndex >= 0 && followersLastLogTermInLeadersLog >= 0
 242                     && followersLastLogTermInLeadersLog != appendEntriesReply.getLogLastTerm()) {
 243                 // The follower's last entry is present in the leader's journal but the terms don't match so the
 244                 // follower has a conflicting entry. Since the follower didn't report that it's out of sync, this means
 245                 // either the previous leader entry sent didn't conflict or the previous leader entry is in the snapshot
 246                 // and no longer in the journal. Either way, we set the follower's next index to 1 less than the last
 247                 // index reported by the follower. For the former case, the leader will send all entries starting with
 248                 // the previous follower's index and the follower will remove and replace the conflicting entries as
 249                 // needed. For the latter, the leader will initiate an install snapshot.
 250
 251                 followerLogInformation.setNextIndex(followerLastLogIndex - 1);
 252                 updated = true;
 253
 254                 log.debug("{}: handleAppendEntriesReply: follower {} last log term {} for index {} conflicts with the "
 255                         + "leader's {} - set the follower's next index to {}", logName(),
 256                         followerId, appendEntriesReply.getLogLastTerm(), appendEntriesReply.getLogLastIndex(),
 257                         followersLastLogTermInLeadersLog, followerLogInformation.getNextIndex());
 258             } else {
 259                 updated = updateFollowerLogInformation(followerLogInformation, appendEntriesReply);
 260             }
 261         } else {
 262             log.debug("{}: handleAppendEntriesReply: received unsuccessful reply: {}", logName(), appendEntriesReply);
 263
 264             if (appendEntriesReply.isForceInstallSnapshot()) {
 265                 // Reset the followers match and next index. This is to signal that this follower has nothing
 266                 // in common with this Leader and so would require a snapshot to be installed
 267                 followerLogInformation.setMatchIndex(-1);
 268                 followerLogInformation.setNextIndex(-1);
 269
 270                 // Force initiate a snapshot capture
 271                 initiateCaptureSnapshot(followerId);
 272             } else if (followerLastLogIndex < 0 || followersLastLogTermInLeadersLog >= 0
 273                     && followersLastLogTermInLeadersLog == appendEntriesReply.getLogLastTerm()) {
 274                 // The follower's log is empty or the last entry is present in the leader's journal
 275                 // and the terms match so the follower is just behind the leader's journal from
 276                 // the last snapshot, if any. We'll catch up the follower quickly by starting at the
 277                 // follower's last log index.
 278
 279                 updated = updateFollowerLogInformation(followerLogInformation, appendEntriesReply);
 280             } else {
 281                 // The follower's log conflicts with leader's log so decrement follower's next index by 1
 282                 // in an attempt to find where the logs match.
 283
 284                 followerLogInformation.decrNextIndex();
 285                 updated = true;
 286
 287                 log.debug("{}: follower's last log term {} conflicts with the leader's {} - dec next index to {}",
 288                         logName(), appendEntriesReply.getLogLastTerm(), followersLastLogTermInLeadersLog,
 289                         followerLogInformation.getNextIndex());
 290             }
 291         }
 292
 293         if (log.isTraceEnabled()) {
 294             log.trace("{}: handleAppendEntriesReply from {}: commitIndex: {}, lastAppliedIndex: {}, currentTerm: {}",
 295                     logName(), followerId, context.getCommitIndex(), context.getLastApplied(), currentTerm());
 296         }
 297
 298         possiblyUpdateCommitIndex();
 299
 300         //Send the next log entry immediately, if possible, no need to wait for heartbeat to trigger that event
 301         sendUpdatesToFollower(followerId, followerLogInformation, false, !updated);
 302
 303         return this;
 304     }
 305
 306     private void possiblyUpdateCommitIndex() {
 307         // Figure out if we can update the the commitIndex as follows:
 308         //   If there exists an index N such that N > commitIndex, a majority of matchIndex[i] ≥ N,
 309         //     and log[N].term == currentTerm:
 310         //   set commitIndex = N (§5.3, §5.4).
 311         for (long index = context.getCommitIndex() + 1; ; index++) {
 312             ReplicatedLogEntry replicatedLogEntry = context.getReplicatedLog().get(index);
 313             if (replicatedLogEntry == null) {
 314                 log.trace("{}: ReplicatedLogEntry not found for index {} - snapshotIndex: {}, journal size: {}",
 315                         logName(), index, context.getReplicatedLog().getSnapshotIndex(),
 316                         context.getReplicatedLog().size());
 317                 break;
 318             }
 319
 320             // Count our entry if it has been persisted.
 321             int replicatedCount = replicatedLogEntry.isPersistencePending() ? 0 : 1;
 322
 323             if (replicatedCount == 0) {
 324                 // We don't commit and apply a log entry until we've gotten the ack from our local persistence,
 325                 // even though there *shouldn't* be any issue with updating the commit index if we get a consensus
 326                 // amongst the followers w/o the local persistence ack.
 327                 break;
 328             }
 329
 330             log.trace("{}: checking Nth index {}", logName(), index);
 331             for (FollowerLogInformation info : followerToLog.values()) {
 332                 final PeerInfo peerInfo = context.getPeerInfo(info.getId());
 333                 if (info.getMatchIndex() >= index && peerInfo != null && peerInfo.isVoting()) {
 334                     replicatedCount++;
 335                 } else if (log.isTraceEnabled()) {
 336                     log.trace("{}: Not counting follower {} - matchIndex: {}, {}", logName(), info.getId(),
 337                             info.getMatchIndex(), peerInfo);
 338                 }
 339             }
 340
 341             if (log.isTraceEnabled()) {
 342                 log.trace("{}: replicatedCount {}, minReplicationCount: {}", logName(), replicatedCount,
 343                         minReplicationCount);
 344             }
 345
 346             if (replicatedCount >= minReplicationCount) {
 347                 // Don't update the commit index if the log entry is from a previous term, as per §5.4.1:
 348                 // "Raft never commits log entries from previous terms by counting replicas".
 349                 // However we keep looping so we can make progress when new entries in the current term
 350                 // reach consensus, as per §5.4.1: "once an entry from the current term is committed by
 351                 // counting replicas, then all prior entries are committed indirectly".
 352                 if (replicatedLogEntry.getTerm() == currentTerm()) {
 353                     log.trace("{}: Setting commit index to {}", logName(), index);
 354                     context.setCommitIndex(index);
 355                 } else {
 356                     log.debug("{}: Not updating commit index to {} - retrieved log entry with index {}, "
 357                             + "term {} does not match the current term {}", logName(), index,
 358                             replicatedLogEntry.getIndex(), replicatedLogEntry.getTerm(), currentTerm());
 359                 }
 360             } else {
 361                 log.trace("{}: minReplicationCount not reached, actual {} - breaking", logName(), replicatedCount);
 362                 break;
 363             }
 364         }
 365
 366         // Apply the change to the state machine
 367         if (context.getCommitIndex() > context.getLastApplied()) {
 368             log.debug("{}: Applying to log - commitIndex: {}, lastAppliedIndex: {}", logName(),
 369                     context.getCommitIndex(), context.getLastApplied());
 370
 371             applyLogToStateMachine(context.getCommitIndex());
 372         }
 373
 374         if (!context.getSnapshotManager().isCapturing()) {
 375             purgeInMemoryLog();
 376         }
 377     }
 378
 379     private boolean updateFollowerLogInformation(FollowerLogInformation followerLogInformation,
 380             AppendEntriesReply appendEntriesReply) {
 381         boolean updated = followerLogInformation.setMatchIndex(appendEntriesReply.getLogLastIndex());
 382         updated = followerLogInformation.setNextIndex(appendEntriesReply.getLogLastIndex() + 1) || updated;
 383
 384         if (updated && log.isDebugEnabled()) {
 385             log.debug(
 386                 "{}: handleAppendEntriesReply - FollowerLogInformation for {} updated: matchIndex: {}, nextIndex: {}",
 387                 logName(), followerLogInformation.getId(), followerLogInformation.getMatchIndex(),
 388                 followerLogInformation.getNextIndex());
 389         }
 390         return updated;
 391     }
 392
 393     private void purgeInMemoryLog() {
 394         //find the lowest index across followers which has been replicated to all.
 395         // lastApplied if there are no followers, so that we keep clearing the log for single-node
 396         // we would delete the in-mem log from that index on, in-order to minimize mem usage
 397         // we would also share this info thru AE with the followers so that they can delete their log entries as well.
 398         long minReplicatedToAllIndex = followerToLog.isEmpty() ? context.getLastApplied() : Long.MAX_VALUE;
 399         for (FollowerLogInformation info : followerToLog.values()) {
 400             minReplicatedToAllIndex = Math.min(minReplicatedToAllIndex, info.getMatchIndex());
 401         }
 402
 403         super.performSnapshotWithoutCapture(minReplicatedToAllIndex);
 404     }
 405
 406     @Override
 407     protected ClientRequestTracker removeClientRequestTracker(long logIndex) {
 408         final Iterator<ClientRequestTracker> it = trackers.iterator();
 409         while (it.hasNext()) {
 410             final ClientRequestTracker t = it.next();
 411             if (t.getIndex() == logIndex) {
 412                 it.remove();
 413                 return t;
 414             }
 415         }
 416
 417         return null;
 418     }
 419
 420     @Override
 421     protected RaftActorBehavior handleRequestVoteReply(ActorRef sender,
 422         RequestVoteReply requestVoteReply) {
 423         return this;
 424     }
 425
 426     protected void beforeSendHeartbeat(){}
 427
 428     @Override
 429     public RaftActorBehavior handleMessage(ActorRef sender, Object message) {
 430         Preconditions.checkNotNull(sender, "sender should not be null");
 431
 432         if (message instanceof RaftRPC) {
 433             RaftRPC rpc = (RaftRPC) message;
 434             // If RPC request or response contains term T > currentTerm:
 435             // set currentTerm = T, convert to follower (§5.1)
 436             // This applies to all RPC messages and responses
 437             if (rpc.getTerm() > context.getTermInformation().getCurrentTerm()) {
 438                 log.debug("{}: Term {} in \"{}\" message is greater than leader's term {} - switching to Follower",
 439                         logName(), rpc.getTerm(), rpc, context.getTermInformation().getCurrentTerm());
 440
 441                 context.getTermInformation().updateAndPersist(rpc.getTerm(), null);
 442
 443                 return internalSwitchBehavior(RaftState.Follower);
 444             }
 445         }
 446
 447         if (message instanceof SendHeartBeat) {
 448             beforeSendHeartbeat();
 449             sendHeartBeat();
 450             scheduleHeartBeat(context.getConfigParams().getHeartBeatInterval());
 451         } else if (message instanceof SendInstallSnapshot) {
 452             SendInstallSnapshot sendInstallSnapshot = (SendInstallSnapshot) message;
 453             setSnapshot(new SnapshotHolder(sendInstallSnapshot.getSnapshot(), sendInstallSnapshot.getSnapshotBytes()));
 454             sendInstallSnapshot();
 455         } else if (message instanceof Replicate) {
 456             replicate((Replicate) message);
 457         } else if (message instanceof InstallSnapshotReply) {
 458             handleInstallSnapshotReply((InstallSnapshotReply) message);
 459         } else if (message instanceof CheckConsensusReached) {
 460             possiblyUpdateCommitIndex();
 461         } else {
 462             return super.handleMessage(sender, message);
 463         }
 464
 465         return this;
 466     }
 467
 468     private void handleInstallSnapshotReply(InstallSnapshotReply reply) {
 469         log.debug("{}: handleInstallSnapshotReply: {}", logName(), reply);
 470
 471         String followerId = reply.getFollowerId();
 472         FollowerLogInformation followerLogInformation = followerToLog.get(followerId);
 473         if (followerLogInformation == null) {
 474             // This can happen during AddServer if it times out.
 475             log.error("{}: FollowerLogInformation not found for follower {} in InstallSnapshotReply",
 476                     logName(), followerId);
 477             return;
 478         }
 479
 480         LeaderInstallSnapshotState installSnapshotState = followerLogInformation.getInstallSnapshotState();
 481         if (installSnapshotState == null) {
 482             log.error("{}: LeaderInstallSnapshotState not found for follower {} in InstallSnapshotReply",
 483                     logName(), followerId);
 484             return;
 485         }
 486
 487         followerLogInformation.markFollowerActive();
 488
 489         if (installSnapshotState.getChunkIndex() == reply.getChunkIndex()) {
 490             boolean wasLastChunk = false;
 491             if (reply.isSuccess()) {
 492                 if (installSnapshotState.isLastChunk(reply.getChunkIndex())) {
 493                     //this was the last chunk reply
 494                     log.debug("{}: InstallSnapshotReply received, last chunk received, Chunk: {}. Follower: {} -"
 495                             + " Setting nextIndex: {}", logName(), reply.getChunkIndex(), followerId,
 496                             context.getReplicatedLog().getSnapshotIndex() + 1);
 497
 498                     long followerMatchIndex = snapshotHolder.get().getLastIncludedIndex();
 499                     followerLogInformation.setMatchIndex(followerMatchIndex);
 500                     followerLogInformation.setNextIndex(followerMatchIndex + 1);
 501                     followerLogInformation.clearLeaderInstallSnapshotState();
 502
 503                     log.debug("{}: follower: {}, matchIndex set to {}, nextIndex set to {}",
 504                         logName(), followerId, followerLogInformation.getMatchIndex(),
 505                         followerLogInformation.getNextIndex());
 506
 507                     if (!anyFollowersInstallingSnapshot()) {
 508                         // once there are no pending followers receiving snapshots
 509                         // we can remove snapshot from the memory
 510                         setSnapshot(null);
 511                     }
 512
 513                     wasLastChunk = true;
 514                     if (context.getPeerInfo(followerId).getVotingState() == VotingState.VOTING_NOT_INITIALIZED) {
 515                         UnInitializedFollowerSnapshotReply unInitFollowerSnapshotSuccess =
 516                                              new UnInitializedFollowerSnapshotReply(followerId);
 517                         context.getActor().tell(unInitFollowerSnapshotSuccess, context.getActor());
 518                         log.debug("Sent message UnInitializedFollowerSnapshotReply to self");
 519                     }
 520                 } else {
 521                     installSnapshotState.markSendStatus(true);
 522                 }
 523             } else {
 524                 log.info("{}: InstallSnapshotReply received sending snapshot chunk failed, Will retry, Chunk: {}",
 525                         logName(), reply.getChunkIndex());
 526
 527                 installSnapshotState.markSendStatus(false);
 528             }
 529
 530             if (wasLastChunk && !context.getSnapshotManager().isCapturing()) {
 531                 // Since the follower is now caught up try to purge the log.
 532                 purgeInMemoryLog();
 533             } else if (!wasLastChunk && installSnapshotState.canSendNextChunk()) {
 534                 ActorSelection followerActor = context.getPeerActorSelection(followerId);
 535                 if (followerActor != null) {
 536                     sendSnapshotChunk(followerActor, followerLogInformation);
 537                 }
 538             }
 539
 540         } else {
 541             log.error("{}: Chunk index {} in InstallSnapshotReply from follower {} does not match expected index {}",
 542                     logName(), reply.getChunkIndex(), followerId,
 543                     installSnapshotState.getChunkIndex());
 544
 545             if (reply.getChunkIndex() == LeaderInstallSnapshotState.INVALID_CHUNK_INDEX) {
 546                 // Since the Follower did not find this index to be valid we should reset the follower snapshot
 547                 // so that Installing the snapshot can resume from the beginning
 548                 installSnapshotState.reset();
 549             }
 550         }
 551     }
 552
 553     private boolean anyFollowersInstallingSnapshot() {
 554         for (FollowerLogInformation info: followerToLog.values()) {
 555             if (info.getInstallSnapshotState() != null) {
 556                 return true;
 557             }
 558
 559         }
 560
 561         return false;
 562     }
 563
 564     private void replicate(Replicate replicate) {
 565         long logIndex = replicate.getReplicatedLogEntry().getIndex();
 566
 567         log.debug("{}: Replicate message: identifier: {}, logIndex: {}, payload: {}, isSendImmediate: {}", logName(),
 568                 replicate.getIdentifier(), logIndex, replicate.getReplicatedLogEntry().getData().getClass(),
 569                 replicate.isSendImmediate());
 570
 571         // Create a tracker entry we will use this later to notify the
 572         // client actor
 573         if (replicate.getClientActor() != null) {
 574             trackers.add(new ClientRequestTrackerImpl(replicate.getClientActor(), replicate.getIdentifier(),
 575                     logIndex));
 576         }
 577
 578         boolean applyModificationToState = !context.anyVotingPeers()
 579                 || context.getRaftPolicy().applyModificationToStateBeforeConsensus();
 580
 581         if (applyModificationToState) {
 582             context.setCommitIndex(logIndex);
 583             applyLogToStateMachine(logIndex);
 584         }
 585
 586         if (replicate.isSendImmediate() && !followerToLog.isEmpty()) {
 587             sendAppendEntries(0, false);
 588         }
 589     }
 590
 591     protected void sendAppendEntries(long timeSinceLastActivityInterval, boolean isHeartbeat) {
 592         // Send an AppendEntries to all followers
 593         for (Entry<String, FollowerLogInformation> e : followerToLog.entrySet()) {
 594             final String followerId = e.getKey();
 595             final FollowerLogInformation followerLogInformation = e.getValue();
 596             // This checks helps not to send a repeat message to the follower
 597             if (!followerLogInformation.isFollowerActive()
 598                     || followerLogInformation.timeSinceLastActivity() >= timeSinceLastActivityInterval) {
 599                 sendUpdatesToFollower(followerId, followerLogInformation, true, isHeartbeat);
 600             }
 601         }
 602     }
 603
 604     /**
 605      * This method checks if any update needs to be sent to the given follower. This includes append log entries,
 606      * sending next snapshot chunk, and initiating a snapshot.
 607      */
 608     private void sendUpdatesToFollower(String followerId, FollowerLogInformation followerLogInformation,
 609                                        boolean sendHeartbeat, boolean isHeartbeat) {
 610
 611         ActorSelection followerActor = context.getPeerActorSelection(followerId);
 612         if (followerActor != null) {
 613             long followerNextIndex = followerLogInformation.getNextIndex();
 614             boolean isFollowerActive = followerLogInformation.isFollowerActive();
 615             boolean sendAppendEntries = false;
 616             List<ReplicatedLogEntry> entries = Collections.emptyList();
 617
 618             LeaderInstallSnapshotState installSnapshotState = followerLogInformation.getInstallSnapshotState();
 619             if (installSnapshotState != null) {
 620                 // if install snapshot is in process , then sent next chunk if possible
 621                 if (isFollowerActive && installSnapshotState.canSendNextChunk()) {
 622                     sendSnapshotChunk(followerActor, followerLogInformation);
 623                 } else if (sendHeartbeat) {
 624                     // we send a heartbeat even if we have not received a reply for the last chunk
 625                     sendAppendEntries = true;
 626                 }
 627             } else {
 628                 long leaderLastIndex = context.getReplicatedLog().lastIndex();
 629                 long leaderSnapShotIndex = context.getReplicatedLog().getSnapshotIndex();
 630
 631                 if (!isHeartbeat && log.isDebugEnabled() || log.isTraceEnabled()) {
 632                     log.debug("{}: Checking sendAppendEntries for follower {}: active: {}, followerNextIndex: {}, "
 633                             + "leaderLastIndex: {}, leaderSnapShotIndex: {}", logName(), followerId, isFollowerActive,
 634                             followerNextIndex, leaderLastIndex, leaderSnapShotIndex);
 635                 }
 636
 637                 if (isFollowerActive && context.getReplicatedLog().isPresent(followerNextIndex)) {
 638
 639                     log.debug("{}: sendAppendEntries: {} is present for follower {}", logName(),
 640                             followerNextIndex, followerId);
 641
 642                     if (followerLogInformation.okToReplicate()) {
 643                         // Try to send all the entries in the journal but not exceeding the max data size
 644                         // for a single AppendEntries message.
 645                         int maxEntries = (int) context.getReplicatedLog().size();
 646                         entries = context.getReplicatedLog().getFrom(followerNextIndex, maxEntries,
 647                                 context.getConfigParams().getSnapshotChunkSize());
 648                         sendAppendEntries = true;
 649                     }
 650                 } else if (isFollowerActive && followerNextIndex >= 0
 651                         && leaderLastIndex > followerNextIndex && !context.getSnapshotManager().isCapturing()) {
 652                     // if the followers next index is not present in the leaders log, and
 653                     // if the follower is just not starting and if leader's index is more than followers index
 654                     // then snapshot should be sent
 655
 656                     if (log.isDebugEnabled()) {
 657                         log.debug(String.format("%s: InitiateInstallSnapshot to follower: %s, "
 658                                     + "follower-nextIndex: %d, leader-snapshot-index: %d,  "
 659                                     + "leader-last-index: %d", logName(), followerId,
 660                                     followerNextIndex, leaderSnapShotIndex, leaderLastIndex));
 661                     }
 662
 663                     // Send heartbeat to follower whenever install snapshot is initiated.
 664                     sendAppendEntries = true;
 665                     if (canInstallSnapshot(followerNextIndex)) {
 666                         initiateCaptureSnapshot(followerId);
 667                     }
 668
 669                 } else if (sendHeartbeat) {
 670                     // we send an AppendEntries, even if the follower is inactive
 671                     // in-order to update the followers timestamp, in case it becomes active again
 672                     sendAppendEntries = true;
 673                 }
 674
 675             }
 676
 677             if (sendAppendEntries) {
 678                 sendAppendEntriesToFollower(followerActor, entries, followerLogInformation);
 679             }
 680         }
 681     }
 682
 683     private void sendAppendEntriesToFollower(ActorSelection followerActor, List<ReplicatedLogEntry> entries,
 684             FollowerLogInformation followerLogInformation) {
 685         // In certain cases outlined below we don't want to send the actual commit index to prevent the follower from
 686         // possibly committing and applying conflicting entries (those with same index, different term) from a prior
 687         // term that weren't replicated to a majority, which would be a violation of raft.
 688         //     - if the follower isn't active. In this case we don't know the state of the follower and we send an
 689         //       empty AppendEntries as a heart beat to prevent election.
 690         //     - if we're in the process of installing a snapshot. In this case we don't send any new entries but still
 691         //       need to send AppendEntries to prevent election.
 692         boolean isInstallingSnaphot = followerLogInformation.getInstallSnapshotState() != null;
 693         long leaderCommitIndex = isInstallingSnaphot || !followerLogInformation.isFollowerActive() ? -1 :
 694             context.getCommitIndex();
 695
 696         long followerNextIndex = followerLogInformation.getNextIndex();
 697         AppendEntries appendEntries = new AppendEntries(currentTerm(), context.getId(),
 698             getLogEntryIndex(followerNextIndex - 1),
 699             getLogEntryTerm(followerNextIndex - 1), entries,
 700             leaderCommitIndex, super.getReplicatedToAllIndex(), context.getPayloadVersion());
 701
 702         if (!entries.isEmpty() || log.isTraceEnabled()) {
 703             log.debug("{}: Sending AppendEntries to follower {}: {}", logName(), followerLogInformation.getId(),
 704                     appendEntries);
 705         }
 706
 707         followerActor.tell(appendEntries, actor());
 708     }
 709
 710     /**
 711      * Initiates a snapshot capture to install on a follower.
 712      *
 713      * <p>
 714      * Install Snapshot works as follows
 715      *   1. Leader initiates the capture snapshot by calling createSnapshot on the RaftActor.
 716      *   2. On receipt of the CaptureSnapshotReply message, the RaftActor persists the snapshot and makes a call to
 717      *      the Leader's handleMessage with a SendInstallSnapshot message.
 718      *   3. The Leader obtains and stores the Snapshot from the SendInstallSnapshot message and sends it in chunks to
 719      *      the Follower via InstallSnapshot messages.
 720      *   4. For each chunk, the Follower sends back an InstallSnapshotReply.
 721      *   5. On receipt of the InstallSnapshotReply for the last chunk, the Leader marks the install complete for that
 722      *      follower.
 723      *   6. If another follower requires a snapshot and a snapshot has been collected (via SendInstallSnapshot)
 724      *      then send the existing snapshot in chunks to the follower.
 725      *
 726      * @param followerId the id of the follower.
 727      * @return true if capture was initiated, false otherwise.
 728      */
 729     public boolean initiateCaptureSnapshot(String followerId) {
 730         FollowerLogInformation followerLogInfo = followerToLog.get(followerId);
 731         if (snapshotHolder.isPresent()) {
 732             // If a snapshot is present in the memory, most likely another install is in progress no need to capture
 733             // snapshot. This could happen if another follower needs an install when one is going on.
 734             final ActorSelection followerActor = context.getPeerActorSelection(followerId);
 735
 736             // Note: sendSnapshotChunk will set the LeaderInstallSnapshotState.
 737             sendSnapshotChunk(followerActor, followerLogInfo);
 738             return true;
 739         }
 740
 741         boolean captureInitiated = context.getSnapshotManager().captureToInstall(context.getReplicatedLog().last(),
 742             this.getReplicatedToAllIndex(), followerId);
 743         if (captureInitiated) {
 744             followerLogInfo.setLeaderInstallSnapshotState(new LeaderInstallSnapshotState(
 745                 context.getConfigParams().getSnapshotChunkSize(), logName()));
 746         }
 747
 748         return captureInitiated;
 749     }
 750
 751     private boolean canInstallSnapshot(long nextIndex) {
 752         // If the follower's nextIndex is -1 then we might as well send it a snapshot
 753         // Otherwise send it a snapshot only if the nextIndex is not present in the log but is present
 754         // in the snapshot
 755         return nextIndex == -1 || !context.getReplicatedLog().isPresent(nextIndex)
 756                 && context.getReplicatedLog().isInSnapshot(nextIndex);
 757
 758     }
 759
 760
 761     private void sendInstallSnapshot() {
 762         log.debug("{}: sendInstallSnapshot", logName());
 763         for (Entry<String, FollowerLogInformation> e : followerToLog.entrySet()) {
 764             String followerId = e.getKey();
 765             ActorSelection followerActor = context.getPeerActorSelection(followerId);
 766             FollowerLogInformation followerLogInfo = e.getValue();
 767
 768             if (followerActor != null) {
 769                 long nextIndex = followerLogInfo.getNextIndex();
 770                 if (followerLogInfo.getInstallSnapshotState() != null
 771                         || context.getPeerInfo(followerId).getVotingState() == VotingState.VOTING_NOT_INITIALIZED
 772                         || canInstallSnapshot(nextIndex)) {
 773                     sendSnapshotChunk(followerActor, followerLogInfo);
 774                 }
 775             }
 776         }
 777     }
 778
 779     /**
 780      *  Sends a snapshot chunk to a given follower
 781      *  InstallSnapshot should qualify as a heartbeat too.
 782      */
 783     private void sendSnapshotChunk(ActorSelection followerActor, FollowerLogInformation followerLogInfo) {
 784         if (snapshotHolder.isPresent()) {
 785             LeaderInstallSnapshotState installSnapshotState = followerLogInfo.getInstallSnapshotState();
 786             if (installSnapshotState == null) {
 787                 installSnapshotState = new LeaderInstallSnapshotState(context.getConfigParams().getSnapshotChunkSize(),
 788                         logName());
 789                 followerLogInfo.setLeaderInstallSnapshotState(installSnapshotState);
 790             }
 791
 792             try {
 793                 // Ensure the snapshot bytes are set - this is a no-op.
 794                 installSnapshotState.setSnapshotBytes(snapshotHolder.get().getSnapshotBytes());
 795
 796                 byte[] nextSnapshotChunk = installSnapshotState.getNextChunk();
 797
 798                 log.debug("{}: next snapshot chunk size for follower {}: {}", logName(), followerLogInfo.getId(),
 799                         nextSnapshotChunk.length);
 800
 801                 int nextChunkIndex = installSnapshotState.incrementChunkIndex();
 802                 Optional<ServerConfigurationPayload> serverConfig = Optional.absent();
 803                 if (installSnapshotState.isLastChunk(nextChunkIndex)) {
 804                     serverConfig = Optional.fromNullable(context.getPeerServerInfo(true));
 805                 }
 806
 807                 followerActor.tell(
 808                     new InstallSnapshot(currentTerm(), context.getId(),
 809                         snapshotHolder.get().getLastIncludedIndex(),
 810                         snapshotHolder.get().getLastIncludedTerm(),
 811                         nextSnapshotChunk,
 812                         nextChunkIndex,
 813                         installSnapshotState.getTotalChunks(),
 814                         Optional.of(installSnapshotState.getLastChunkHashCode()),
 815                         serverConfig
 816                     ).toSerializable(followerLogInfo.getRaftVersion()),
 817                     actor()
 818                 );
 819
 820                 log.debug("{}: InstallSnapshot sent to follower {}, Chunk: {}/{}", logName(), followerActor.path(),
 821                         installSnapshotState.getChunkIndex(), installSnapshotState.getTotalChunks());
 822             } catch (IOException e) {
 823                 throw Throwables.propagate(e);
 824             }
 825         }
 826     }
 827
 828     private void sendHeartBeat() {
 829         if (!followerToLog.isEmpty()) {
 830             log.trace("{}: Sending heartbeat", logName());
 831             sendAppendEntries(context.getConfigParams().getHeartBeatInterval().toMillis(), true);
 832         }
 833     }
 834
 835     private void stopHeartBeat() {
 836         if (heartbeatSchedule != null && !heartbeatSchedule.isCancelled()) {
 837             heartbeatSchedule.cancel();
 838         }
 839     }
 840
 841     private void scheduleHeartBeat(FiniteDuration interval) {
 842         if (followerToLog.isEmpty()) {
 843             // Optimization - do not bother scheduling a heartbeat as there are
 844             // no followers
 845             return;
 846         }
 847
 848         stopHeartBeat();
 849
 850         // Schedule a heartbeat. When the scheduler triggers a SendHeartbeat
 851         // message is sent to itself.
 852         // Scheduling the heartbeat only once here because heartbeats do not
 853         // need to be sent if there are other messages being sent to the remote
 854         // actor.
 855         heartbeatSchedule = context.getActorSystem().scheduler().scheduleOnce(
 856             interval, context.getActor(), SendHeartBeat.INSTANCE,
 857             context.getActorSystem().dispatcher(), context.getActor());
 858     }
 859
 860     @Override
 861     public void close() {
 862         stopHeartBeat();
 863     }
 864
 865     @Override
 866     public final String getLeaderId() {
 867         return context.getId();
 868     }
 869
 870     @Override
 871     public final short getLeaderPayloadVersion() {
 872         return context.getPayloadVersion();
 873     }
 874
 875     protected boolean isLeaderIsolated() {
 876         int minPresent = getMinIsolatedLeaderPeerCount();
 877         for (FollowerLogInformation followerLogInformation : followerToLog.values()) {
 878             final PeerInfo peerInfo = context.getPeerInfo(followerLogInformation.getId());
 879             if (peerInfo != null && peerInfo.isVoting() && followerLogInformation.isFollowerActive()) {
 880                 --minPresent;
 881                 if (minPresent == 0) {
 882                     return false;
 883                 }
 884             }
 885         }
 886         return minPresent != 0;
 887     }
 888
 889     // called from example-actor for printing the follower-states
 890     public String printFollowerStates() {
 891         final StringBuilder sb = new StringBuilder();
 892
 893         sb.append('[');
 894         for (FollowerLogInformation followerLogInformation : followerToLog.values()) {
 895             sb.append('{');
 896             sb.append(followerLogInformation.getId());
 897             sb.append(" state:");
 898             sb.append(followerLogInformation.isFollowerActive());
 899             sb.append("},");
 900         }
 901         sb.append(']');
 902
 903         return sb.toString();
 904     }
 905
 906     @VisibleForTesting
 907     public FollowerLogInformation getFollower(String followerId) {
 908         return followerToLog.get(followerId);
 909     }
 910
 911     @VisibleForTesting
 912     public int followerLogSize() {
 913         return followerToLog.size();
 914     }
 915
 916     static class SnapshotHolder {
 917         private final long lastIncludedTerm;
 918         private final long lastIncludedIndex;
 919         private final ByteSource snapshotBytes;
 920
 921         SnapshotHolder(Snapshot snapshot, ByteSource snapshotBytes) {
 922             this.lastIncludedTerm = snapshot.getLastAppliedTerm();
 923             this.lastIncludedIndex = snapshot.getLastAppliedIndex();
 924             this.snapshotBytes = snapshotBytes;
 925         }
 926
 927         long getLastIncludedTerm() {
 928             return lastIncludedTerm;
 929         }
 930
 931         long getLastIncludedIndex() {
 932             return lastIncludedIndex;
 933         }
 934
 935         ByteSource getSnapshotBytes() {
 936             return snapshotBytes;
 937         }
 938     }
 939 }