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

   1 /*
   2  * Copyright (c) 2014 Cisco Systems, Inc. and others.  All rights reserved.
   3  *
   4  * This program and the accompanying materials are made available under the
   5  * terms of the Eclipse Public License v1.0 which accompanies this distribution,
   6  * and is available at http://www.eclipse.org/legal/epl-v10.html
   7  */
   8
   9 package org.opendaylight.controller.cluster.raft.behaviors;
  10
  11 import akka.actor.ActorRef;
  12 import akka.actor.ActorSelection;
  13 import akka.actor.Cancellable;
  14 import com.google.common.annotations.VisibleForTesting;
  15 import com.google.common.base.Optional;
  16 import com.google.common.base.Preconditions;
  17 import com.google.protobuf.ByteString;
  18 import java.io.IOException;
  19 import java.util.Arrays;
  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.Snapshot;
  39 import org.opendaylight.controller.cluster.raft.VotingState;
  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 scala.concurrent.duration.FiniteDuration;
  52
  53 /**
  54  * The behavior of a RaftActor when it is in the Leader state
  55  * <p/>
  56  * Leaders:
  57  * <ul>
  58  * <li> Upon election: send initial empty AppendEntries RPCs
  59  * (heartbeat) to each server; repeat during idle periods to
  60  * prevent election timeouts (§5.2)
  61  * <li> If command received from client: append entry to local log,
  62  * respond after entry applied to state machine (§5.3)
  63  * <li> If last log index ≥ nextIndex for a follower: send
  64  * AppendEntries RPC with log entries starting at nextIndex
  65  * <ul>
  66  * <li> If successful: update nextIndex and matchIndex for
  67  * follower (§5.3)
  68  * <li> If AppendEntries fails because of log inconsistency:
  69  * decrement nextIndex and retry (§5.3)
  70  * </ul>
  71  * <li> If there exists an N such that N > commitIndex, a majority
  72  * of matchIndex[i] ≥ N, and log[N].term == currentTerm:
  73  * set commitIndex = N (§5.3, §5.4).
  74  */
  75 public abstract class AbstractLeader extends AbstractRaftActorBehavior {
  76
  77     // The index of the first chunk that is sent when installing a snapshot
  78     public static final int FIRST_CHUNK_INDEX = 1;
  79
  80     // The index that the follower should respond with if it needs the install snapshot to be reset
  81     public static final int INVALID_CHUNK_INDEX = -1;
  82
  83     // This would be passed as the hash code of the last chunk when sending the first chunk
  84     public static final int INITIAL_LAST_CHUNK_HASH_CODE = -1;
  85
  86     private final Map<String, FollowerLogInformation> followerToLog = new HashMap<>();
  87     private final Map<String, FollowerToSnapshot> mapFollowerToSnapshot = new HashMap<>();
  88
  89     /**
  90      * Lookup table for request contexts based on journal index. We could use a {@link Map} here, but we really
  91      * expect the entries to be modified in sequence, hence we open-code the lookup.
  92      *
  93      * TODO: Evaluate the use of ArrayDeque(), as that has lower memory overhead. Non-head removals are more costly,
  94      *       but we already expect those to be far from frequent.
  95      */
  96     private final Queue<ClientRequestTracker> trackers = new LinkedList<>();
  97
  98     private Cancellable heartbeatSchedule = null;
  99     private Optional<SnapshotHolder> snapshot;
 100     private int minReplicationCount;
 101
 102     protected AbstractLeader(RaftActorContext context, RaftState state,
 103             @Nullable AbstractLeader initializeFromLeader) {
 104         super(context, state);
 105
 106         if(initializeFromLeader != null) {
 107             followerToLog.putAll(initializeFromLeader.followerToLog);
 108         } else {
 109             for(PeerInfo peerInfo: context.getPeers()) {
 110                 FollowerLogInformation followerLogInformation = new FollowerLogInformationImpl(peerInfo, -1, context);
 111                 followerToLog.put(peerInfo.getId(), followerLogInformation);
 112             }
 113         }
 114
 115         LOG.debug("{}: Election: Leader has following peers: {}", logName(), getFollowerIds());
 116
 117         updateMinReplicaCount();
 118
 119         snapshot = Optional.absent();
 120
 121         // Immediately schedule a heartbeat
 122         // Upon election: send initial empty AppendEntries RPCs
 123         // (heartbeat) to each server; repeat during idle periods to
 124         // prevent election timeouts (§5.2)
 125         sendAppendEntries(0, false);
 126
 127         // It is important to schedule this heartbeat here
 128         scheduleHeartBeat(context.getConfigParams().getHeartBeatInterval());
 129     }
 130
 131     protected AbstractLeader(RaftActorContext context, RaftState state) {
 132         this(context, state, null);
 133     }
 134
 135     /**
 136      * Return an immutable collection of follower identifiers.
 137      *
 138      * @return Collection of follower IDs
 139      */
 140     public final Collection<String> getFollowerIds() {
 141         return followerToLog.keySet();
 142     }
 143
 144     public void addFollower(String followerId) {
 145         FollowerLogInformation followerLogInformation = new FollowerLogInformationImpl(
 146                 context.getPeerInfo(followerId), -1, context);
 147         followerToLog.put(followerId, followerLogInformation);
 148
 149         if(heartbeatSchedule == null) {
 150             scheduleHeartBeat(context.getConfigParams().getHeartBeatInterval());
 151         }
 152     }
 153
 154     public void removeFollower(String followerId) {
 155         followerToLog.remove(followerId);
 156         mapFollowerToSnapshot.remove(followerId);
 157     }
 158
 159     public void updateMinReplicaCount() {
 160         int numVoting = 0;
 161         for(PeerInfo peer: context.getPeers()) {
 162             if(peer.isVoting()) {
 163                 numVoting++;
 164             }
 165         }
 166
 167         minReplicationCount = getMajorityVoteCount(numVoting);
 168     }
 169
 170     protected int getMinIsolatedLeaderPeerCount(){
 171       //the isolated Leader peer count will be 1 less than the majority vote count.
 172         //this is because the vote count has the self vote counted in it
 173         //for e.g
 174         //0 peers = 1 votesRequired , minIsolatedLeaderPeerCount = 0
 175         //2 peers = 2 votesRequired , minIsolatedLeaderPeerCount = 1
 176         //4 peers = 3 votesRequired, minIsolatedLeaderPeerCount = 2
 177
 178         return minReplicationCount > 0 ? (minReplicationCount - 1) : 0;
 179     }
 180
 181     @VisibleForTesting
 182     void setSnapshot(@Nullable Snapshot snapshot) {
 183         if(snapshot != null) {
 184             this.snapshot = Optional.of(new SnapshotHolder(snapshot));
 185         } else {
 186             this.snapshot = Optional.absent();
 187         }
 188     }
 189
 190     @Override
 191     protected RaftActorBehavior handleAppendEntries(ActorRef sender,
 192         AppendEntries appendEntries) {
 193
 194         LOG.debug("{}: handleAppendEntries: {}", logName(), appendEntries);
 195
 196         return this;
 197     }
 198
 199     @Override
 200     protected RaftActorBehavior handleAppendEntriesReply(ActorRef sender,
 201         AppendEntriesReply appendEntriesReply) {
 202
 203         if(LOG.isTraceEnabled()) {
 204             LOG.trace("{}: handleAppendEntriesReply: {}", logName(), appendEntriesReply);
 205         }
 206
 207         // Update the FollowerLogInformation
 208         String followerId = appendEntriesReply.getFollowerId();
 209         FollowerLogInformation followerLogInformation =
 210             followerToLog.get(followerId);
 211
 212         if(followerLogInformation == null){
 213             LOG.error("{}: handleAppendEntriesReply - unknown follower {}", logName(), followerId);
 214             return this;
 215         }
 216
 217         if(followerLogInformation.timeSinceLastActivity() >
 218                 context.getConfigParams().getElectionTimeOutInterval().toMillis()) {
 219             LOG.warn("{} : handleAppendEntriesReply delayed beyond election timeout, " +
 220                             "appendEntriesReply : {}, timeSinceLastActivity : {}, lastApplied : {}, commitIndex : {}",
 221                     logName(), appendEntriesReply, followerLogInformation.timeSinceLastActivity(),
 222                     context.getLastApplied(), context.getCommitIndex());
 223         }
 224
 225         followerLogInformation.markFollowerActive();
 226         followerLogInformation.setPayloadVersion(appendEntriesReply.getPayloadVersion());
 227         followerLogInformation.setRaftVersion(appendEntriesReply.getRaftVersion());
 228
 229         boolean updated = false;
 230         if(appendEntriesReply.getLogLastIndex() > context.getReplicatedLog().lastIndex()) {
 231             // The follower's log is actually ahead of the leader's log. Normally this doesn't happen
 232             // in raft as a node cannot become leader if it's log is behind another's. However, the
 233             // non-voting semantics deviate a bit from raft. Only voting members participate in
 234             // elections and can become leader so it's possible for a non-voting follower to be ahead
 235             // of the leader. This can happen if persistence is disabled and all voting members are
 236             // restarted. In this case, the voting leader will start out with an empty log however
 237             // the non-voting followers still retain the previous data in memory. On the first
 238             // AppendEntries, the non-voting follower returns a successful reply b/c the prevLogIndex
 239             // sent by the leader is -1 and thus the integrity checks pass. However the follower's returned
 240             // lastLogIndex may be higher in which case we want to reset the follower by installing a
 241             // snapshot. It's also possible that the follower's last log index is behind the leader's.
 242             // However in this case the log terms won't match and the logs will conflict - this is handled
 243             // elsewhere.
 244             LOG.debug("{}: handleAppendEntriesReply: follower {} lastIndex {} is ahead of our lastIndex {} - forcing install snaphot",
 245                     logName(), followerLogInformation.getId(), appendEntriesReply.getLogLastIndex(),
 246                     context.getReplicatedLog().lastIndex());
 247
 248             followerLogInformation.setMatchIndex(-1);
 249             followerLogInformation.setNextIndex(-1);
 250
 251             initiateCaptureSnapshot(followerId);
 252             updated = true;
 253         } else if (appendEntriesReply.isSuccess()) {
 254             updated = updateFollowerLogInformation(followerLogInformation, appendEntriesReply);
 255         } else {
 256             LOG.debug("{}: handleAppendEntriesReply: received unsuccessful reply: {}", logName(), appendEntriesReply);
 257
 258             long followerLastLogIndex = appendEntriesReply.getLogLastIndex();
 259             long followersLastLogTerm = getLogEntryTerm(followerLastLogIndex);
 260             if(appendEntriesReply.isForceInstallSnapshot()) {
 261                 // Reset the followers match and next index. This is to signal that this follower has nothing
 262                 // in common with this Leader and so would require a snapshot to be installed
 263                 followerLogInformation.setMatchIndex(-1);
 264                 followerLogInformation.setNextIndex(-1);
 265
 266                 // Force initiate a snapshot capture
 267                 initiateCaptureSnapshot(followerId);
 268             } else if(followerLastLogIndex < 0 || (followersLastLogTerm >= 0 &&
 269                     followersLastLogTerm == appendEntriesReply.getLogLastTerm())) {
 270                 // The follower's log is empty or the last entry is present in the leader's journal
 271                 // and the terms match so the follower is just behind the leader's journal from
 272                 // the last snapshot, if any. We'll catch up the follower quickly by starting at the
 273                 // follower's last log index.
 274
 275                 updated = updateFollowerLogInformation(followerLogInformation, appendEntriesReply);
 276             } else {
 277                 // The follower's log conflicts with leader's log so decrement follower's next index by 1
 278                 // in an attempt to find where the logs match.
 279
 280                 LOG.debug("{}: follower's last log term {} conflicts with the leader's {} - dec next index",
 281                         logName(), appendEntriesReply.getLogLastTerm(), followersLastLogTerm);
 282
 283                 followerLogInformation.decrNextIndex();
 284             }
 285         }
 286
 287         // Now figure out if this reply warrants a change in the commitIndex
 288         // If there exists an N such that N > commitIndex, a majority
 289         // of matchIndex[i] ≥ N, and log[N].term == currentTerm:
 290         // set commitIndex = N (§5.3, §5.4).
 291         if(LOG.isTraceEnabled()) {
 292             LOG.trace("{}: handleAppendEntriesReply from {}: commitIndex: {}, lastAppliedIndex: {}, currentTerm: {}",
 293                     logName(), followerId, context.getCommitIndex(), context.getLastApplied(), currentTerm());
 294         }
 295
 296         for (long N = context.getCommitIndex() + 1; ; N++) {
 297             int replicatedCount = 1;
 298
 299             LOG.trace("{}: checking Nth index {}", logName(), N);
 300             for (FollowerLogInformation info : followerToLog.values()) {
 301                 final PeerInfo peerInfo = context.getPeerInfo(info.getId());
 302                 if(info.getMatchIndex() >= N && (peerInfo != null && peerInfo.isVoting())) {
 303                     replicatedCount++;
 304                 } else if(LOG.isTraceEnabled()) {
 305                     LOG.trace("{}: Not counting follower {} - matchIndex: {}, {}", logName(), info.getId(),
 306                             info.getMatchIndex(), peerInfo);
 307                 }
 308             }
 309
 310             if(LOG.isTraceEnabled()) {
 311                 LOG.trace("{}: replicatedCount {}, minReplicationCount: {}", logName(), replicatedCount, minReplicationCount);
 312             }
 313
 314             if (replicatedCount >= minReplicationCount) {
 315                 ReplicatedLogEntry replicatedLogEntry = context.getReplicatedLog().get(N);
 316                 if (replicatedLogEntry == null) {
 317                     LOG.debug("{}: ReplicatedLogEntry not found for index {} - snapshotIndex: {}, journal size: {}",
 318                             logName(), N, context.getReplicatedLog().getSnapshotIndex(), context.getReplicatedLog().size());
 319                     break;
 320                 }
 321
 322                 // Don't update the commit index if the log entry is from a previous term, as per §5.4.1:
 323                 // "Raft never commits log entries from previous terms by counting replicas".
 324                 // However we keep looping so we can make progress when new entries in the current term
 325                 // reach consensus, as per §5.4.1: "once an entry from the current term is committed by
 326                 // counting replicas, then all prior entries are committed indirectly".
 327                 if (replicatedLogEntry.getTerm() == currentTerm()) {
 328                     LOG.trace("{}: Setting commit index to {}", logName(), N);
 329                     context.setCommitIndex(N);
 330                 } else {
 331                     LOG.debug("{}: Not updating commit index to {} - retrieved log entry with index {}, term {} does not match the current term {}",
 332                             logName(), N, replicatedLogEntry.getIndex(), replicatedLogEntry.getTerm(), currentTerm());
 333                 }
 334             } else {
 335                 LOG.trace("{}: minReplicationCount not reached, actual {} - breaking", logName(), replicatedCount);
 336                 break;
 337             }
 338         }
 339
 340         // Apply the change to the state machine
 341         if (context.getCommitIndex() > context.getLastApplied()) {
 342             if(LOG.isDebugEnabled()) {
 343                 LOG.debug("{}: handleAppendEntriesReply from {}: applying to log - commitIndex: {}, lastAppliedIndex: {}",
 344                         logName(), followerId, context.getCommitIndex(), context.getLastApplied());
 345             }
 346
 347             applyLogToStateMachine(context.getCommitIndex());
 348         }
 349
 350         if (!context.getSnapshotManager().isCapturing()) {
 351             purgeInMemoryLog();
 352         }
 353
 354         //Send the next log entry immediately, if possible, no need to wait for heartbeat to trigger that event
 355         sendUpdatesToFollower(followerId, followerLogInformation, false, !updated);
 356
 357         return this;
 358     }
 359
 360     private boolean updateFollowerLogInformation(FollowerLogInformation followerLogInformation,
 361             AppendEntriesReply appendEntriesReply) {
 362         boolean updated = followerLogInformation.setMatchIndex(appendEntriesReply.getLogLastIndex());
 363         updated = followerLogInformation.setNextIndex(appendEntriesReply.getLogLastIndex() + 1) || updated;
 364
 365         if(updated && LOG.isDebugEnabled()) {
 366             LOG.debug("{}: handleAppendEntriesReply - FollowerLogInformation for {} updated: matchIndex: {}, nextIndex: {}",
 367                     logName(), followerLogInformation.getId(), followerLogInformation.getMatchIndex(),
 368                     followerLogInformation.getNextIndex());
 369         }
 370         return updated;
 371     }
 372
 373     private void purgeInMemoryLog() {
 374         //find the lowest index across followers which has been replicated to all.
 375         // lastApplied if there are no followers, so that we keep clearing the log for single-node
 376         // we would delete the in-mem log from that index on, in-order to minimize mem usage
 377         // we would also share this info thru AE with the followers so that they can delete their log entries as well.
 378         long minReplicatedToAllIndex = followerToLog.isEmpty() ? context.getLastApplied() : Long.MAX_VALUE;
 379         for (FollowerLogInformation info : followerToLog.values()) {
 380             minReplicatedToAllIndex = Math.min(minReplicatedToAllIndex, info.getMatchIndex());
 381         }
 382
 383         super.performSnapshotWithoutCapture(minReplicatedToAllIndex);
 384     }
 385
 386     @Override
 387     protected ClientRequestTracker removeClientRequestTracker(long logIndex) {
 388         final Iterator<ClientRequestTracker> it = trackers.iterator();
 389         while (it.hasNext()) {
 390             final ClientRequestTracker t = it.next();
 391             if (t.getIndex() == logIndex) {
 392                 it.remove();
 393                 return t;
 394             }
 395         }
 396
 397         return null;
 398     }
 399
 400     @Override
 401     protected RaftActorBehavior handleRequestVoteReply(ActorRef sender,
 402         RequestVoteReply requestVoteReply) {
 403         return this;
 404     }
 405
 406     protected void beforeSendHeartbeat(){}
 407
 408     @Override
 409     public RaftActorBehavior handleMessage(ActorRef sender, Object message) {
 410         Preconditions.checkNotNull(sender, "sender should not be null");
 411
 412         if (message instanceof RaftRPC) {
 413             RaftRPC rpc = (RaftRPC) message;
 414             // If RPC request or response contains term T > currentTerm:
 415             // set currentTerm = T, convert to follower (§5.1)
 416             // This applies to all RPC messages and responses
 417             if (rpc.getTerm() > context.getTermInformation().getCurrentTerm()) {
 418                 LOG.debug("{}: Term {} in \"{}\" message is greater than leader's term {} - switching to Follower",
 419                         logName(), rpc.getTerm(), rpc, context.getTermInformation().getCurrentTerm());
 420
 421                 context.getTermInformation().updateAndPersist(rpc.getTerm(), null);
 422
 423                 return internalSwitchBehavior(RaftState.Follower);
 424             }
 425         }
 426
 427         if (message instanceof SendHeartBeat) {
 428             beforeSendHeartbeat();
 429             sendHeartBeat();
 430             scheduleHeartBeat(context.getConfigParams().getHeartBeatInterval());
 431         } else if(message instanceof SendInstallSnapshot) {
 432             // received from RaftActor
 433             setSnapshot(((SendInstallSnapshot) message).getSnapshot());
 434             sendInstallSnapshot();
 435         } else if (message instanceof Replicate) {
 436             replicate((Replicate) message);
 437         } else if (message instanceof InstallSnapshotReply) {
 438             handleInstallSnapshotReply((InstallSnapshotReply) message);
 439         } else {
 440             return super.handleMessage(sender, message);
 441         }
 442
 443         return this;
 444     }
 445
 446     private void handleInstallSnapshotReply(InstallSnapshotReply reply) {
 447         LOG.debug("{}: handleInstallSnapshotReply: {}", logName(), reply);
 448
 449         String followerId = reply.getFollowerId();
 450         FollowerToSnapshot followerToSnapshot = mapFollowerToSnapshot.get(followerId);
 451
 452         if (followerToSnapshot == null) {
 453             LOG.error("{}: FollowerToSnapshot not found for follower {} in InstallSnapshotReply",
 454                     logName(), followerId);
 455             return;
 456         }
 457
 458         FollowerLogInformation followerLogInformation = followerToLog.get(followerId);
 459         if(followerLogInformation == null) {
 460             // This can happen during AddServer if it times out.
 461             LOG.error("{}: FollowerLogInformation not found for follower {} in InstallSnapshotReply",
 462                     logName(), followerId);
 463             mapFollowerToSnapshot.remove(followerId);
 464             return;
 465         }
 466
 467         followerLogInformation.markFollowerActive();
 468
 469         if (followerToSnapshot.getChunkIndex() == reply.getChunkIndex()) {
 470             boolean wasLastChunk = false;
 471             if (reply.isSuccess()) {
 472                 if(followerToSnapshot.isLastChunk(reply.getChunkIndex())) {
 473                     //this was the last chunk reply
 474                     if(LOG.isDebugEnabled()) {
 475                         LOG.debug("{}: InstallSnapshotReply received, " +
 476                                 "last chunk received, Chunk: {}. Follower: {} Setting nextIndex: {}",
 477                                 logName(), reply.getChunkIndex(), followerId,
 478                             context.getReplicatedLog().getSnapshotIndex() + 1
 479                         );
 480                     }
 481
 482                     long followerMatchIndex = snapshot.get().getLastIncludedIndex();
 483                     followerLogInformation.setMatchIndex(followerMatchIndex);
 484                     followerLogInformation.setNextIndex(followerMatchIndex + 1);
 485                     mapFollowerToSnapshot.remove(followerId);
 486
 487                     LOG.debug("{}: follower: {}, matchIndex set to {}, nextIndex set to {}",
 488                         logName(), followerId, followerLogInformation.getMatchIndex(),
 489                         followerLogInformation.getNextIndex());
 490
 491                     if (mapFollowerToSnapshot.isEmpty()) {
 492                         // once there are no pending followers receiving snapshots
 493                         // we can remove snapshot from the memory
 494                         setSnapshot(null);
 495                     }
 496                     wasLastChunk = true;
 497                     if(context.getPeerInfo(followerId).getVotingState() == VotingState.VOTING_NOT_INITIALIZED){
 498                         UnInitializedFollowerSnapshotReply unInitFollowerSnapshotSuccess =
 499                                              new UnInitializedFollowerSnapshotReply(followerId);
 500                         context.getActor().tell(unInitFollowerSnapshotSuccess, context.getActor());
 501                         LOG.debug("Sent message UnInitializedFollowerSnapshotReply to self");
 502                     }
 503                 } else {
 504                     followerToSnapshot.markSendStatus(true);
 505                 }
 506             } else {
 507                 LOG.info("{}: InstallSnapshotReply received sending snapshot chunk failed, Will retry, Chunk: {}",
 508                         logName(), reply.getChunkIndex());
 509
 510                 followerToSnapshot.markSendStatus(false);
 511             }
 512
 513             if (wasLastChunk && !context.getSnapshotManager().isCapturing()) {
 514                 // Since the follower is now caught up try to purge the log.
 515                 purgeInMemoryLog();
 516             } else if (!wasLastChunk && followerToSnapshot.canSendNextChunk()) {
 517                 ActorSelection followerActor = context.getPeerActorSelection(followerId);
 518                 if(followerActor != null) {
 519                     sendSnapshotChunk(followerActor, followerId);
 520                 }
 521             }
 522
 523         } else {
 524             LOG.error("{}: Chunk index {} in InstallSnapshotReply from follower {} does not match expected index {}",
 525                     logName(), reply.getChunkIndex(), followerId,
 526                     followerToSnapshot.getChunkIndex());
 527
 528             if(reply.getChunkIndex() == INVALID_CHUNK_INDEX){
 529                 // Since the Follower did not find this index to be valid we should reset the follower snapshot
 530                 // so that Installing the snapshot can resume from the beginning
 531                 followerToSnapshot.reset();
 532             }
 533         }
 534     }
 535
 536     private void replicate(Replicate replicate) {
 537         long logIndex = replicate.getReplicatedLogEntry().getIndex();
 538
 539         LOG.debug("{}: Replicate message: identifier: {}, logIndex: {}, payload: {}", logName(),
 540                 replicate.getIdentifier(), logIndex, replicate.getReplicatedLogEntry().getData().getClass());
 541
 542         // Create a tracker entry we will use this later to notify the
 543         // client actor
 544         if(replicate.getClientActor() != null) {
 545             trackers.add(new ClientRequestTrackerImpl(replicate.getClientActor(), replicate.getIdentifier(),
 546                     logIndex));
 547         }
 548
 549         boolean applyModificationToState = !context.anyVotingPeers()
 550                 || context.getRaftPolicy().applyModificationToStateBeforeConsensus();
 551
 552         if(applyModificationToState){
 553             context.setCommitIndex(logIndex);
 554             applyLogToStateMachine(logIndex);
 555         }
 556
 557         if (!followerToLog.isEmpty()) {
 558             sendAppendEntries(0, false);
 559         }
 560     }
 561
 562     protected void sendAppendEntries(long timeSinceLastActivityInterval, boolean isHeartbeat) {
 563         // Send an AppendEntries to all followers
 564         for (Entry<String, FollowerLogInformation> e : followerToLog.entrySet()) {
 565             final String followerId = e.getKey();
 566             final FollowerLogInformation followerLogInformation = e.getValue();
 567             // This checks helps not to send a repeat message to the follower
 568             if(!followerLogInformation.isFollowerActive() ||
 569                     followerLogInformation.timeSinceLastActivity() >= timeSinceLastActivityInterval) {
 570                 sendUpdatesToFollower(followerId, followerLogInformation, true, isHeartbeat);
 571             }
 572         }
 573     }
 574
 575     /**
 576      *
 577      * This method checks if any update needs to be sent to the given follower. This includes append log entries,
 578      * sending next snapshot chunk, and initiating a snapshot.
 579      * @return true if any update is sent, false otherwise
 580      */
 581
 582     private void sendUpdatesToFollower(String followerId, FollowerLogInformation followerLogInformation,
 583                                        boolean sendHeartbeat, boolean isHeartbeat) {
 584
 585         ActorSelection followerActor = context.getPeerActorSelection(followerId);
 586         if (followerActor != null) {
 587             long followerNextIndex = followerLogInformation.getNextIndex();
 588             boolean isFollowerActive = followerLogInformation.isFollowerActive();
 589             boolean sendAppendEntries = false;
 590             List<ReplicatedLogEntry> entries = Collections.emptyList();
 591
 592             if (mapFollowerToSnapshot.get(followerId) != null) {
 593                 // if install snapshot is in process , then sent next chunk if possible
 594                 if (isFollowerActive && mapFollowerToSnapshot.get(followerId).canSendNextChunk()) {
 595                     sendSnapshotChunk(followerActor, followerId);
 596                 } else if(sendHeartbeat) {
 597                     // we send a heartbeat even if we have not received a reply for the last chunk
 598                     sendAppendEntries = true;
 599                 }
 600             } else {
 601                 long leaderLastIndex = context.getReplicatedLog().lastIndex();
 602                 long leaderSnapShotIndex = context.getReplicatedLog().getSnapshotIndex();
 603
 604                 if((!isHeartbeat && LOG.isDebugEnabled()) || LOG.isTraceEnabled()) {
 605                     LOG.debug("{}: Checking sendAppendEntries for follower {}: active: {}, followerNextIndex: {}, leaderLastIndex: {}, leaderSnapShotIndex: {}",
 606                             logName(), followerId, isFollowerActive, followerNextIndex, leaderLastIndex, leaderSnapShotIndex);
 607                 }
 608
 609                 if (isFollowerActive && context.getReplicatedLog().isPresent(followerNextIndex)) {
 610
 611                     LOG.debug("{}: sendAppendEntries: {} is present for follower {}", logName(),
 612                             followerNextIndex, followerId);
 613
 614                     if(followerLogInformation.okToReplicate()) {
 615                         // Try to send all the entries in the journal but not exceeding the max data size
 616                         // for a single AppendEntries message.
 617                         int maxEntries = (int) context.getReplicatedLog().size();
 618                         entries = context.getReplicatedLog().getFrom(followerNextIndex, maxEntries,
 619                                 context.getConfigParams().getSnapshotChunkSize());
 620                         sendAppendEntries = true;
 621                     }
 622                 } else if (isFollowerActive && followerNextIndex >= 0 &&
 623                     leaderLastIndex > followerNextIndex && !context.getSnapshotManager().isCapturing()) {
 624                     // if the followers next index is not present in the leaders log, and
 625                     // if the follower is just not starting and if leader's index is more than followers index
 626                     // then snapshot should be sent
 627
 628                     if (LOG.isDebugEnabled()) {
 629                         LOG.debug(String.format("%s: InitiateInstallSnapshot to follower: %s, " +
 630                                     "follower-nextIndex: %d, leader-snapshot-index: %d,  " +
 631                                     "leader-last-index: %d", logName(), followerId,
 632                                     followerNextIndex, leaderSnapShotIndex, leaderLastIndex));
 633                     }
 634
 635                     // Send heartbeat to follower whenever install snapshot is initiated.
 636                     sendAppendEntries = true;
 637                     if (canInstallSnapshot(followerNextIndex)) {
 638                         initiateCaptureSnapshot(followerId);
 639                     }
 640
 641                 } else if(sendHeartbeat) {
 642                     // we send an AppendEntries, even if the follower is inactive
 643                     // in-order to update the followers timestamp, in case it becomes active again
 644                     sendAppendEntries = true;
 645                 }
 646
 647             }
 648
 649             if(sendAppendEntries) {
 650                 sendAppendEntriesToFollower(followerActor, followerNextIndex,
 651                         entries, followerId);
 652             }
 653         }
 654     }
 655
 656     private void sendAppendEntriesToFollower(ActorSelection followerActor, long followerNextIndex,
 657         List<ReplicatedLogEntry> entries, String followerId) {
 658         AppendEntries appendEntries = new AppendEntries(currentTerm(), context.getId(),
 659             getLogEntryIndex(followerNextIndex - 1),
 660             getLogEntryTerm(followerNextIndex - 1), entries,
 661             context.getCommitIndex(), super.getReplicatedToAllIndex(), context.getPayloadVersion());
 662
 663         if(!entries.isEmpty() || LOG.isTraceEnabled()) {
 664             LOG.debug("{}: Sending AppendEntries to follower {}: {}", logName(), followerId,
 665                     appendEntries);
 666         }
 667
 668         followerActor.tell(appendEntries, actor());
 669     }
 670
 671     /**
 672      * Install Snapshot works as follows
 673      * 1. Leader initiates the capture snapshot by sending a CaptureSnapshot message to actor
 674      * 2. RaftActor on receipt of the CaptureSnapshotReply (from Shard), stores the received snapshot in the replicated log
 675      * and makes a call to Leader's handleMessage , with SendInstallSnapshot message.
 676      * 3. Leader , picks the snapshot from im-mem ReplicatedLog and sends it in chunks to the Follower
 677      * 4. On complete, Follower sends back a InstallSnapshotReply.
 678      * 5. On receipt of the InstallSnapshotReply for the last chunk, Leader marks the install complete for that follower
 679      * and replenishes the memory by deleting the snapshot in Replicated log.
 680      * 6. If another follower requires a snapshot and a snapshot has been collected (via CaptureSnapshotReply)
 681      * then send the existing snapshot in chunks to the follower.
 682      * @param followerId
 683      */
 684     public boolean initiateCaptureSnapshot(String followerId) {
 685         if (snapshot.isPresent()) {
 686             // if a snapshot is present in the memory, most likely another install is in progress
 687             // no need to capture snapshot.
 688             // This could happen if another follower needs an install when one is going on.
 689             final ActorSelection followerActor = context.getPeerActorSelection(followerId);
 690             sendSnapshotChunk(followerActor, followerId);
 691             return true;
 692         } else {
 693             return context.getSnapshotManager().captureToInstall(context.getReplicatedLog().last(),
 694                     this.getReplicatedToAllIndex(), followerId);
 695         }
 696     }
 697
 698     private boolean canInstallSnapshot(long nextIndex){
 699         // If the follower's nextIndex is -1 then we might as well send it a snapshot
 700         // Otherwise send it a snapshot only if the nextIndex is not present in the log but is present
 701         // in the snapshot
 702         return (nextIndex == -1 ||
 703                 (!context.getReplicatedLog().isPresent(nextIndex)
 704                         && context.getReplicatedLog().isInSnapshot(nextIndex)));
 705
 706     }
 707
 708
 709     private void sendInstallSnapshot() {
 710         LOG.debug("{}: sendInstallSnapshot", logName());
 711         for (Entry<String, FollowerLogInformation> e : followerToLog.entrySet()) {
 712             String followerId = e.getKey();
 713             ActorSelection followerActor = context.getPeerActorSelection(followerId);
 714             FollowerLogInformation followerLogInfo = e.getValue();
 715
 716             if (followerActor != null) {
 717                 long nextIndex = followerLogInfo.getNextIndex();
 718                 if (context.getPeerInfo(followerId).getVotingState() == VotingState.VOTING_NOT_INITIALIZED ||
 719                         canInstallSnapshot(nextIndex)) {
 720                     sendSnapshotChunk(followerActor, followerId);
 721                 }
 722             }
 723         }
 724     }
 725
 726     /**
 727      *  Sends a snapshot chunk to a given follower
 728      *  InstallSnapshot should qualify as a heartbeat too.
 729      */
 730     private void sendSnapshotChunk(ActorSelection followerActor, String followerId) {
 731         try {
 732             if (snapshot.isPresent()) {
 733                 byte[] nextSnapshotChunk = getNextSnapshotChunk(followerId, snapshot.get().getSnapshotBytes());
 734
 735                 // Note: the previous call to getNextSnapshotChunk has the side-effect of adding
 736                 // followerId to the followerToSnapshot map.
 737                 FollowerToSnapshot followerToSnapshot = mapFollowerToSnapshot.get(followerId);
 738
 739                 int nextChunkIndex = followerToSnapshot.incrementChunkIndex();
 740                 Optional<ServerConfigurationPayload> serverConfig = Optional.absent();
 741                 if(followerToSnapshot.isLastChunk(nextChunkIndex)) {
 742                     serverConfig = Optional.fromNullable(context.getPeerServerInfo(true));
 743                 }
 744
 745                 followerActor.tell(
 746                     new InstallSnapshot(currentTerm(), context.getId(),
 747                         snapshot.get().getLastIncludedIndex(),
 748                         snapshot.get().getLastIncludedTerm(),
 749                         nextSnapshotChunk,
 750                         nextChunkIndex,
 751                         followerToSnapshot.getTotalChunks(),
 752                         Optional.of(followerToSnapshot.getLastChunkHashCode()),
 753                         serverConfig
 754                     ).toSerializable(followerToLog.get(followerId).getRaftVersion()),
 755                     actor()
 756                 );
 757
 758                 if(LOG.isDebugEnabled()) {
 759                     LOG.debug("{}: InstallSnapshot sent to follower {}, Chunk: {}/{}",
 760                             logName(), followerActor.path(), followerToSnapshot.getChunkIndex(),
 761                             followerToSnapshot.getTotalChunks());
 762                 }
 763             }
 764         } catch (IOException e) {
 765             LOG.error("{}: InstallSnapshot failed for Leader.", logName(), e);
 766         }
 767     }
 768
 769     /**
 770      * Acccepts snaphot as ByteString, enters into map for future chunks
 771      * creates and return a ByteString chunk
 772      */
 773     private byte[] getNextSnapshotChunk(String followerId, ByteString snapshotBytes) throws IOException {
 774         FollowerToSnapshot followerToSnapshot = mapFollowerToSnapshot.get(followerId);
 775         if (followerToSnapshot == null) {
 776             followerToSnapshot = new FollowerToSnapshot(snapshotBytes);
 777             mapFollowerToSnapshot.put(followerId, followerToSnapshot);
 778         }
 779         byte[] nextChunk = followerToSnapshot.getNextChunk();
 780
 781         LOG.debug("{}: next snapshot chunk size for follower {}: {}", logName(), followerId, nextChunk.length);
 782
 783         return nextChunk;
 784     }
 785
 786     private void sendHeartBeat() {
 787         if (!followerToLog.isEmpty()) {
 788             LOG.trace("{}: Sending heartbeat", logName());
 789             sendAppendEntries(context.getConfigParams().getHeartBeatInterval().toMillis(), true);
 790         }
 791     }
 792
 793     private void stopHeartBeat() {
 794         if (heartbeatSchedule != null && !heartbeatSchedule.isCancelled()) {
 795             heartbeatSchedule.cancel();
 796         }
 797     }
 798
 799     private void scheduleHeartBeat(FiniteDuration interval) {
 800         if (followerToLog.isEmpty()) {
 801             // Optimization - do not bother scheduling a heartbeat as there are
 802             // no followers
 803             return;
 804         }
 805
 806         stopHeartBeat();
 807
 808         // Schedule a heartbeat. When the scheduler triggers a SendHeartbeat
 809         // message is sent to itself.
 810         // Scheduling the heartbeat only once here because heartbeats do not
 811         // need to be sent if there are other messages being sent to the remote
 812         // actor.
 813         heartbeatSchedule = context.getActorSystem().scheduler().scheduleOnce(
 814             interval, context.getActor(), SendHeartBeat.INSTANCE,
 815             context.getActorSystem().dispatcher(), context.getActor());
 816     }
 817
 818     @Override
 819     public void close() {
 820         stopHeartBeat();
 821     }
 822
 823     @Override
 824     public final String getLeaderId() {
 825         return context.getId();
 826     }
 827
 828     @Override
 829     public final short getLeaderPayloadVersion() {
 830         return context.getPayloadVersion();
 831     }
 832
 833     protected boolean isLeaderIsolated() {
 834         int minPresent = getMinIsolatedLeaderPeerCount();
 835         for (FollowerLogInformation followerLogInformation : followerToLog.values()) {
 836             final PeerInfo peerInfo = context.getPeerInfo(followerLogInformation.getId());
 837             if(peerInfo != null && peerInfo.isVoting() && followerLogInformation.isFollowerActive()) {
 838                 --minPresent;
 839                 if (minPresent == 0) {
 840                     return false;
 841                 }
 842             }
 843         }
 844         return (minPresent != 0);
 845     }
 846
 847     /**
 848      * Encapsulates the snapshot bytestring and handles the logic of sending
 849      * snapshot chunks
 850      */
 851     protected class FollowerToSnapshot {
 852         private final ByteString snapshotBytes;
 853         private int offset = 0;
 854         // the next snapshot chunk is sent only if the replyReceivedForOffset matches offset
 855         private int replyReceivedForOffset;
 856         // if replyStatus is false, the previous chunk is attempted
 857         private boolean replyStatus = false;
 858         private int chunkIndex;
 859         private final int totalChunks;
 860         private int lastChunkHashCode = AbstractLeader.INITIAL_LAST_CHUNK_HASH_CODE;
 861         private int nextChunkHashCode = AbstractLeader.INITIAL_LAST_CHUNK_HASH_CODE;
 862
 863         public FollowerToSnapshot(ByteString snapshotBytes) {
 864             this.snapshotBytes = snapshotBytes;
 865             int size = snapshotBytes.size();
 866             totalChunks = ( size / context.getConfigParams().getSnapshotChunkSize()) +
 867                 ((size % context.getConfigParams().getSnapshotChunkSize()) > 0 ? 1 : 0);
 868             if(LOG.isDebugEnabled()) {
 869                 LOG.debug("{}: Snapshot {} bytes, total chunks to send:{}",
 870                         logName(), size, totalChunks);
 871             }
 872             replyReceivedForOffset = -1;
 873             chunkIndex = AbstractLeader.FIRST_CHUNK_INDEX;
 874         }
 875
 876         public ByteString getSnapshotBytes() {
 877             return snapshotBytes;
 878         }
 879
 880         public int incrementOffset() {
 881             if(replyStatus) {
 882                 // if prev chunk failed, we would want to sent the same chunk again
 883                 offset = offset + context.getConfigParams().getSnapshotChunkSize();
 884             }
 885             return offset;
 886         }
 887
 888         public int incrementChunkIndex() {
 889             if (replyStatus) {
 890                 // if prev chunk failed, we would want to sent the same chunk again
 891                 chunkIndex =  chunkIndex + 1;
 892             }
 893             return chunkIndex;
 894         }
 895
 896         public int getChunkIndex() {
 897             return chunkIndex;
 898         }
 899
 900         public int getTotalChunks() {
 901             return totalChunks;
 902         }
 903
 904         public boolean canSendNextChunk() {
 905             // we only send a false if a chunk is sent but we have not received a reply yet
 906             return replyReceivedForOffset == offset;
 907         }
 908
 909         public boolean isLastChunk(int chunkIndex) {
 910             return totalChunks == chunkIndex;
 911         }
 912
 913         public void markSendStatus(boolean success) {
 914             if (success) {
 915                 // if the chunk sent was successful
 916                 replyReceivedForOffset = offset;
 917                 replyStatus = true;
 918                 lastChunkHashCode = nextChunkHashCode;
 919             } else {
 920                 // if the chunk sent was failure
 921                 replyReceivedForOffset = offset;
 922                 replyStatus = false;
 923             }
 924         }
 925
 926         public byte[] getNextChunk() {
 927             int snapshotLength = getSnapshotBytes().size();
 928             int start = incrementOffset();
 929             int size = context.getConfigParams().getSnapshotChunkSize();
 930             if (context.getConfigParams().getSnapshotChunkSize() > snapshotLength) {
 931                 size = snapshotLength;
 932             } else if ((start + context.getConfigParams().getSnapshotChunkSize()) > snapshotLength) {
 933                 size = snapshotLength - start;
 934             }
 935
 936             byte[] nextChunk = new byte[size];
 937             getSnapshotBytes().copyTo(nextChunk, start, 0, size);
 938             nextChunkHashCode = Arrays.hashCode(nextChunk);
 939
 940             LOG.debug("{}: Next chunk: total length={}, offset={}, size={}, hashCode={}", logName(),
 941                     snapshotLength, start, size, nextChunkHashCode);
 942             return nextChunk;
 943         }
 944
 945         /**
 946          * reset should be called when the Follower needs to be sent the snapshot from the beginning
 947          */
 948         public void reset(){
 949             offset = 0;
 950             replyStatus = false;
 951             replyReceivedForOffset = offset;
 952             chunkIndex = AbstractLeader.FIRST_CHUNK_INDEX;
 953             lastChunkHashCode = AbstractLeader.INITIAL_LAST_CHUNK_HASH_CODE;
 954         }
 955
 956         public int getLastChunkHashCode() {
 957             return lastChunkHashCode;
 958         }
 959     }
 960
 961     // called from example-actor for printing the follower-states
 962     public String printFollowerStates() {
 963         final StringBuilder sb = new StringBuilder();
 964
 965         sb.append('[');
 966         for (FollowerLogInformation followerLogInformation : followerToLog.values()) {
 967             sb.append('{');
 968             sb.append(followerLogInformation.getId());
 969             sb.append(" state:");
 970             sb.append(followerLogInformation.isFollowerActive());
 971             sb.append("},");
 972         }
 973         sb.append(']');
 974
 975         return sb.toString();
 976     }
 977
 978     @VisibleForTesting
 979     public FollowerLogInformation getFollower(String followerId) {
 980         return followerToLog.get(followerId);
 981     }
 982
 983     @VisibleForTesting
 984     protected void setFollowerSnapshot(String followerId, FollowerToSnapshot snapshot) {
 985         mapFollowerToSnapshot.put(followerId, snapshot);
 986     }
 987
 988     @VisibleForTesting
 989     public int followerSnapshotSize() {
 990         return mapFollowerToSnapshot.size();
 991     }
 992
 993     @VisibleForTesting
 994     public int followerLogSize() {
 995         return followerToLog.size();
 996     }
 997
 998     private static class SnapshotHolder {
 999         private final long lastIncludedTerm;
1000         private final long lastIncludedIndex;
1001         private final ByteString snapshotBytes;
1002
1003         SnapshotHolder(Snapshot snapshot) {
1004             this.lastIncludedTerm = snapshot.getLastAppliedTerm();
1005             this.lastIncludedIndex = snapshot.getLastAppliedIndex();
1006             this.snapshotBytes = ByteString.copyFrom(snapshot.getState());
1007         }
1008
1009         long getLastIncludedTerm() {
1010             return lastIncludedTerm;
1011         }
1012
1013         long getLastIncludedIndex() {
1014             return lastIncludedIndex;
1015         }
1016
1017         ByteString getSnapshotBytes() {
1018             return snapshotBytes;
1019         }
1020     }
1021 }