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