Bug 6540: Fix journal issues on leader changes
[controller.git] / opendaylight / md-sal / sal-akka-raft / src / main / java / org / opendaylight / controller / cluster / raft / behaviors / Follower.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.Address;
14 import akka.cluster.Cluster;
15 import akka.cluster.ClusterEvent.CurrentClusterState;
16 import akka.cluster.Member;
17 import akka.cluster.MemberStatus;
18 import akka.japi.Procedure;
19 import com.google.common.annotations.VisibleForTesting;
20 import com.google.common.base.Stopwatch;
21 import java.util.ArrayList;
22 import java.util.Optional;
23 import java.util.Set;
24 import java.util.concurrent.TimeUnit;
25 import javax.annotation.Nullable;
26 import org.opendaylight.controller.cluster.raft.RaftActorContext;
27 import org.opendaylight.controller.cluster.raft.RaftState;
28 import org.opendaylight.controller.cluster.raft.ReplicatedLogEntry;
29 import org.opendaylight.controller.cluster.raft.Snapshot;
30 import org.opendaylight.controller.cluster.raft.base.messages.ApplySnapshot;
31 import org.opendaylight.controller.cluster.raft.base.messages.ElectionTimeout;
32 import org.opendaylight.controller.cluster.raft.base.messages.TimeoutNow;
33 import org.opendaylight.controller.cluster.raft.messages.AppendEntries;
34 import org.opendaylight.controller.cluster.raft.messages.AppendEntriesReply;
35 import org.opendaylight.controller.cluster.raft.messages.InstallSnapshot;
36 import org.opendaylight.controller.cluster.raft.messages.InstallSnapshotReply;
37 import org.opendaylight.controller.cluster.raft.messages.RaftRPC;
38 import org.opendaylight.controller.cluster.raft.messages.RequestVote;
39 import org.opendaylight.controller.cluster.raft.messages.RequestVoteReply;
40 import org.opendaylight.controller.cluster.raft.persisted.ServerConfigurationPayload;
41
42 /**
43  * The behavior of a RaftActor in the Follower state
44  * <p/>
45  * <ul>
46  * <li> Respond to RPCs from candidates and leaders
47  * <li> If election timeout elapses without receiving AppendEntries
48  * RPC from current leader or granting vote to candidate:
49  * convert to candidate
50  * </ul>
51  */
52 public class Follower extends AbstractRaftActorBehavior {
53     private static final int SYNC_THRESHOLD = 10;
54
55     private static final long MAX_ELECTION_TIMEOUT_FACTOR = 18;
56
57     private final SyncStatusTracker initialSyncStatusTracker;
58
59     private final Procedure<ReplicatedLogEntry> appendAndPersistCallback =
60             logEntry -> context.getReplicatedLog().captureSnapshotIfReady(logEntry);
61
62     private final Stopwatch lastLeaderMessageTimer = Stopwatch.createStarted();
63     private SnapshotTracker snapshotTracker = null;
64     private String leaderId;
65     private short leaderPayloadVersion;
66
67     public Follower(RaftActorContext context) {
68         this(context, null, (short)-1);
69     }
70
71     public Follower(RaftActorContext context, String initialLeaderId, short initialLeaderPayloadVersion) {
72         super(context, RaftState.Follower);
73         this.leaderId = initialLeaderId;
74         this.leaderPayloadVersion = initialLeaderPayloadVersion;
75
76         initialSyncStatusTracker = new SyncStatusTracker(context.getActor(), getId(), SYNC_THRESHOLD);
77
78         if (context.getPeerIds().isEmpty() && getLeaderId() == null) {
79             actor().tell(TimeoutNow.INSTANCE, actor());
80         } else {
81             scheduleElection(electionDuration());
82         }
83     }
84
85     @Override
86     public final String getLeaderId() {
87         return leaderId;
88     }
89
90     @VisibleForTesting
91     protected final void setLeaderId(@Nullable final String leaderId) {
92         this.leaderId = leaderId;
93     }
94
95     @Override
96     public short getLeaderPayloadVersion() {
97         return leaderPayloadVersion;
98     }
99
100     @VisibleForTesting
101     protected final void setLeaderPayloadVersion(short leaderPayloadVersion) {
102         this.leaderPayloadVersion = leaderPayloadVersion;
103     }
104
105     private void restartLastLeaderMessageTimer() {
106         if (lastLeaderMessageTimer.isRunning()) {
107             lastLeaderMessageTimer.reset();
108         }
109
110         lastLeaderMessageTimer.start();
111     }
112
113     private boolean isLogEntryPresent(long index){
114         if(context.getReplicatedLog().isInSnapshot(index)) {
115             return true;
116         }
117
118         ReplicatedLogEntry entry = context.getReplicatedLog().get(index);
119         return entry != null;
120
121     }
122
123     private void updateInitialSyncStatus(long currentLeaderCommit, String leaderId){
124         initialSyncStatusTracker.update(leaderId, currentLeaderCommit, context.getCommitIndex());
125     }
126
127     @Override
128     protected RaftActorBehavior handleAppendEntries(ActorRef sender, AppendEntries appendEntries) {
129
130         int numLogEntries = appendEntries.getEntries() != null ? appendEntries.getEntries().size() : 0;
131         if(LOG.isTraceEnabled()) {
132             LOG.trace("{}: handleAppendEntries: {}", logName(), appendEntries);
133         } else if(LOG.isDebugEnabled() && numLogEntries > 0) {
134             LOG.debug("{}: handleAppendEntries: {}", logName(), appendEntries);
135         }
136
137         // TODO : Refactor this method into a bunch of smaller methods
138         // to make it easier to read. Before refactoring ensure tests
139         // cover the code properly
140
141         if (snapshotTracker != null && !snapshotTracker.getLeaderId().equals(appendEntries.getLeaderId())) {
142             LOG.debug("{}: snapshot install is in progress but the prior snapshot leaderId {} does not match the " +
143                     "AppendEntries leaderId {}", logName(), snapshotTracker.getLeaderId(), appendEntries.getLeaderId());
144             snapshotTracker = null;
145         }
146
147         if (snapshotTracker != null || context.getSnapshotManager().isApplying()) {
148             // if snapshot install is in progress, follower should just acknowledge append entries with a reply.
149             AppendEntriesReply reply = new AppendEntriesReply(context.getId(), currentTerm(), true,
150                     lastIndex(), lastTerm(), context.getPayloadVersion());
151
152             if(LOG.isDebugEnabled()) {
153                 LOG.debug("{}: snapshot install is in progress, replying immediately with {}", logName(), reply);
154             }
155             sender.tell(reply, actor());
156
157             return this;
158         }
159
160         // If we got here then we do appear to be talking to the leader
161         leaderId = appendEntries.getLeaderId();
162         leaderPayloadVersion = appendEntries.getPayloadVersion();
163
164         updateInitialSyncStatus(appendEntries.getLeaderCommit(), appendEntries.getLeaderId());
165         // First check if the logs are in sync or not
166         long lastIndex = lastIndex();
167
168         if (isOutOfSync(appendEntries)) {
169             // We found that the log was out of sync so just send a negative
170             // reply and return
171
172             LOG.debug("{}: Follower is out-of-sync, so sending negative reply, lastIndex: {}, lastTerm: {}",
173                         logName(), lastIndex, lastTerm());
174
175             sender.tell(new AppendEntriesReply(context.getId(), currentTerm(), false, lastIndex,
176                     lastTerm(), context.getPayloadVersion()), actor());
177             return this;
178         }
179
180         if (appendEntries.getEntries() != null && appendEntries.getEntries().size() > 0) {
181
182             LOG.debug("{}: Number of entries to be appended = {}", logName(),
183                         appendEntries.getEntries().size());
184
185             // 3. If an existing entry conflicts with a new one (same index
186             // but different terms), delete the existing entry and all that
187             // follow it (§5.3)
188             int addEntriesFrom = 0;
189             if (context.getReplicatedLog().size() > 0) {
190
191                 // Find the entry up until the one that is not in the follower's log
192                 for (int i = 0;i < appendEntries.getEntries().size(); i++, addEntriesFrom++) {
193                     ReplicatedLogEntry matchEntry = appendEntries.getEntries().get(i);
194
195                     if(!isLogEntryPresent(matchEntry.getIndex())) {
196                         // newEntry not found in the log
197                         break;
198                     }
199
200                     long existingEntryTerm = getLogEntryTerm(matchEntry.getIndex());
201
202                     LOG.debug("{}: matchEntry {} is present: existingEntryTerm: {}", logName(), matchEntry,
203                             existingEntryTerm);
204
205                     // existingEntryTerm == -1 means it's in the snapshot and not in the log. We don't know
206                     // what the term was so we'll assume it matches.
207                     if(existingEntryTerm == -1 || existingEntryTerm == matchEntry.getTerm()) {
208                         continue;
209                     }
210
211                     if(!context.getRaftPolicy().applyModificationToStateBeforeConsensus()) {
212
213                         LOG.debug("{}: Removing entries from log starting at {}", logName(),
214                                 matchEntry.getIndex());
215
216                         // Entries do not match so remove all subsequent entries
217                         if(!context.getReplicatedLog().removeFromAndPersist(matchEntry.getIndex())) {
218                             // Could not remove the entries - this means the matchEntry index must be in the
219                             // snapshot and not the log. In this case the prior entries are part of the state
220                             // so we must send back a reply to force a snapshot to completely re-sync the
221                             // follower's log and state.
222
223                             LOG.debug("{}: Could not remove entries - sending reply to force snapshot", logName());
224                             sender.tell(new AppendEntriesReply(context.getId(), currentTerm(), false, lastIndex,
225                                     lastTerm(), context.getPayloadVersion(), true), actor());
226                             return this;
227                         }
228
229                         break;
230                     } else {
231                         sender.tell(new AppendEntriesReply(context.getId(), currentTerm(), false, lastIndex,
232                                 lastTerm(), context.getPayloadVersion(), true), actor());
233                         return this;
234                     }
235                 }
236             }
237
238             lastIndex = lastIndex();
239             LOG.debug("{}: After cleanup, lastIndex: {}, entries to be added from: {}", logName(),
240                     lastIndex, addEntriesFrom);
241
242             // 4. Append any new entries not already in the log
243             for (int i = addEntriesFrom; i < appendEntries.getEntries().size(); i++) {
244                 ReplicatedLogEntry entry = appendEntries.getEntries().get(i);
245
246                 LOG.debug("{}: Append entry to log {}", logName(), entry.getData());
247
248                 context.getReplicatedLog().appendAndPersist(entry, appendAndPersistCallback);
249
250                 if(entry.getData() instanceof ServerConfigurationPayload) {
251                     context.updatePeerIds((ServerConfigurationPayload)entry.getData());
252                 }
253             }
254
255             LOG.debug("{}: Log size is now {}", logName(), context.getReplicatedLog().size());
256         }
257
258         // 5. If leaderCommit > commitIndex, set commitIndex =
259         // min(leaderCommit, index of last new entry)
260
261         lastIndex = lastIndex();
262         long prevCommitIndex = context.getCommitIndex();
263
264         if(appendEntries.getLeaderCommit() > prevCommitIndex) {
265             context.setCommitIndex(Math.min(appendEntries.getLeaderCommit(), lastIndex));
266         }
267
268         if (prevCommitIndex != context.getCommitIndex()) {
269             LOG.debug("{}: Commit index set to {}", logName(), context.getCommitIndex());
270         }
271
272         // If commitIndex > lastApplied: increment lastApplied, apply
273         // log[lastApplied] to state machine (§5.3)
274         // check if there are any entries to be applied. last-applied can be equal to last-index
275         if (appendEntries.getLeaderCommit() > context.getLastApplied() &&
276             context.getLastApplied() < lastIndex) {
277             if(LOG.isDebugEnabled()) {
278                 LOG.debug("{}: applyLogToStateMachine, " +
279                         "appendEntries.getLeaderCommit(): {}," +
280                         "context.getLastApplied(): {}, lastIndex(): {}", logName(),
281                     appendEntries.getLeaderCommit(), context.getLastApplied(), lastIndex);
282             }
283
284             applyLogToStateMachine(appendEntries.getLeaderCommit());
285         }
286
287         AppendEntriesReply reply = new AppendEntriesReply(context.getId(), currentTerm(), true,
288             lastIndex, lastTerm(), context.getPayloadVersion());
289
290         if(LOG.isTraceEnabled()) {
291             LOG.trace("{}: handleAppendEntries returning : {}", logName(), reply);
292         } else if(LOG.isDebugEnabled() && numLogEntries > 0) {
293             LOG.debug("{}: handleAppendEntries returning : {}", logName(), reply);
294         }
295
296         sender.tell(reply, actor());
297
298         if (!context.getSnapshotManager().isCapturing()) {
299             super.performSnapshotWithoutCapture(appendEntries.getReplicatedToAllIndex());
300         }
301
302         return this;
303     }
304
305     private boolean isOutOfSync(AppendEntries appendEntries) {
306
307         long prevLogTerm = getLogEntryTerm(appendEntries.getPrevLogIndex());
308         boolean prevEntryPresent = isLogEntryPresent(appendEntries.getPrevLogIndex());
309         long lastIndex = lastIndex();
310         int numLogEntries = appendEntries.getEntries() != null ? appendEntries.getEntries().size() : 0;
311         boolean outOfSync = true;
312
313         if (lastIndex == -1 && appendEntries.getPrevLogIndex() != -1) {
314
315             // The follower's log is out of sync because the leader does have
316             // an entry at prevLogIndex and this follower has no entries in
317             // it's log.
318
319             LOG.debug("{}: The followers log is empty and the senders prevLogIndex is {}",
320                         logName(), appendEntries.getPrevLogIndex());
321         } else if (lastIndex > -1 && appendEntries.getPrevLogIndex() != -1 && !prevEntryPresent) {
322
323             // The follower's log is out of sync because the Leader's
324             // prevLogIndex entry was not found in it's log
325
326             LOG.debug("{}: The log is not empty but the prevLogIndex {} was not found in it - lastIndex: {}, snapshotIndex: {}",
327                         logName(), appendEntries.getPrevLogIndex(), lastIndex, context.getReplicatedLog().getSnapshotIndex());
328         } else if (lastIndex > -1 && prevEntryPresent && prevLogTerm != appendEntries.getPrevLogTerm()) {
329
330             // The follower's log is out of sync because the Leader's
331             // prevLogIndex entry does exist in the follower's log but it has
332             // a different term in it
333
334             LOG.debug("{}: The prevLogIndex {} was found in the log but the term {} is not equal to the append entries " +
335                       "prevLogTerm {} - lastIndex: {}, snapshotIndex: {}", logName(), appendEntries.getPrevLogIndex(),
336                       prevLogTerm, appendEntries.getPrevLogTerm(), lastIndex, context.getReplicatedLog().getSnapshotIndex());
337         } else if(appendEntries.getPrevLogIndex() == -1 && appendEntries.getPrevLogTerm() == -1
338                 && appendEntries.getReplicatedToAllIndex() != -1
339                 && !isLogEntryPresent(appendEntries.getReplicatedToAllIndex())) {
340             // This append entry comes from a leader who has it's log aggressively trimmed and so does not have
341             // the previous entry in it's in-memory journal
342
343             LOG.debug(
344                     "{}: Cannot append entries because the replicatedToAllIndex {} does not appear to be in the in-memory journal",
345                     logName(), appendEntries.getReplicatedToAllIndex());
346         } else if(appendEntries.getPrevLogIndex() == -1 && appendEntries.getPrevLogTerm() == -1
347                 && appendEntries.getReplicatedToAllIndex() != -1 && numLogEntries > 0
348                 && !isLogEntryPresent(appendEntries.getEntries().get(0).getIndex() - 1)) {
349             LOG.debug(
350                     "{}: Cannot append entries because the calculated previousIndex {} was not found in the in-memory journal",
351                     logName(), appendEntries.getEntries().get(0).getIndex() - 1);
352         } else {
353             outOfSync = false;
354         }
355         return outOfSync;
356     }
357
358     @Override
359     protected RaftActorBehavior handleAppendEntriesReply(ActorRef sender,
360         AppendEntriesReply appendEntriesReply) {
361         return this;
362     }
363
364     @Override
365     protected RaftActorBehavior handleRequestVoteReply(ActorRef sender,
366         RequestVoteReply requestVoteReply) {
367         return this;
368     }
369
370     @Override
371     public RaftActorBehavior handleMessage(ActorRef sender, Object message) {
372         if (message instanceof ElectionTimeout || message instanceof TimeoutNow) {
373             return handleElectionTimeout(message);
374         }
375
376         if (!(message instanceof RaftRPC)) {
377             // The rest of the processing requires the message to be a RaftRPC
378             return null;
379         }
380
381         final RaftRPC rpc = (RaftRPC) message;
382         // If RPC request or response contains term T > currentTerm:
383         // set currentTerm = T, convert to follower (§5.1)
384         // This applies to all RPC messages and responses
385         if (rpc.getTerm() > context.getTermInformation().getCurrentTerm()) {
386             LOG.debug("{}: Term {} in \"{}\" message is greater than follower's term {} - updating term",
387                 logName(), rpc.getTerm(), rpc, context.getTermInformation().getCurrentTerm());
388
389             context.getTermInformation().updateAndPersist(rpc.getTerm(), null);
390         }
391
392         if (rpc instanceof InstallSnapshot) {
393             handleInstallSnapshot(sender, (InstallSnapshot) rpc);
394             restartLastLeaderMessageTimer();
395             scheduleElection(electionDuration());
396             return this;
397         }
398
399         if (!(rpc instanceof RequestVote) || canGrantVote((RequestVote) rpc)) {
400             restartLastLeaderMessageTimer();
401             scheduleElection(electionDuration());
402         }
403
404         return super.handleMessage(sender, rpc);
405     }
406
407     private RaftActorBehavior handleElectionTimeout(Object message) {
408         // If the message is ElectionTimeout, verify we haven't actually seen a message from the leader
409         // during the election timeout interval. It may that the election timer expired b/c this actor
410         // was busy and messages got delayed, in which case leader messages would be backed up in the
411         // queue but would be processed before the ElectionTimeout message and thus would restart the
412         // lastLeaderMessageTimer.
413         long lastLeaderMessageInterval = lastLeaderMessageTimer.elapsed(TimeUnit.MILLISECONDS);
414         long electionTimeoutInMillis = context.getConfigParams().getElectionTimeOutInterval().toMillis();
415         boolean noLeaderMessageReceived = !lastLeaderMessageTimer.isRunning() ||
416                 lastLeaderMessageInterval >= electionTimeoutInMillis;
417
418         if(canStartElection()) {
419             if(message instanceof TimeoutNow) {
420                 LOG.debug("{}: Received TimeoutNow - switching to Candidate", logName());
421                 return internalSwitchBehavior(RaftState.Candidate);
422             } else if(noLeaderMessageReceived) {
423                 // Check the cluster state to see if the leader is known to be up before we go to Candidate.
424                 // However if we haven't heard from the leader in a long time even though the cluster state
425                 // indicates it's up then something is wrong - leader might be stuck indefinitely - so switch
426                 // to Candidate,
427                 long maxElectionTimeout = electionTimeoutInMillis * MAX_ELECTION_TIMEOUT_FACTOR;
428                 if(isLeaderAvailabilityKnown() && lastLeaderMessageInterval < maxElectionTimeout) {
429                     LOG.debug("{}: Received ElectionTimeout but leader appears to be available", logName());
430                     scheduleElection(electionDuration());
431                 } else {
432                     LOG.debug("{}: Received ElectionTimeout - switching to Candidate", logName());
433                     return internalSwitchBehavior(RaftState.Candidate);
434                 }
435             } else {
436                 LOG.debug("{}: Received ElectionTimeout but lastLeaderMessageInterval {} < election timeout {}",
437                         logName(), lastLeaderMessageInterval, context.getConfigParams().getElectionTimeOutInterval());
438                 scheduleElection(electionDuration());
439             }
440         } else if(message instanceof ElectionTimeout) {
441             if(noLeaderMessageReceived) {
442                 setLeaderId(null);
443             }
444
445             scheduleElection(electionDuration());
446         }
447
448         return this;
449     }
450
451     private boolean isLeaderAvailabilityKnown() {
452         if(leaderId == null) {
453             return false;
454         }
455
456         Optional<Cluster> cluster = context.getCluster();
457         if(!cluster.isPresent()) {
458             return false;
459         }
460
461         ActorSelection leaderActor = context.getPeerActorSelection(leaderId);
462         if(leaderActor == null) {
463             return false;
464         }
465
466         Address leaderAddress = leaderActor.anchorPath().address();
467
468         CurrentClusterState state = cluster.get().state();
469         Set<Member> unreachable = state.getUnreachable();
470
471         LOG.debug("{}: Checking for leader {} in the cluster unreachable set {}", logName(), leaderAddress,
472                 unreachable);
473
474         for(Member m: unreachable) {
475             if(leaderAddress.equals(m.address())) {
476                 LOG.info("{}: Leader {} is unreachable", logName(), leaderAddress);
477                 return false;
478             }
479         }
480
481         for(Member m: state.getMembers()) {
482             if(leaderAddress.equals(m.address())) {
483                 if(m.status() == MemberStatus.up() || m.status() == MemberStatus.weaklyUp()) {
484                     LOG.debug("{}: Leader {} cluster status is {} - leader is available", logName(),
485                             leaderAddress, m.status());
486                     return true;
487                 } else {
488                     LOG.debug("{}: Leader {} cluster status is {} - leader is unavailable", logName(),
489                             leaderAddress, m.status());
490                     return false;
491                 }
492             }
493         }
494
495         LOG.debug("{}: Leader {} not found in the cluster member set", logName(), leaderAddress);
496
497         return false;
498     }
499
500     private void handleInstallSnapshot(final ActorRef sender, InstallSnapshot installSnapshot) {
501
502         LOG.debug("{}: handleInstallSnapshot: {}", logName(), installSnapshot);
503
504         leaderId = installSnapshot.getLeaderId();
505
506         if(snapshotTracker == null){
507             snapshotTracker = new SnapshotTracker(LOG, installSnapshot.getTotalChunks(), installSnapshot.getLeaderId());
508         }
509
510         updateInitialSyncStatus(installSnapshot.getLastIncludedIndex(), installSnapshot.getLeaderId());
511
512         try {
513             final InstallSnapshotReply reply = new InstallSnapshotReply(
514                     currentTerm(), context.getId(), installSnapshot.getChunkIndex(), true);
515
516             if(snapshotTracker.addChunk(installSnapshot.getChunkIndex(), installSnapshot.getData(),
517                     installSnapshot.getLastChunkHashCode())){
518                 Snapshot snapshot = Snapshot.create(snapshotTracker.getSnapshot(),
519                         new ArrayList<ReplicatedLogEntry>(),
520                         installSnapshot.getLastIncludedIndex(),
521                         installSnapshot.getLastIncludedTerm(),
522                         installSnapshot.getLastIncludedIndex(),
523                         installSnapshot.getLastIncludedTerm(),
524                         context.getTermInformation().getCurrentTerm(),
525                         context.getTermInformation().getVotedFor(),
526                         installSnapshot.getServerConfig().orNull());
527
528                 ApplySnapshot.Callback applySnapshotCallback = new ApplySnapshot.Callback() {
529                     @Override
530                     public void onSuccess() {
531                         LOG.debug("{}: handleInstallSnapshot returning: {}", logName(), reply);
532
533                         sender.tell(reply, actor());
534                     }
535
536                     @Override
537                     public void onFailure() {
538                         sender.tell(new InstallSnapshotReply(currentTerm(), context.getId(), -1, false), actor());
539                     }
540                 };
541
542                 actor().tell(new ApplySnapshot(snapshot, applySnapshotCallback), actor());
543
544                 snapshotTracker = null;
545             } else {
546                 LOG.debug("{}: handleInstallSnapshot returning: {}", logName(), reply);
547
548                 sender.tell(reply, actor());
549             }
550         } catch (SnapshotTracker.InvalidChunkException e) {
551             LOG.debug("{}: Exception in InstallSnapshot of follower", logName(), e);
552
553             sender.tell(new InstallSnapshotReply(currentTerm(), context.getId(),
554                     -1, false), actor());
555             snapshotTracker = null;
556
557         } catch (Exception e){
558             LOG.error("{}: Exception in InstallSnapshot of follower", logName(), e);
559
560             //send reply with success as false. The chunk will be sent again on failure
561             sender.tell(new InstallSnapshotReply(currentTerm(), context.getId(),
562                     installSnapshot.getChunkIndex(), false), actor());
563
564         }
565     }
566
567     @Override
568     public void close() {
569         stopElection();
570     }
571
572     @VisibleForTesting
573     SnapshotTracker getSnapshotTracker(){
574         return snapshotTracker;
575     }
576 }

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