7ec9f2743c7b6472af4e6ccf521e7c5b4f030e02
[controller.git] / opendaylight / md-sal / sal-akka-raft / src / main / java / org / opendaylight / controller / cluster / raft / RaftActor.java
1 /*
2  * Copyright (c) 2014 Cisco Systems, Inc. and others.  All rights reserved.
3  * Copyright (c) 2015 Brocade Communications Systems, Inc. and others.  All rights reserved.
4  *
5  * This program and the accompanying materials are made available under the
6  * terms of the Eclipse Public License v1.0 which accompanies this distribution,
7  * and is available at http://www.eclipse.org/legal/epl-v10.html
8  */
9
10 package org.opendaylight.controller.cluster.raft;
11
12 import akka.actor.ActorRef;
13 import akka.actor.ActorSelection;
14 import akka.actor.PoisonPill;
15 import akka.actor.Status;
16 import com.google.common.annotations.VisibleForTesting;
17 import com.google.common.base.Optional;
18 import com.google.common.base.Preconditions;
19 import com.google.common.base.Verify;
20 import com.google.common.collect.Lists;
21 import java.util.Collection;
22 import java.util.HashMap;
23 import java.util.List;
24 import java.util.Map;
25 import java.util.Objects;
26 import java.util.concurrent.TimeUnit;
27 import javax.annotation.Nonnull;
28 import javax.annotation.Nullable;
29 import org.apache.commons.lang3.time.DurationFormatUtils;
30 import org.opendaylight.controller.cluster.DataPersistenceProvider;
31 import org.opendaylight.controller.cluster.DelegatingPersistentDataProvider;
32 import org.opendaylight.controller.cluster.NonPersistentDataProvider;
33 import org.opendaylight.controller.cluster.PersistentDataProvider;
34 import org.opendaylight.controller.cluster.common.actor.AbstractUntypedPersistentActor;
35 import org.opendaylight.controller.cluster.notifications.LeaderStateChanged;
36 import org.opendaylight.controller.cluster.notifications.RoleChanged;
37 import org.opendaylight.controller.cluster.raft.base.messages.ApplyState;
38 import org.opendaylight.controller.cluster.raft.base.messages.CheckConsensusReached;
39 import org.opendaylight.controller.cluster.raft.base.messages.InitiateCaptureSnapshot;
40 import org.opendaylight.controller.cluster.raft.base.messages.LeaderTransitioning;
41 import org.opendaylight.controller.cluster.raft.base.messages.Replicate;
42 import org.opendaylight.controller.cluster.raft.base.messages.SwitchBehavior;
43 import org.opendaylight.controller.cluster.raft.behaviors.AbstractLeader;
44 import org.opendaylight.controller.cluster.raft.behaviors.AbstractRaftActorBehavior;
45 import org.opendaylight.controller.cluster.raft.behaviors.Follower;
46 import org.opendaylight.controller.cluster.raft.behaviors.RaftActorBehavior;
47 import org.opendaylight.controller.cluster.raft.client.messages.FindLeader;
48 import org.opendaylight.controller.cluster.raft.client.messages.FindLeaderReply;
49 import org.opendaylight.controller.cluster.raft.client.messages.FollowerInfo;
50 import org.opendaylight.controller.cluster.raft.client.messages.GetOnDemandRaftState;
51 import org.opendaylight.controller.cluster.raft.client.messages.OnDemandRaftState;
52 import org.opendaylight.controller.cluster.raft.client.messages.Shutdown;
53 import org.opendaylight.controller.cluster.raft.messages.RequestLeadership;
54 import org.opendaylight.controller.cluster.raft.persisted.ApplyJournalEntries;
55 import org.opendaylight.controller.cluster.raft.persisted.NoopPayload;
56 import org.opendaylight.controller.cluster.raft.persisted.ServerConfigurationPayload;
57 import org.opendaylight.controller.cluster.raft.persisted.SimpleReplicatedLogEntry;
58 import org.opendaylight.controller.cluster.raft.protobuff.client.messages.Payload;
59 import org.opendaylight.yangtools.concepts.Identifier;
60 import org.opendaylight.yangtools.concepts.Immutable;
61
62 /**
63  * RaftActor encapsulates a state machine that needs to be kept synchronized
64  * in a cluster. It implements the RAFT algorithm as described in the paper
65  * <a href='https://ramcloud.stanford.edu/wiki/download/attachments/11370504/raft.pdf'>
66  * In Search of an Understandable Consensus Algorithm</a>
67  *
68  * <p>
69  * RaftActor has 3 states and each state has a certain behavior associated
70  * with it. A Raft actor can behave as,
71  * <ul>
72  * <li> A Leader </li>
73  * <li> A Follower (or) </li>
74  * <li> A Candidate </li>
75  * </ul>
76  *
77  * <p>
78  * A RaftActor MUST be a Leader in order to accept requests from clients to
79  * change the state of it's encapsulated state machine. Once a RaftActor becomes
80  * a Leader it is also responsible for ensuring that all followers ultimately
81  * have the same log and therefore the same state machine as itself.
82  *
83  * <p>
84  * The current behavior of a RaftActor determines how election for leadership
85  * is initiated and how peer RaftActors react to request for votes.
86  *
87  * <p>
88  * Each RaftActor also needs to know the current election term. It uses this
89  * information for a couple of things. One is to simply figure out who it
90  * voted for in the last election. Another is to figure out if the message
91  * it received to update it's state is stale.
92  *
93  * <p>
94  * The RaftActor uses akka-persistence to store it's replicated log.
95  * Furthermore through it's behaviors a Raft Actor determines
96  * <ul>
97  * <li> when a log entry should be persisted </li>
98  * <li> when a log entry should be applied to the state machine (and) </li>
99  * <li> when a snapshot should be saved </li>
100  * </ul>
101  */
102 public abstract class RaftActor extends AbstractUntypedPersistentActor {
103
104     private static final long APPLY_STATE_DELAY_THRESHOLD_IN_NANOS = TimeUnit.MILLISECONDS.toNanos(50L); // 50 millis
105
106     /**
107      * This context should NOT be passed directly to any other actor it is
108      * only to be consumed by the RaftActorBehaviors.
109      */
110     private final RaftActorContextImpl context;
111
112     private final DelegatingPersistentDataProvider delegatingPersistenceProvider;
113
114     private final PersistentDataProvider persistentProvider;
115
116     private final BehaviorStateTracker behaviorStateTracker = new BehaviorStateTracker();
117
118     private RaftActorRecoverySupport raftRecovery;
119
120     private RaftActorSnapshotMessageSupport snapshotSupport;
121
122     private RaftActorServerConfigurationSupport serverConfigurationSupport;
123
124     private boolean shuttingDown;
125
126     protected RaftActor(String id, Map<String, String> peerAddresses,
127          Optional<ConfigParams> configParams, short payloadVersion) {
128
129         persistentProvider = new PersistentDataProvider(this);
130         delegatingPersistenceProvider = new RaftActorDelegatingPersistentDataProvider(null, persistentProvider);
131
132         context = new RaftActorContextImpl(this.getSelf(),
133             this.getContext(), id, new ElectionTermImpl(persistentProvider, id, LOG),
134             -1, -1, peerAddresses,
135             configParams.isPresent() ? configParams.get() : new DefaultConfigParamsImpl(),
136             delegatingPersistenceProvider, this::handleApplyState, LOG);
137
138         context.setPayloadVersion(payloadVersion);
139         context.setReplicatedLog(ReplicatedLogImpl.newInstance(context));
140     }
141
142     @Override
143     public void preStart() throws Exception {
144         LOG.info("Starting recovery for {} with journal batch size {}", persistenceId(),
145                 context.getConfigParams().getJournalRecoveryLogBatchSize());
146
147         super.preStart();
148
149         snapshotSupport = newRaftActorSnapshotMessageSupport();
150         serverConfigurationSupport = new RaftActorServerConfigurationSupport(this);
151     }
152
153     @Override
154     public void postStop() {
155         context.close();
156         super.postStop();
157     }
158
159     @Override
160     protected void handleRecover(Object message) {
161         if (raftRecovery == null) {
162             raftRecovery = newRaftActorRecoverySupport();
163         }
164
165         boolean recoveryComplete = raftRecovery.handleRecoveryMessage(message, persistentProvider);
166         if (recoveryComplete) {
167             onRecoveryComplete();
168
169             initializeBehavior();
170
171             raftRecovery = null;
172         }
173     }
174
175     protected RaftActorRecoverySupport newRaftActorRecoverySupport() {
176         return new RaftActorRecoverySupport(context, getRaftActorRecoveryCohort());
177     }
178
179     @VisibleForTesting
180     void initializeBehavior() {
181         changeCurrentBehavior(new Follower(context));
182     }
183
184     @VisibleForTesting
185     @SuppressWarnings("checkstyle:IllegalCatch")
186     protected void changeCurrentBehavior(RaftActorBehavior newBehavior) {
187         final RaftActorBehavior currentBehavior = getCurrentBehavior();
188         if (currentBehavior != null) {
189             try {
190                 currentBehavior.close();
191             } catch (Exception e) {
192                 LOG.warn("{}: Error closing behavior {}", persistence(), currentBehavior, e);
193             }
194         }
195
196         final BehaviorState state = behaviorStateTracker.capture(currentBehavior);
197         setCurrentBehavior(newBehavior);
198         handleBehaviorChange(state, newBehavior);
199     }
200
201     /**
202      * Method exposed for subclasses to plug-in their logic. This method is invoked by {@link #handleCommand(Object)}
203      * for messages which are not handled by this class. Subclasses overriding this class should fall back to this
204      * implementation for messages which they do not handle
205      *
206      * @param message Incoming command message
207      */
208     protected void handleNonRaftCommand(final Object message) {
209         unhandled(message);
210     }
211
212     /**
213      * Handles a message.
214      *
215      * @deprecated This method is not final for testing purposes. DO NOT OVERRIDE IT, override
216      * {@link #handleNonRaftCommand(Object)} instead.
217      */
218     @Deprecated
219     @Override
220     // FIXME: make this method final once our unit tests do not need to override it
221     protected void handleCommand(final Object message) {
222         if (serverConfigurationSupport.handleMessage(message, getSender())) {
223             return;
224         }
225         if (snapshotSupport.handleSnapshotMessage(message, getSender())) {
226             return;
227         }
228         if (message instanceof ApplyState) {
229             ApplyState applyState = (ApplyState) message;
230
231             if (!hasFollowers()) {
232                 // for single node, the capture should happen after the apply state
233                 // as we delete messages from the persistent journal which have made it to the snapshot
234                 // capturing the snapshot before applying makes the persistent journal and snapshot out of sync
235                 // and recovery shows data missing
236                 context.getReplicatedLog().captureSnapshotIfReady(applyState.getReplicatedLogEntry());
237
238                 context.getSnapshotManager().trimLog(context.getLastApplied());
239             }
240
241             possiblyHandleBehaviorMessage(message);
242         } else if (message instanceof ApplyJournalEntries) {
243             ApplyJournalEntries applyEntries = (ApplyJournalEntries) message;
244             LOG.debug("{}: Persisting ApplyJournalEntries with index={}", persistenceId(), applyEntries.getToIndex());
245
246             persistence().persistAsync(applyEntries, NoopProcedure.instance());
247
248         } else if (message instanceof FindLeader) {
249             getSender().tell(
250                 new FindLeaderReply(getLeaderAddress()),
251                 getSelf()
252             );
253         } else if (message instanceof GetOnDemandRaftState) {
254             onGetOnDemandRaftStats();
255         } else if (message instanceof InitiateCaptureSnapshot) {
256             captureSnapshot();
257         } else if (message instanceof SwitchBehavior) {
258             switchBehavior((SwitchBehavior) message);
259         } else if (message instanceof LeaderTransitioning) {
260             onLeaderTransitioning((LeaderTransitioning)message);
261         } else if (message instanceof Shutdown) {
262             onShutDown();
263         } else if (message instanceof Runnable) {
264             ((Runnable)message).run();
265         } else if (message instanceof NoopPayload) {
266             persistData(null, null, (NoopPayload) message, false);
267         } else if (message instanceof RequestLeadership) {
268             onRequestLeadership((RequestLeadership) message);
269         } else if (!possiblyHandleBehaviorMessage(message)) {
270             handleNonRaftCommand(message);
271         }
272     }
273
274     private void onRequestLeadership(final RequestLeadership message) {
275         LOG.debug("{}: onRequestLeadership {}", persistenceId(), message);
276         if (!isLeader()) {
277             // non-leader cannot satisfy leadership request
278             LOG.warn("{}: onRequestLeadership {} was sent to non-leader."
279                     + " Current behavior: {}. Sending failure response",
280                     persistenceId(), getCurrentBehavior().state());
281             message.getReplyTo().tell(new LeadershipTransferFailedException("Cannot transfer leader to "
282                     + message.getRequestedFollowerId()
283                     + ". RequestLeadership message was sent to non-leader " + persistenceId()), getSelf());
284             return;
285         }
286
287         final String requestedFollowerId = message.getRequestedFollowerId();
288         final ActorRef replyTo = message.getReplyTo();
289         initiateLeadershipTransfer(new RaftActorLeadershipTransferCohort.OnComplete() {
290             @Override
291             public void onSuccess(final ActorRef raftActorRef) {
292                 // sanity check
293                 if (!requestedFollowerId.equals(getLeaderId())) {
294                     onFailure(raftActorRef);
295                 }
296
297                 LOG.debug("{}: Leadership transferred successfully to {}", persistenceId(), requestedFollowerId);
298                 replyTo.tell(new Status.Success(null), getSelf());
299             }
300
301             @Override
302             public void onFailure(final ActorRef raftActorRef) {
303                 LOG.debug("{}: LeadershipTransfer request from {} failed", persistenceId(), requestedFollowerId);
304                 replyTo.tell(new Status.Failure(
305                         new LeadershipTransferFailedException(
306                                 "Failed to transfer leadership to " + requestedFollowerId
307                                         + ". Follower is not ready to become leader")),
308                         getSelf());
309             }
310         }, message.getRequestedFollowerId(), RaftActorLeadershipTransferCohort.USE_DEFAULT_LEADER_TIMEOUT);
311     }
312
313     private boolean possiblyHandleBehaviorMessage(final Object message) {
314         final RaftActorBehavior currentBehavior = getCurrentBehavior();
315         final BehaviorState state = behaviorStateTracker.capture(currentBehavior);
316
317         // A behavior indicates that it processed the change by returning a reference to the next behavior
318         // to be used. A null return indicates it has not processed the message and we should be passing it to
319         // the subclass for handling.
320         final RaftActorBehavior nextBehavior = currentBehavior.handleMessage(getSender(), message);
321         if (nextBehavior != null) {
322             switchBehavior(state, nextBehavior);
323             return true;
324         }
325
326         return false;
327     }
328
329     private void initiateLeadershipTransfer(final RaftActorLeadershipTransferCohort.OnComplete onComplete,
330             @Nullable final String followerId, long newLeaderTimeoutInMillis) {
331         LOG.debug("{}: Initiating leader transfer", persistenceId());
332
333         RaftActorLeadershipTransferCohort leadershipTransferInProgress = context.getRaftActorLeadershipTransferCohort();
334         if (leadershipTransferInProgress == null) {
335             leadershipTransferInProgress = new RaftActorLeadershipTransferCohort(this, followerId);
336             leadershipTransferInProgress.setNewLeaderTimeoutInMillis(newLeaderTimeoutInMillis);
337             leadershipTransferInProgress.addOnComplete(new RaftActorLeadershipTransferCohort.OnComplete() {
338                 @Override
339                 public void onSuccess(ActorRef raftActorRef) {
340                     context.setRaftActorLeadershipTransferCohort(null);
341                 }
342
343                 @Override
344                 public void onFailure(ActorRef raftActorRef) {
345                     context.setRaftActorLeadershipTransferCohort(null);
346                 }
347             });
348
349             leadershipTransferInProgress.addOnComplete(onComplete);
350
351             context.setRaftActorLeadershipTransferCohort(leadershipTransferInProgress);
352             leadershipTransferInProgress.init();
353
354         } else {
355             LOG.debug("{}: prior leader transfer in progress - adding callback", persistenceId());
356             leadershipTransferInProgress.addOnComplete(onComplete);
357         }
358     }
359
360     private void onShutDown() {
361         LOG.debug("{}: onShutDown", persistenceId());
362
363         if (shuttingDown) {
364             return;
365         }
366
367         shuttingDown = true;
368
369         final RaftActorBehavior currentBehavior = context.getCurrentBehavior();
370         switch (currentBehavior.state()) {
371             case Leader:
372             case PreLeader:
373                 // Fall-through to more work
374                 break;
375             default:
376                 // For non-leaders shutdown is a no-op
377                 self().tell(PoisonPill.getInstance(), self());
378                 return;
379         }
380
381         if (context.hasFollowers()) {
382             initiateLeadershipTransfer(new RaftActorLeadershipTransferCohort.OnComplete() {
383                 @Override
384                 public void onSuccess(ActorRef raftActorRef) {
385                     LOG.debug("{}: leader transfer succeeded - sending PoisonPill", persistenceId());
386                     raftActorRef.tell(PoisonPill.getInstance(), raftActorRef);
387                 }
388
389                 @Override
390                 public void onFailure(ActorRef raftActorRef) {
391                     LOG.debug("{}: leader transfer failed - sending PoisonPill", persistenceId());
392                     raftActorRef.tell(PoisonPill.getInstance(), raftActorRef);
393                 }
394             }, null, TimeUnit.MILLISECONDS.convert(2, TimeUnit.SECONDS));
395         } else {
396             pauseLeader(new TimedRunnable(context.getConfigParams().getElectionTimeOutInterval(), this) {
397                 @Override
398                 protected void doRun() {
399                     self().tell(PoisonPill.getInstance(), self());
400                 }
401
402                 @Override
403                 protected void doCancel() {
404                     self().tell(PoisonPill.getInstance(), self());
405                 }
406             });
407         }
408     }
409
410     private void onLeaderTransitioning(final LeaderTransitioning leaderTransitioning) {
411         LOG.debug("{}: onLeaderTransitioning: {}", persistenceId(), leaderTransitioning);
412         Optional<ActorRef> roleChangeNotifier = getRoleChangeNotifier();
413         if (getRaftState() == RaftState.Follower && roleChangeNotifier.isPresent()
414                 && leaderTransitioning.getLeaderId().equals(getCurrentBehavior().getLeaderId())) {
415             roleChangeNotifier.get().tell(newLeaderStateChanged(getId(), null,
416                 getCurrentBehavior().getLeaderPayloadVersion()), getSelf());
417         }
418     }
419
420     private void switchBehavior(SwitchBehavior message) {
421         if (!getRaftActorContext().getRaftPolicy().automaticElectionsEnabled()) {
422             RaftState newState = message.getNewState();
423             if (newState == RaftState.Leader || newState == RaftState.Follower) {
424                 switchBehavior(behaviorStateTracker.capture(getCurrentBehavior()),
425                     AbstractRaftActorBehavior.createBehavior(context, message.getNewState()));
426                 getRaftActorContext().getTermInformation().updateAndPersist(message.getNewTerm(), "");
427             } else {
428                 LOG.warn("Switching to behavior : {} - not supported", newState);
429             }
430         }
431     }
432
433     private void switchBehavior(final BehaviorState oldBehaviorState, final RaftActorBehavior nextBehavior) {
434         setCurrentBehavior(nextBehavior);
435         handleBehaviorChange(oldBehaviorState, nextBehavior);
436     }
437
438     @VisibleForTesting
439     RaftActorSnapshotMessageSupport newRaftActorSnapshotMessageSupport() {
440         return new RaftActorSnapshotMessageSupport(context, getRaftActorSnapshotCohort());
441     }
442
443     private void onGetOnDemandRaftStats() {
444         // Debugging message to retrieve raft stats.
445
446         Map<String, String> peerAddresses = new HashMap<>();
447         Map<String, Boolean> peerVotingStates = new HashMap<>();
448         for (PeerInfo info: context.getPeers()) {
449             peerVotingStates.put(info.getId(), info.isVoting());
450             peerAddresses.put(info.getId(), info.getAddress() != null ? info.getAddress() : "");
451         }
452
453         final RaftActorBehavior currentBehavior = context.getCurrentBehavior();
454         OnDemandRaftState.AbstractBuilder<?> builder = newOnDemandRaftStateBuilder()
455                 .commitIndex(context.getCommitIndex())
456                 .currentTerm(context.getTermInformation().getCurrentTerm())
457                 .inMemoryJournalDataSize(replicatedLog().dataSize())
458                 .inMemoryJournalLogSize(replicatedLog().size())
459                 .isSnapshotCaptureInitiated(context.getSnapshotManager().isCapturing())
460                 .lastApplied(context.getLastApplied())
461                 .lastIndex(replicatedLog().lastIndex())
462                 .lastTerm(replicatedLog().lastTerm())
463                 .leader(getLeaderId())
464                 .raftState(currentBehavior.state().toString())
465                 .replicatedToAllIndex(currentBehavior.getReplicatedToAllIndex())
466                 .snapshotIndex(replicatedLog().getSnapshotIndex())
467                 .snapshotTerm(replicatedLog().getSnapshotTerm())
468                 .votedFor(context.getTermInformation().getVotedFor())
469                 .isVoting(context.isVotingMember())
470                 .peerAddresses(peerAddresses)
471                 .peerVotingStates(peerVotingStates)
472                 .customRaftPolicyClassName(context.getConfigParams().getCustomRaftPolicyImplementationClass());
473
474         ReplicatedLogEntry lastLogEntry = replicatedLog().last();
475         if (lastLogEntry != null) {
476             builder.lastLogIndex(lastLogEntry.getIndex());
477             builder.lastLogTerm(lastLogEntry.getTerm());
478         }
479
480         if (getCurrentBehavior() instanceof AbstractLeader) {
481             AbstractLeader leader = (AbstractLeader)getCurrentBehavior();
482             Collection<String> followerIds = leader.getFollowerIds();
483             List<FollowerInfo> followerInfoList = Lists.newArrayListWithCapacity(followerIds.size());
484             for (String id: followerIds) {
485                 final FollowerLogInformation info = leader.getFollower(id);
486                 followerInfoList.add(new FollowerInfo(id, info.getNextIndex(), info.getMatchIndex(),
487                         info.isFollowerActive(), DurationFormatUtils.formatDurationHMS(info.timeSinceLastActivity()),
488                         context.getPeerInfo(info.getId()).isVoting()));
489             }
490
491             builder.followerInfoList(followerInfoList);
492         }
493
494         sender().tell(builder.build(), self());
495
496     }
497
498     protected OnDemandRaftState.AbstractBuilder<?> newOnDemandRaftStateBuilder() {
499         return OnDemandRaftState.builder();
500     }
501
502     private void handleBehaviorChange(BehaviorState oldBehaviorState, RaftActorBehavior currentBehavior) {
503         RaftActorBehavior oldBehavior = oldBehaviorState.getBehavior();
504
505         if (oldBehavior != currentBehavior) {
506             onStateChanged();
507         }
508
509         String lastLeaderId = oldBehavior == null ? null : oldBehaviorState.getLastLeaderId();
510         String lastValidLeaderId = oldBehavior == null ? null : oldBehaviorState.getLastValidLeaderId();
511         String oldBehaviorStateName = oldBehavior == null ? null : oldBehavior.state().name();
512
513         // it can happen that the state has not changed but the leader has changed.
514         Optional<ActorRef> roleChangeNotifier = getRoleChangeNotifier();
515         if (!Objects.equals(lastLeaderId, currentBehavior.getLeaderId())
516                 || oldBehaviorState.getLeaderPayloadVersion() != currentBehavior.getLeaderPayloadVersion()) {
517             if (roleChangeNotifier.isPresent()) {
518                 roleChangeNotifier.get().tell(newLeaderStateChanged(getId(), currentBehavior.getLeaderId(),
519                         currentBehavior.getLeaderPayloadVersion()), getSelf());
520             }
521
522             onLeaderChanged(lastValidLeaderId, currentBehavior.getLeaderId());
523
524             RaftActorLeadershipTransferCohort leadershipTransferInProgress =
525                     context.getRaftActorLeadershipTransferCohort();
526             if (leadershipTransferInProgress != null) {
527                 leadershipTransferInProgress.onNewLeader(currentBehavior.getLeaderId());
528             }
529
530             serverConfigurationSupport.onNewLeader(currentBehavior.getLeaderId());
531         }
532
533         if (roleChangeNotifier.isPresent()
534                 && (oldBehavior == null || oldBehavior.state() != currentBehavior.state())) {
535             roleChangeNotifier.get().tell(new RoleChanged(getId(), oldBehaviorStateName ,
536                     currentBehavior.state().name()), getSelf());
537         }
538     }
539
540     private void handleApplyState(ApplyState applyState) {
541         long startTime = System.nanoTime();
542
543         Payload payload = applyState.getReplicatedLogEntry().getData();
544         if (LOG.isDebugEnabled()) {
545             LOG.debug("{}: Applying state for log index {} data {}",
546                 persistenceId(), applyState.getReplicatedLogEntry().getIndex(), payload);
547         }
548
549         if (!(payload instanceof NoopPayload) && !(payload instanceof ServerConfigurationPayload)) {
550             applyState(applyState.getClientActor(), applyState.getIdentifier(), payload);
551         }
552
553         long elapsedTime = System.nanoTime() - startTime;
554         if (elapsedTime >= APPLY_STATE_DELAY_THRESHOLD_IN_NANOS) {
555             LOG.debug("ApplyState took more time than expected. Elapsed Time = {} ms ApplyState = {}",
556                     TimeUnit.NANOSECONDS.toMillis(elapsedTime), applyState);
557         }
558
559         // Send the ApplyState message back to self to handle further processing asynchronously.
560         self().tell(applyState, self());
561     }
562
563     protected LeaderStateChanged newLeaderStateChanged(String memberId, String leaderId, short leaderPayloadVersion) {
564         return new LeaderStateChanged(memberId, leaderId, leaderPayloadVersion);
565     }
566
567     @Override
568     public long snapshotSequenceNr() {
569         // When we do a snapshot capture, we also capture and save the sequence-number of the persistent journal,
570         // so that we can delete the persistent journal based on the saved sequence-number
571         // However , when akka replays the journal during recovery, it replays it from the sequence number when the
572         // snapshot was saved and not the number we saved. We would want to override it , by asking akka to use the
573         // last-sequence number known to us.
574         return context.getSnapshotManager().getLastSequenceNumber();
575     }
576
577     /**
578      * Persists the given Payload in the journal and replicates to any followers. After successful completion,
579      * {@link #applyState(ActorRef, Identifier, Object)} is notified.
580      *
581      * @param clientActor optional ActorRef that is provided via the applyState callback
582      * @param identifier the payload identifier
583      * @param data the payload data to persist
584      * @param batchHint if true, an attempt is made to delay immediate replication and batch the payload with
585      *        subsequent payloads for efficiency. Otherwise the payload is immediately replicated.
586      */
587     protected final void persistData(final ActorRef clientActor, final Identifier identifier, final Payload data,
588             final boolean batchHint) {
589         ReplicatedLogEntry replicatedLogEntry = new SimpleReplicatedLogEntry(
590             context.getReplicatedLog().lastIndex() + 1,
591             context.getTermInformation().getCurrentTerm(), data);
592         replicatedLogEntry.setPersistencePending(true);
593
594         LOG.debug("{}: Persist data {}", persistenceId(), replicatedLogEntry);
595
596         final RaftActorContext raftContext = getRaftActorContext();
597
598         boolean wasAppended = replicatedLog().appendAndPersist(replicatedLogEntry, persistedLogEntry -> {
599             // Clear the persistence pending flag in the log entry.
600             persistedLogEntry.setPersistencePending(false);
601
602             if (!hasFollowers()) {
603                 // Increment the Commit Index and the Last Applied values
604                 raftContext.setCommitIndex(persistedLogEntry.getIndex());
605                 raftContext.setLastApplied(persistedLogEntry.getIndex());
606
607                 // Apply the state immediately.
608                 handleApplyState(new ApplyState(clientActor, identifier, persistedLogEntry));
609
610                 // Send a ApplyJournalEntries message so that we write the fact that we applied
611                 // the state to durable storage
612                 self().tell(new ApplyJournalEntries(persistedLogEntry.getIndex()), self());
613
614             } else {
615                 context.getReplicatedLog().captureSnapshotIfReady(replicatedLogEntry);
616
617                 // Local persistence is complete so send the CheckConsensusReached message to the behavior (which
618                 // normally should still be the leader) to check if consensus has now been reached in conjunction with
619                 // follower replication.
620                 getCurrentBehavior().handleMessage(getSelf(), CheckConsensusReached.INSTANCE);
621             }
622         }, true);
623
624         if (wasAppended && hasFollowers()) {
625             // Send log entry for replication.
626             getCurrentBehavior().handleMessage(getSelf(), new Replicate(clientActor, identifier, replicatedLogEntry,
627                     !batchHint));
628         }
629     }
630
631     private ReplicatedLog replicatedLog() {
632         return context.getReplicatedLog();
633     }
634
635     protected String getId() {
636         return context.getId();
637     }
638
639     @VisibleForTesting
640     void setCurrentBehavior(RaftActorBehavior behavior) {
641         context.setCurrentBehavior(behavior);
642     }
643
644     protected RaftActorBehavior getCurrentBehavior() {
645         return context.getCurrentBehavior();
646     }
647
648     /**
649      * Derived actors can call the isLeader method to check if the current
650      * RaftActor is the Leader or not.
651      *
652      * @return true it this RaftActor is a Leader false otherwise
653      */
654     protected boolean isLeader() {
655         return context.getId().equals(getCurrentBehavior().getLeaderId());
656     }
657
658     protected final boolean isLeaderActive() {
659         return getRaftState() != RaftState.IsolatedLeader && getRaftState() != RaftState.PreLeader
660                 && !shuttingDown && !isLeadershipTransferInProgress();
661     }
662
663     protected boolean isLeadershipTransferInProgress() {
664         RaftActorLeadershipTransferCohort leadershipTransferInProgress = context.getRaftActorLeadershipTransferCohort();
665         return leadershipTransferInProgress != null && leadershipTransferInProgress.isTransferring();
666     }
667
668     /**
669      * Derived actor can call getLeader if they need a reference to the Leader.
670      * This would be useful for example in forwarding a request to an actor
671      * which is the leader
672      *
673      * @return A reference to the leader if known, null otherwise
674      */
675     public ActorSelection getLeader() {
676         String leaderAddress = getLeaderAddress();
677
678         if (leaderAddress == null) {
679             return null;
680         }
681
682         return context.actorSelection(leaderAddress);
683     }
684
685     /**
686      * Returns the id of the current leader.
687      *
688      * @return the current leader's id
689      */
690     protected final String getLeaderId() {
691         return getCurrentBehavior().getLeaderId();
692     }
693
694     @VisibleForTesting
695     protected final RaftState getRaftState() {
696         return getCurrentBehavior().state();
697     }
698
699     protected Long getCurrentTerm() {
700         return context.getTermInformation().getCurrentTerm();
701     }
702
703     protected RaftActorContext getRaftActorContext() {
704         return context;
705     }
706
707     protected void updateConfigParams(ConfigParams configParams) {
708
709         // obtain the RaftPolicy for oldConfigParams and the updated one.
710         String oldRaftPolicy = context.getConfigParams().getCustomRaftPolicyImplementationClass();
711         String newRaftPolicy = configParams.getCustomRaftPolicyImplementationClass();
712
713         LOG.debug("{}: RaftPolicy used with prev.config {}, RaftPolicy used with newConfig {}", persistenceId(),
714             oldRaftPolicy, newRaftPolicy);
715         context.setConfigParams(configParams);
716         if (!Objects.equals(oldRaftPolicy, newRaftPolicy)) {
717             // The RaftPolicy was modified. If the current behavior is Follower then re-initialize to Follower
718             // but transfer the previous leaderId so it doesn't immediately try to schedule an election. This
719             // avoids potential disruption. Otherwise, switch to Follower normally.
720             RaftActorBehavior behavior = getCurrentBehavior();
721             if (behavior != null && behavior.state() == RaftState.Follower) {
722                 String previousLeaderId = behavior.getLeaderId();
723                 short previousLeaderPayloadVersion = behavior.getLeaderPayloadVersion();
724
725                 LOG.debug("{}: Re-initializing to Follower with previous leaderId {}", persistenceId(),
726                         previousLeaderId);
727
728                 changeCurrentBehavior(new Follower(context, previousLeaderId, previousLeaderPayloadVersion));
729             } else {
730                 initializeBehavior();
731             }
732         }
733     }
734
735     public final DataPersistenceProvider persistence() {
736         return delegatingPersistenceProvider.getDelegate();
737     }
738
739     public void setPersistence(DataPersistenceProvider provider) {
740         delegatingPersistenceProvider.setDelegate(provider);
741     }
742
743     protected void setPersistence(boolean persistent) {
744         DataPersistenceProvider currentPersistence = persistence();
745         if (persistent && (currentPersistence == null || !currentPersistence.isRecoveryApplicable())) {
746             setPersistence(new PersistentDataProvider(this));
747
748             if (getCurrentBehavior() != null) {
749                 LOG.info("{}: Persistence has been enabled - capturing snapshot", persistenceId());
750                 captureSnapshot();
751             }
752         } else if (!persistent && (currentPersistence == null || currentPersistence.isRecoveryApplicable())) {
753             setPersistence(new NonPersistentDataProvider() {
754                 /**
755                  * The way snapshotting works is,
756                  * <ol>
757                  * <li> RaftActor calls createSnapshot on the Shard
758                  * <li> Shard sends a CaptureSnapshotReply and RaftActor then calls saveSnapshot
759                  * <li> When saveSnapshot is invoked on the akka-persistence API it uses the SnapshotStore to save
760                  * the snapshot. The SnapshotStore sends SaveSnapshotSuccess or SaveSnapshotFailure. When the
761                  * RaftActor gets SaveSnapshot success it commits the snapshot to the in-memory journal. This
762                  * commitSnapshot is mimicking what is done in SaveSnapshotSuccess.
763                  * </ol>
764                  */
765                 @Override
766                 public void saveSnapshot(Object object) {
767                     // Make saving Snapshot successful
768                     // Committing the snapshot here would end up calling commit in the creating state which would
769                     // be a state violation. That's why now we send a message to commit the snapshot.
770                     self().tell(RaftActorSnapshotMessageSupport.COMMIT_SNAPSHOT, self());
771                 }
772             });
773         }
774     }
775
776     /**
777      * setPeerAddress sets the address of a known peer at a later time.
778      *
779      * <p>
780      * This is to account for situations where a we know that a peer
781      * exists but we do not know an address up-front. This may also be used in
782      * situations where a known peer starts off in a different location and we
783      * need to change it's address
784      *
785      * <p>
786      * Note that if the peerId does not match the list of peers passed to
787      * this actor during construction an IllegalStateException will be thrown.
788      */
789     protected void setPeerAddress(String peerId, String peerAddress) {
790         context.setPeerAddress(peerId, peerAddress);
791     }
792
793     /**
794      * The applyState method will be called by the RaftActor when some data
795      * needs to be applied to the actor's state.
796      *
797      * @param clientActor A reference to the client who sent this message. This
798      *                    is the same reference that was passed to persistData
799      *                    by the derived actor. clientActor may be null when
800      *                    the RaftActor is behaving as a follower or during
801      *                    recovery.
802      * @param identifier  The identifier of the persisted data. This is also
803      *                    the same identifier that was passed to persistData by
804      *                    the derived actor. identifier may be null when
805      *                    the RaftActor is behaving as a follower or during
806      *                    recovery
807      * @param data        A piece of data that was persisted by the persistData call.
808      *                    This should NEVER be null.
809      */
810     protected abstract void applyState(ActorRef clientActor, Identifier identifier, Object data);
811
812     /**
813      * Returns the RaftActorRecoveryCohort to participate in persistence recovery.
814      */
815     @Nonnull
816     protected abstract RaftActorRecoveryCohort getRaftActorRecoveryCohort();
817
818     /**
819      * This method is called when recovery is complete.
820      */
821     protected abstract void onRecoveryComplete();
822
823     /**
824      * Returns the RaftActorSnapshotCohort to participate in snapshot captures.
825      */
826     @Nonnull
827     protected abstract RaftActorSnapshotCohort getRaftActorSnapshotCohort();
828
829     /**
830      * This method will be called by the RaftActor when the state of the
831      * RaftActor changes. The derived actor can then use methods like
832      * isLeader or getLeader to do something useful
833      */
834     protected abstract void onStateChanged();
835
836     /**
837      * Notifier Actor for this RaftActor to notify when a role change happens.
838      *
839      * @return ActorRef - ActorRef of the notifier or Optional.absent if none.
840      */
841     protected abstract Optional<ActorRef> getRoleChangeNotifier();
842
843     /**
844      * This method is called prior to operations such as leadership transfer and actor shutdown when the leader
845      * must pause or stop its duties. This method allows derived classes to gracefully pause or finish current
846      * work prior to performing the operation. On completion of any work, the run method must be called on the
847      * given Runnable to proceed with the given operation. <b>Important:</b> the run method must be called on
848      * this actor's thread dispatcher as as it modifies internal state.
849      *
850      * <p>
851      * The default implementation immediately runs the operation.
852      *
853      * @param operation the operation to run
854      */
855     protected void pauseLeader(Runnable operation) {
856         operation.run();
857     }
858
859     protected void onLeaderChanged(String oldLeader, String newLeader) {
860     }
861
862     private String getLeaderAddress() {
863         if (isLeader()) {
864             return getSelf().path().toString();
865         }
866         String leaderId = getLeaderId();
867         if (leaderId == null) {
868             return null;
869         }
870         String peerAddress = context.getPeerAddress(leaderId);
871         LOG.debug("{}: getLeaderAddress leaderId = {} peerAddress = {}", persistenceId(), leaderId, peerAddress);
872
873         return peerAddress;
874     }
875
876     protected boolean hasFollowers() {
877         return getRaftActorContext().hasFollowers();
878     }
879
880     private void captureSnapshot() {
881         SnapshotManager snapshotManager = context.getSnapshotManager();
882
883         if (!snapshotManager.isCapturing()) {
884             final long idx = getCurrentBehavior().getReplicatedToAllIndex();
885             LOG.debug("Take a snapshot of current state. lastReplicatedLog is {} and replicatedToAllIndex is {}",
886                 replicatedLog().last(), idx);
887
888             snapshotManager.capture(replicatedLog().last(), idx);
889         }
890     }
891
892     /**
893      * Switch this member to non-voting status. This is a no-op for all behaviors except when we are the leader,
894      * in which case we need to step down.
895      */
896     void becomeNonVoting() {
897         if (isLeader()) {
898             initiateLeadershipTransfer(new RaftActorLeadershipTransferCohort.OnComplete() {
899                 @Override
900                 public void onSuccess(ActorRef raftActorRef) {
901                     LOG.debug("{}: leader transfer succeeded after change to non-voting", persistenceId());
902                     ensureFollowerState();
903                 }
904
905                 @Override
906                 public void onFailure(ActorRef raftActorRef) {
907                     LOG.debug("{}: leader transfer failed after change to non-voting", persistenceId());
908                     ensureFollowerState();
909                 }
910
911                 private void ensureFollowerState() {
912                     // Whether or not leadership transfer succeeded, we have to step down as leader and
913                     // switch to Follower so ensure that.
914                     if (getRaftState() != RaftState.Follower) {
915                         initializeBehavior();
916                     }
917                 }
918             }, null, RaftActorLeadershipTransferCohort.USE_DEFAULT_LEADER_TIMEOUT);
919         }
920     }
921
922     /**
923      * A point-in-time capture of {@link RaftActorBehavior} state critical for transitioning between behaviors.
924      */
925     private abstract static class BehaviorState implements Immutable {
926         @Nullable abstract RaftActorBehavior getBehavior();
927
928         @Nullable abstract String getLastValidLeaderId();
929
930         @Nullable abstract String getLastLeaderId();
931
932         @Nullable abstract short getLeaderPayloadVersion();
933     }
934
935     /**
936      * A {@link BehaviorState} corresponding to non-null {@link RaftActorBehavior} state.
937      */
938     private static final class SimpleBehaviorState extends BehaviorState {
939         private final RaftActorBehavior behavior;
940         private final String lastValidLeaderId;
941         private final String lastLeaderId;
942         private final short leaderPayloadVersion;
943
944         SimpleBehaviorState(final String lastValidLeaderId, final String lastLeaderId,
945                 final RaftActorBehavior behavior) {
946             this.lastValidLeaderId = lastValidLeaderId;
947             this.lastLeaderId = lastLeaderId;
948             this.behavior = Preconditions.checkNotNull(behavior);
949             this.leaderPayloadVersion = behavior.getLeaderPayloadVersion();
950         }
951
952         @Override
953         RaftActorBehavior getBehavior() {
954             return behavior;
955         }
956
957         @Override
958         String getLastValidLeaderId() {
959             return lastValidLeaderId;
960         }
961
962         @Override
963         short getLeaderPayloadVersion() {
964             return leaderPayloadVersion;
965         }
966
967         @Override
968         String getLastLeaderId() {
969             return lastLeaderId;
970         }
971     }
972
973     /**
974      * Class tracking behavior-related information, which we need to keep around and pass across behavior switches.
975      * An instance is created for each RaftActor. It has two functions:
976      * - it keeps track of the last leader ID we have encountered since we have been created
977      * - it creates state capture needed to transition from one behavior to the next
978      */
979     private static final class BehaviorStateTracker {
980         /**
981          * A {@link BehaviorState} corresponding to null {@link RaftActorBehavior} state. Since null behavior is only
982          * allowed before we receive the first message, we know the leader ID to be null.
983          */
984         private static final BehaviorState NULL_BEHAVIOR_STATE = new BehaviorState() {
985             @Override
986             RaftActorBehavior getBehavior() {
987                 return null;
988             }
989
990             @Override
991             String getLastValidLeaderId() {
992                 return null;
993             }
994
995             @Override
996             short getLeaderPayloadVersion() {
997                 return -1;
998             }
999
1000             @Override
1001             String getLastLeaderId() {
1002                 return null;
1003             }
1004         };
1005
1006         private String lastValidLeaderId;
1007         private String lastLeaderId;
1008
1009         BehaviorState capture(final RaftActorBehavior behavior) {
1010             if (behavior == null) {
1011                 Verify.verify(lastValidLeaderId == null, "Null behavior with non-null last leader");
1012                 return NULL_BEHAVIOR_STATE;
1013             }
1014
1015             lastLeaderId = behavior.getLeaderId();
1016             if (lastLeaderId != null) {
1017                 lastValidLeaderId = lastLeaderId;
1018             }
1019
1020             return new SimpleBehaviorState(lastValidLeaderId, lastLeaderId, behavior);
1021         }
1022     }
1023
1024 }

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