opendaylight/md-sal/sal-akka-raft/src/main/java/org/opendaylight/controller/cluster/raft/SnapshotManager.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 package org.opendaylight.controller.cluster.raft;
   9
  10 import akka.persistence.SnapshotSelectionCriteria;
  11 import com.google.common.annotations.VisibleForTesting;
  12 import com.google.common.io.ByteSource;
  13 import java.io.IOException;
  14 import java.io.OutputStream;
  15 import java.util.List;
  16 import java.util.Optional;
  17 import java.util.function.Consumer;
  18 import org.eclipse.jdt.annotation.NonNull;
  19 import org.opendaylight.controller.cluster.io.FileBackedOutputStream;
  20 import org.opendaylight.controller.cluster.raft.base.messages.ApplySnapshot;
  21 import org.opendaylight.controller.cluster.raft.base.messages.CaptureSnapshot;
  22 import org.opendaylight.controller.cluster.raft.base.messages.SendInstallSnapshot;
  23 import org.opendaylight.controller.cluster.raft.base.messages.SnapshotComplete;
  24 import org.opendaylight.controller.cluster.raft.behaviors.RaftActorBehavior;
  25 import org.opendaylight.controller.cluster.raft.persisted.EmptyState;
  26 import org.opendaylight.controller.cluster.raft.persisted.Snapshot;
  27 import org.slf4j.Logger;
  28
  29 /**
  30  * Manages the capturing of snapshots for a RaftActor.
  31  *
  32  * @author Moiz Raja
  33  * @author Thomas Pantelis
  34  */
  35 public class SnapshotManager implements SnapshotState {
  36
  37     @SuppressWarnings("checkstyle:MemberName")
  38     private final SnapshotState IDLE = new Idle();
  39
  40     @SuppressWarnings({"checkstyle:MemberName", "checkstyle:AbbreviationAsWordInName"})
  41     private final SnapshotState PERSISTING = new Persisting();
  42
  43     @SuppressWarnings({"checkstyle:MemberName", "checkstyle:AbbreviationAsWordInName"})
  44     private final SnapshotState CREATING = new Creating();
  45
  46     private final Logger log;
  47     private final RaftActorContext context;
  48     private final LastAppliedTermInformationReader lastAppliedTermInformationReader =
  49             new LastAppliedTermInformationReader();
  50     private final ReplicatedToAllTermInformationReader replicatedToAllTermInformationReader =
  51             new ReplicatedToAllTermInformationReader();
  52
  53
  54     private SnapshotState currentState = IDLE;
  55     private CaptureSnapshot captureSnapshot;
  56     private long lastSequenceNumber = -1;
  57
  58     private Consumer<Optional<OutputStream>> createSnapshotProcedure = null;
  59
  60     private ApplySnapshot applySnapshot;
  61     private RaftActorSnapshotCohort snapshotCohort = NoopRaftActorSnapshotCohort.INSTANCE;
  62
  63     /**
  64      * Constructs an instance.
  65      *
  66      * @param context the RaftActorContext
  67      * @param logger the Logger
  68      */
  69     public SnapshotManager(final RaftActorContext context, final Logger logger) {
  70         this.context = context;
  71         this.log = logger;
  72     }
  73
  74     public boolean isApplying() {
  75         return applySnapshot != null;
  76     }
  77
  78     @Override
  79     public boolean isCapturing() {
  80         return currentState.isCapturing();
  81     }
  82
  83     @Override
  84     public boolean captureToInstall(final ReplicatedLogEntry lastLogEntry, final long replicatedToAllIndex,
  85             final String targetFollower) {
  86         return currentState.captureToInstall(lastLogEntry, replicatedToAllIndex, targetFollower);
  87     }
  88
  89     @Override
  90     public boolean capture(final ReplicatedLogEntry lastLogEntry, final long replicatedToAllIndex) {
  91         return currentState.capture(lastLogEntry, replicatedToAllIndex);
  92     }
  93
  94     @Override
  95     public boolean captureWithForcedTrim(final ReplicatedLogEntry lastLogEntry, final long replicatedToAllIndex) {
  96         return currentState.captureWithForcedTrim(lastLogEntry, replicatedToAllIndex);
  97     }
  98
  99     @Override
 100     public void apply(final ApplySnapshot snapshot) {
 101         currentState.apply(snapshot);
 102     }
 103
 104     @Override
 105     public void persist(final Snapshot.State state, final Optional<OutputStream> installSnapshotStream,
 106             final long totalMemory) {
 107         currentState.persist(state, installSnapshotStream, totalMemory);
 108     }
 109
 110     @Override
 111     public void commit(final long sequenceNumber, final long timeStamp) {
 112         currentState.commit(sequenceNumber, timeStamp);
 113     }
 114
 115     @Override
 116     public void rollback() {
 117         currentState.rollback();
 118     }
 119
 120     @Override
 121     public long trimLog(final long desiredTrimIndex) {
 122         return currentState.trimLog(desiredTrimIndex);
 123     }
 124
 125     @SuppressWarnings("checkstyle:hiddenField")
 126     void setCreateSnapshotConsumer(final Consumer<Optional<OutputStream>> createSnapshotProcedure) {
 127         this.createSnapshotProcedure = createSnapshotProcedure;
 128     }
 129
 130     void setSnapshotCohort(final RaftActorSnapshotCohort snapshotCohort) {
 131         this.snapshotCohort = snapshotCohort;
 132     }
 133
 134     public Snapshot.@NonNull State convertSnapshot(final ByteSource snapshotBytes) throws IOException {
 135         return snapshotCohort.deserializeSnapshot(snapshotBytes);
 136     }
 137
 138     public long getLastSequenceNumber() {
 139         return lastSequenceNumber;
 140     }
 141
 142     @VisibleForTesting
 143     public CaptureSnapshot getCaptureSnapshot() {
 144         return captureSnapshot;
 145     }
 146
 147     private boolean hasFollowers() {
 148         return context.hasFollowers();
 149     }
 150
 151     private String persistenceId() {
 152         return context.getId();
 153     }
 154
 155     /**
 156      * Constructs a CaptureSnapshot instance.
 157      *
 158      * @param lastLogEntry the last log entry for the snapshot.
 159      * @param replicatedToAllIndex the index of the last entry replicated to all followers.
 160      * @return a new CaptureSnapshot instance.
 161      */
 162     public CaptureSnapshot newCaptureSnapshot(final ReplicatedLogEntry lastLogEntry, final long replicatedToAllIndex,
 163                                               final boolean mandatoryTrim) {
 164         TermInformationReader lastAppliedTermInfoReader =
 165                 lastAppliedTermInformationReader.init(context.getReplicatedLog(), context.getLastApplied(),
 166                         lastLogEntry, hasFollowers());
 167
 168         long lastAppliedIndex = lastAppliedTermInfoReader.getIndex();
 169         long lastAppliedTerm = lastAppliedTermInfoReader.getTerm();
 170
 171         TermInformationReader replicatedToAllTermInfoReader =
 172                 replicatedToAllTermInformationReader.init(context.getReplicatedLog(), replicatedToAllIndex);
 173
 174         long newReplicatedToAllIndex = replicatedToAllTermInfoReader.getIndex();
 175         long newReplicatedToAllTerm = replicatedToAllTermInfoReader.getTerm();
 176
 177         List<ReplicatedLogEntry> unAppliedEntries = context.getReplicatedLog().getFrom(lastAppliedIndex + 1);
 178
 179         final long lastLogEntryIndex;
 180         final long lastLogEntryTerm;
 181         if (lastLogEntry == null) {
 182             // When we don't have journal present, for example two captureSnapshots executed right after another with no
 183             // new journal we still want to preserve the index and term in the snapshot.
 184             lastAppliedIndex = lastLogEntryIndex = context.getReplicatedLog().getSnapshotIndex();
 185             lastAppliedTerm = lastLogEntryTerm = context.getReplicatedLog().getSnapshotTerm();
 186
 187             log.debug("{}: Capturing Snapshot : lastLogEntry is null. Using snapshot values lastAppliedIndex {} and "
 188                     + "lastAppliedTerm {} instead.", persistenceId(), lastAppliedIndex, lastAppliedTerm);
 189         } else {
 190             lastLogEntryIndex = lastLogEntry.getIndex();
 191             lastLogEntryTerm = lastLogEntry.getTerm();
 192         }
 193
 194         return new CaptureSnapshot(lastLogEntryIndex, lastLogEntryTerm, lastAppliedIndex, lastAppliedTerm,
 195                 newReplicatedToAllIndex, newReplicatedToAllTerm, unAppliedEntries, mandatoryTrim);
 196     }
 197
 198     private class AbstractSnapshotState implements SnapshotState {
 199
 200         @Override
 201         public boolean isCapturing() {
 202             return true;
 203         }
 204
 205         @Override
 206         public boolean capture(final ReplicatedLogEntry lastLogEntry, final long replicatedToAllIndex) {
 207             log.debug("capture should not be called in state {}", this);
 208             return false;
 209         }
 210
 211         @Override
 212         public boolean captureToInstall(final ReplicatedLogEntry lastLogEntry, final long replicatedToAllIndex,
 213                 final String targetFollower) {
 214             log.debug("captureToInstall should not be called in state {}", this);
 215             return false;
 216         }
 217
 218         @Override
 219         public boolean captureWithForcedTrim(final ReplicatedLogEntry lastLogEntry, final long replicatedToAllIndex) {
 220             log.debug("captureWithForcedTrim should not be called in state {}", this);
 221             return false;
 222         }
 223
 224         @Override
 225         public void apply(final ApplySnapshot snapshot) {
 226             log.debug("apply should not be called in state {}", this);
 227         }
 228
 229         @Override
 230         public void persist(final Snapshot.State state, final Optional<OutputStream> installSnapshotStream,
 231                 final long totalMemory) {
 232             log.debug("persist should not be called in state {}", this);
 233         }
 234
 235         @Override
 236         public void commit(final long sequenceNumber, final long timeStamp) {
 237             log.debug("commit should not be called in state {}", this);
 238         }
 239
 240         @Override
 241         public void rollback() {
 242             log.debug("rollback should not be called in state {}", this);
 243         }
 244
 245         @Override
 246         public long trimLog(final long desiredTrimIndex) {
 247             log.debug("trimLog should not be called in state {}", this);
 248             return -1;
 249         }
 250
 251         protected long doTrimLog(final long desiredTrimIndex) {
 252             //  we would want to keep the lastApplied as its used while capturing snapshots
 253             long lastApplied = context.getLastApplied();
 254             long tempMin = Math.min(desiredTrimIndex, lastApplied > -1 ? lastApplied - 1 : -1);
 255
 256             if (log.isTraceEnabled()) {
 257                 log.trace("{}: performSnapshotWithoutCapture: desiredTrimIndex: {}, lastApplied: {}, tempMin: {}",
 258                         persistenceId(), desiredTrimIndex, lastApplied, tempMin);
 259             }
 260
 261             if (tempMin > -1 && context.getReplicatedLog().isPresent(tempMin)) {
 262                 log.debug("{}: fakeSnapshot purging log to {} for term {}", persistenceId(), tempMin,
 263                         context.getTermInformation().getCurrentTerm());
 264
 265                 //use the term of the temp-min, since we check for isPresent, entry will not be null
 266                 ReplicatedLogEntry entry = context.getReplicatedLog().get(tempMin);
 267                 context.getReplicatedLog().snapshotPreCommit(tempMin, entry.getTerm());
 268                 context.getReplicatedLog().snapshotCommit();
 269                 return tempMin;
 270             }
 271
 272             final RaftActorBehavior currentBehavior = context.getCurrentBehavior();
 273             if (tempMin > currentBehavior.getReplicatedToAllIndex()) {
 274                 // It's possible a follower was lagging and an install snapshot advanced its match index past
 275                 // the current replicatedToAllIndex. Since the follower is now caught up we should advance the
 276                 // replicatedToAllIndex (to tempMin). The fact that tempMin wasn't found in the log is likely
 277                 // due to a previous snapshot triggered by the memory threshold exceeded, in that case we
 278                 // trim the log to the last applied index even if previous entries weren't replicated to all followers.
 279                 currentBehavior.setReplicatedToAllIndex(tempMin);
 280             }
 281             return -1;
 282         }
 283     }
 284
 285     private class Idle extends AbstractSnapshotState {
 286
 287         @Override
 288         public boolean isCapturing() {
 289             return false;
 290         }
 291
 292         @SuppressWarnings("checkstyle:IllegalCatch")
 293         private boolean capture(final ReplicatedLogEntry lastLogEntry, final long replicatedToAllIndex,
 294                 final String targetFollower, final boolean mandatoryTrim) {
 295             captureSnapshot = newCaptureSnapshot(lastLogEntry, replicatedToAllIndex, mandatoryTrim);
 296
 297             OutputStream installSnapshotStream = null;
 298             if (targetFollower != null) {
 299                 installSnapshotStream = context.getFileBackedOutputStreamFactory().newInstance();
 300                 log.info("{}: Initiating snapshot capture {} to install on {}",
 301                         persistenceId(), captureSnapshot, targetFollower);
 302             } else {
 303                 log.info("{}: Initiating snapshot capture {}", persistenceId(), captureSnapshot);
 304             }
 305
 306             lastSequenceNumber = context.getPersistenceProvider().getLastSequenceNumber();
 307
 308             log.debug("{}: lastSequenceNumber prior to capture: {}", persistenceId(), lastSequenceNumber);
 309
 310             SnapshotManager.this.currentState = CREATING;
 311
 312             try {
 313                 createSnapshotProcedure.accept(Optional.ofNullable(installSnapshotStream));
 314             } catch (Exception e) {
 315                 SnapshotManager.this.currentState = IDLE;
 316                 log.error("Error creating snapshot", e);
 317                 return false;
 318             }
 319
 320             return true;
 321         }
 322
 323         @Override
 324         public boolean capture(final ReplicatedLogEntry lastLogEntry, final long replicatedToAllIndex) {
 325             return capture(lastLogEntry, replicatedToAllIndex, null, false);
 326         }
 327
 328         @Override
 329         public boolean captureToInstall(final ReplicatedLogEntry lastLogEntry, final long replicatedToAllIndex,
 330                 final String targetFollower) {
 331             return capture(lastLogEntry, replicatedToAllIndex, targetFollower, false);
 332         }
 333
 334         @Override
 335         public boolean captureWithForcedTrim(final ReplicatedLogEntry lastLogEntry, final long replicatedToAllIndex) {
 336             return capture(lastLogEntry, replicatedToAllIndex, null, true);
 337         }
 338
 339         @Override
 340         public void apply(final ApplySnapshot toApply) {
 341             SnapshotManager.this.applySnapshot = toApply;
 342
 343             lastSequenceNumber = context.getPersistenceProvider().getLastSequenceNumber();
 344
 345             log.debug("lastSequenceNumber prior to persisting applied snapshot: {}", lastSequenceNumber);
 346
 347             context.getPersistenceProvider().saveSnapshot(toApply.getSnapshot());
 348
 349             SnapshotManager.this.currentState = PERSISTING;
 350         }
 351
 352         @Override
 353         public String toString() {
 354             return "Idle";
 355         }
 356
 357         @Override
 358         public long trimLog(final long desiredTrimIndex) {
 359             return doTrimLog(desiredTrimIndex);
 360         }
 361     }
 362
 363     private class Creating extends AbstractSnapshotState {
 364
 365         @Override
 366         public void persist(final Snapshot.State snapshotState, final Optional<OutputStream> installSnapshotStream,
 367                 final long totalMemory) {
 368             // create a snapshot object from the state provided and save it
 369             // when snapshot is saved async, SaveSnapshotSuccess is raised.
 370
 371             Snapshot snapshot = Snapshot.create(snapshotState,
 372                     captureSnapshot.getUnAppliedEntries(),
 373                     captureSnapshot.getLastIndex(), captureSnapshot.getLastTerm(),
 374                     captureSnapshot.getLastAppliedIndex(), captureSnapshot.getLastAppliedTerm(),
 375                     context.getTermInformation().getCurrentTerm(),
 376                     context.getTermInformation().getVotedFor(), context.getPeerServerInfo(true));
 377
 378             context.getPersistenceProvider().saveSnapshot(snapshot);
 379
 380             log.info("{}: Persisting of snapshot done: {}", persistenceId(), snapshot);
 381
 382             final ConfigParams config = context.getConfigParams();
 383             final long absoluteThreshold = config.getSnapshotDataThreshold();
 384             final long dataThreshold = absoluteThreshold != 0 ? absoluteThreshold * ConfigParams.MEGABYTE
 385                     : totalMemory * config.getSnapshotDataThresholdPercentage() / 100;
 386
 387             final boolean dataSizeThresholdExceeded = context.getReplicatedLog().dataSize() > dataThreshold;
 388             final boolean logSizeExceededSnapshotBatchCount =
 389                     context.getReplicatedLog().size() >= config.getSnapshotBatchCount();
 390
 391             final RaftActorBehavior currentBehavior = context.getCurrentBehavior();
 392             if (dataSizeThresholdExceeded || logSizeExceededSnapshotBatchCount || captureSnapshot.isMandatoryTrim()) {
 393                 if (log.isDebugEnabled()) {
 394                     if (dataSizeThresholdExceeded) {
 395                         log.debug("{}: log data size {} exceeds the memory threshold {} - doing snapshotPreCommit "
 396                                 + "with index {}", context.getId(), context.getReplicatedLog().dataSize(),
 397                                 dataThreshold, captureSnapshot.getLastAppliedIndex());
 398                     } else if (logSizeExceededSnapshotBatchCount) {
 399                         log.debug("{}: log size {} exceeds the snapshot batch count {} - doing snapshotPreCommit with "
 400                                 + "index {}", context.getId(), context.getReplicatedLog().size(),
 401                                 config.getSnapshotBatchCount(), captureSnapshot.getLastAppliedIndex());
 402                     } else {
 403                         log.debug("{}: user triggered or root overwrite snapshot encountered, trimming log up to "
 404                                 + "last applied index {}", context.getId(), captureSnapshot.getLastAppliedIndex());
 405                     }
 406                 }
 407
 408                 // We either exceeded the memory threshold or the log size exceeded the snapshot batch
 409                 // count so, to keep the log memory footprint in check, clear the log based on lastApplied.
 410                 // This could/should only happen if one of the followers is down as normally we keep
 411                 // removing from the log as entries are replicated to all.
 412                 context.getReplicatedLog().snapshotPreCommit(captureSnapshot.getLastAppliedIndex(),
 413                         captureSnapshot.getLastAppliedTerm());
 414
 415                 // Don't reset replicatedToAllIndex to -1 as this may prevent us from trimming the log after an
 416                 // install snapshot to a follower.
 417                 if (captureSnapshot.getReplicatedToAllIndex() >= 0) {
 418                     currentBehavior.setReplicatedToAllIndex(captureSnapshot.getReplicatedToAllIndex());
 419                 }
 420
 421             } else if (captureSnapshot.getReplicatedToAllIndex() != -1) {
 422                 // clear the log based on replicatedToAllIndex
 423                 context.getReplicatedLog().snapshotPreCommit(captureSnapshot.getReplicatedToAllIndex(),
 424                         captureSnapshot.getReplicatedToAllTerm());
 425
 426                 currentBehavior.setReplicatedToAllIndex(captureSnapshot.getReplicatedToAllIndex());
 427             } else {
 428                 // The replicatedToAllIndex was not found in the log
 429                 // This means that replicatedToAllIndex never moved beyond -1 or that it is already in the snapshot.
 430                 // In this scenario we may need to save the snapshot to the akka persistence
 431                 // snapshot for recovery but we do not need to do the replicated log trimming.
 432                 context.getReplicatedLog().snapshotPreCommit(context.getReplicatedLog().getSnapshotIndex(),
 433                         context.getReplicatedLog().getSnapshotTerm());
 434             }
 435
 436             log.info("{}: Removed in-memory snapshotted entries, adjusted snaphsotIndex: {} and term: {}",
 437                     context.getId(), context.getReplicatedLog().getSnapshotIndex(),
 438                     context.getReplicatedLog().getSnapshotTerm());
 439
 440             if (installSnapshotStream.isPresent()) {
 441                 if (context.getId().equals(currentBehavior.getLeaderId())) {
 442                     try {
 443                         ByteSource snapshotBytes = ((FileBackedOutputStream)installSnapshotStream.get()).asByteSource();
 444                         currentBehavior.handleMessage(context.getActor(),
 445                                 new SendInstallSnapshot(snapshot, snapshotBytes));
 446                     } catch (IOException e) {
 447                         log.error("{}: Snapshot install failed due to an unrecoverable streaming error",
 448                                 context.getId(), e);
 449                     }
 450                 } else {
 451                     ((FileBackedOutputStream)installSnapshotStream.get()).cleanup();
 452                 }
 453             }
 454
 455             captureSnapshot = null;
 456             SnapshotManager.this.currentState = PERSISTING;
 457         }
 458
 459         @Override
 460         public String toString() {
 461             return "Creating";
 462         }
 463
 464     }
 465
 466     private class Persisting extends AbstractSnapshotState {
 467
 468         @Override
 469         @SuppressWarnings("checkstyle:IllegalCatch")
 470         public void commit(final long sequenceNumber, final long timeStamp) {
 471             log.debug("{}: Snapshot success -  sequence number: {}", persistenceId(), sequenceNumber);
 472
 473             if (applySnapshot != null) {
 474                 try {
 475                     Snapshot snapshot = applySnapshot.getSnapshot();
 476
 477                     //clears the followers log, sets the snapshot index to ensure adjusted-index works
 478                     context.setReplicatedLog(ReplicatedLogImpl.newInstance(snapshot, context));
 479                     context.setLastApplied(snapshot.getLastAppliedIndex());
 480                     context.setCommitIndex(snapshot.getLastAppliedIndex());
 481                     context.getTermInformation().update(snapshot.getElectionTerm(), snapshot.getElectionVotedFor());
 482
 483                     if (snapshot.getServerConfiguration() != null) {
 484                         context.updatePeerIds(snapshot.getServerConfiguration());
 485                     }
 486
 487                     if (!(snapshot.getState() instanceof EmptyState)) {
 488                         snapshotCohort.applySnapshot(snapshot.getState());
 489                     }
 490
 491                     applySnapshot.getCallback().onSuccess();
 492                 } catch (Exception e) {
 493                     log.error("{}: Error applying snapshot", context.getId(), e);
 494                 }
 495             } else {
 496                 context.getReplicatedLog().snapshotCommit();
 497             }
 498
 499             context.getPersistenceProvider().deleteSnapshots(new SnapshotSelectionCriteria(scala.Long.MaxValue(),
 500                     timeStamp - 1, 0L, 0L));
 501
 502             context.getPersistenceProvider().deleteMessages(lastSequenceNumber);
 503
 504             snapshotComplete();
 505         }
 506
 507         @Override
 508         public void rollback() {
 509             // Nothing to rollback if we're applying a snapshot from the leader.
 510             if (applySnapshot == null) {
 511                 context.getReplicatedLog().snapshotRollback();
 512
 513                 log.info("{}: Replicated Log rolled back. Snapshot will be attempted in the next cycle."
 514                         + "snapshotIndex:{}, snapshotTerm:{}, log-size:{}", persistenceId(),
 515                         context.getReplicatedLog().getSnapshotIndex(),
 516                         context.getReplicatedLog().getSnapshotTerm(),
 517                         context.getReplicatedLog().size());
 518             } else {
 519                 applySnapshot.getCallback().onFailure();
 520             }
 521
 522             snapshotComplete();
 523         }
 524
 525         private void snapshotComplete() {
 526             lastSequenceNumber = -1;
 527             applySnapshot = null;
 528             SnapshotManager.this.currentState = IDLE;
 529
 530             context.getActor().tell(SnapshotComplete.INSTANCE, context.getActor());
 531         }
 532
 533         @Override
 534         public String toString() {
 535             return "Persisting";
 536         }
 537
 538     }
 539
 540     private interface TermInformationReader {
 541         long getIndex();
 542
 543         long getTerm();
 544     }
 545
 546     static class LastAppliedTermInformationReader implements TermInformationReader {
 547         private long index;
 548         private long term;
 549
 550         LastAppliedTermInformationReader init(final ReplicatedLog log, final long originalIndex,
 551                 final ReplicatedLogEntry lastLogEntry, final boolean hasFollowers) {
 552             ReplicatedLogEntry entry = log.get(originalIndex);
 553             this.index = -1L;
 554             this.term = -1L;
 555             if (!hasFollowers) {
 556                 if (lastLogEntry != null) {
 557                     // since we have persisted the last-log-entry to persistent journal before the capture,
 558                     // we would want to snapshot from this entry.
 559                     index = lastLogEntry.getIndex();
 560                     term = lastLogEntry.getTerm();
 561                 }
 562             } else if (entry != null) {
 563                 index = entry.getIndex();
 564                 term = entry.getTerm();
 565             } else if (log.getSnapshotIndex() > -1) {
 566                 index = log.getSnapshotIndex();
 567                 term = log.getSnapshotTerm();
 568             }
 569             return this;
 570         }
 571
 572         @Override
 573         public long getIndex() {
 574             return this.index;
 575         }
 576
 577         @Override
 578         public long getTerm() {
 579             return this.term;
 580         }
 581     }
 582
 583     private static class ReplicatedToAllTermInformationReader implements TermInformationReader {
 584         private long index;
 585         private long term;
 586
 587         ReplicatedToAllTermInformationReader init(final ReplicatedLog log, final long originalIndex) {
 588             ReplicatedLogEntry entry = log.get(originalIndex);
 589             this.index = -1L;
 590             this.term = -1L;
 591
 592             if (entry != null) {
 593                 index = entry.getIndex();
 594                 term = entry.getTerm();
 595             }
 596
 597             return this;
 598         }
 599
 600         @Override
 601         public long getIndex() {
 602             return this.index;
 603         }
 604
 605         @Override
 606         public long getTerm() {
 607             return this.term;
 608         }
 609     }
 610 }