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 com.google.common.annotations.VisibleForTesting;
  13 import java.util.ArrayList;
  14 import org.opendaylight.controller.cluster.raft.RaftActorContext;
  15 import org.opendaylight.controller.cluster.raft.RaftState;
  16 import org.opendaylight.controller.cluster.raft.ReplicatedLogEntry;
  17 import org.opendaylight.controller.cluster.raft.Snapshot;
  18 import org.opendaylight.controller.cluster.raft.base.messages.ApplySnapshot;
  19 import org.opendaylight.controller.cluster.raft.base.messages.ElectionTimeout;
  20 import org.opendaylight.controller.cluster.raft.base.messages.FollowerInitialSyncUpStatus;
  21 import org.opendaylight.controller.cluster.raft.messages.AppendEntries;
  22 import org.opendaylight.controller.cluster.raft.messages.AppendEntriesReply;
  23 import org.opendaylight.controller.cluster.raft.messages.InstallSnapshot;
  24 import org.opendaylight.controller.cluster.raft.messages.InstallSnapshotReply;
  25 import org.opendaylight.controller.cluster.raft.messages.RaftRPC;
  26 import org.opendaylight.controller.cluster.raft.messages.RequestVoteReply;
  27
  28 /**
  29  * The behavior of a RaftActor in the Follower state
  30  * <p/>
  31  * <ul>
  32  * <li> Respond to RPCs from candidates and leaders
  33  * <li> If election timeout elapses without receiving AppendEntries
  34  * RPC from current leader or granting vote to candidate:
  35  * convert to candidate
  36  * </ul>
  37  */
  38 public class Follower extends AbstractRaftActorBehavior {
  39
  40
  41
  42     private SnapshotTracker snapshotTracker = null;
  43
  44     private final InitialSyncStatusTracker initialSyncStatusTracker;
  45
  46     public Follower(RaftActorContext context) {
  47         super(context, RaftState.Follower);
  48
  49         initialSyncStatusTracker = new InitialSyncStatusTracker(context.getActor());
  50
  51         if(context.getPeerAddresses().isEmpty()){
  52             actor().tell(ELECTION_TIMEOUT, actor());
  53         } else {
  54             scheduleElection(electionDuration());
  55         }
  56
  57     }
  58
  59     private boolean isLogEntryPresent(long index){
  60         if(index == context.getReplicatedLog().getSnapshotIndex()){
  61             return true;
  62         }
  63
  64         ReplicatedLogEntry previousEntry = context.getReplicatedLog()
  65                 .get(index);
  66
  67         return previousEntry != null;
  68
  69     }
  70
  71     private long getLogEntryTerm(long index){
  72         if(index == context.getReplicatedLog().getSnapshotIndex()){
  73             return context.getReplicatedLog().getSnapshotTerm();
  74         }
  75
  76         ReplicatedLogEntry previousEntry = context.getReplicatedLog()
  77                 .get(index);
  78
  79         if(previousEntry != null){
  80             return previousEntry.getTerm();
  81         }
  82
  83         return -1;
  84     }
  85
  86     private void updateInitialSyncStatus(long currentLeaderCommit, String leaderId){
  87         initialSyncStatusTracker.update(leaderId, currentLeaderCommit, context.getCommitIndex());
  88     }
  89
  90     @Override protected RaftActorBehavior handleAppendEntries(ActorRef sender,
  91                                                               AppendEntries appendEntries) {
  92
  93         int numLogEntries = appendEntries.getEntries() != null ? appendEntries.getEntries().size() : 0;
  94         if(LOG.isTraceEnabled()) {
  95             LOG.trace("{}: handleAppendEntries: {}", logName(), appendEntries);
  96         } else if(LOG.isDebugEnabled() && numLogEntries > 0) {
  97             LOG.debug("{}: handleAppendEntries: {}", logName(), appendEntries);
  98         }
  99
 100         // TODO : Refactor this method into a bunch of smaller methods
 101         // to make it easier to read. Before refactoring ensure tests
 102         // cover the code properly
 103
 104         if (snapshotTracker != null) {
 105             // if snapshot install is in progress, follower should just acknowledge append entries with a reply.
 106             AppendEntriesReply reply = new AppendEntriesReply(context.getId(), currentTerm(), true,
 107                     lastIndex(), lastTerm());
 108
 109             if(LOG.isDebugEnabled()) {
 110                 LOG.debug("{}: snapshot install is in progress, replying immediately with {}", logName(), reply);
 111             }
 112             sender.tell(reply, actor());
 113
 114             return this;
 115         }
 116
 117         // 1. Reply false if term < currentTerm (§5.1)
 118         // This is handled in the appendEntries method of the base class
 119
 120         // If we got here then we do appear to be talking to the leader
 121         leaderId = appendEntries.getLeaderId();
 122
 123         // 2. Reply false if log doesn’t contain an entry at prevLogIndex
 124         // whose term matches prevLogTerm (§5.3)
 125
 126         long prevLogTerm = getLogEntryTerm(appendEntries.getPrevLogIndex());
 127         boolean prevEntryPresent = isLogEntryPresent(appendEntries.getPrevLogIndex());
 128
 129         updateInitialSyncStatus(appendEntries.getLeaderCommit(), appendEntries.getLeaderId());
 130
 131         boolean outOfSync = true;
 132
 133         // First check if the logs are in sync or not
 134         long lastIndex = lastIndex();
 135         if (lastIndex == -1 && appendEntries.getPrevLogIndex() != -1) {
 136
 137             // The follower's log is out of sync because the leader does have
 138             // an entry at prevLogIndex and this follower has no entries in
 139             // it's log.
 140
 141             LOG.debug("{}: The followers log is empty and the senders prevLogIndex is {}",
 142                         logName(), appendEntries.getPrevLogIndex());
 143         } else if (lastIndex > -1 && appendEntries.getPrevLogIndex() != -1 && !prevEntryPresent) {
 144
 145             // The follower's log is out of sync because the Leader's
 146             // prevLogIndex entry was not found in it's log
 147
 148             LOG.debug("{}: The log is not empty but the prevLogIndex {} was not found in it",
 149                         logName(), appendEntries.getPrevLogIndex());
 150         } else if (lastIndex > -1 && prevEntryPresent && prevLogTerm != appendEntries.getPrevLogTerm()) {
 151
 152             // The follower's log is out of sync because the Leader's
 153             // prevLogIndex entry does exist in the follower's log but it has
 154             // a different term in it
 155
 156             LOG.debug(
 157                 "{}: Cannot append entries because previous entry term {}  is not equal to append entries prevLogTerm {}",
 158                  logName(), prevLogTerm, appendEntries.getPrevLogTerm());
 159         } else {
 160             outOfSync = false;
 161         }
 162
 163         if (outOfSync) {
 164             // We found that the log was out of sync so just send a negative
 165             // reply and return
 166
 167             LOG.debug("{}: Follower is out-of-sync, so sending negative reply, lastIndex: {}, lastTerm: {}",
 168                         logName(), lastIndex, lastTerm());
 169
 170             sender.tell(new AppendEntriesReply(context.getId(), currentTerm(), false, lastIndex,
 171                     lastTerm()), actor());
 172             return this;
 173         }
 174
 175         if (appendEntries.getEntries() != null && appendEntries.getEntries().size() > 0) {
 176
 177             LOG.debug("{}: Number of entries to be appended = {}", logName(),
 178                         appendEntries.getEntries().size());
 179
 180             // 3. If an existing entry conflicts with a new one (same index
 181             // but different terms), delete the existing entry and all that
 182             // follow it (§5.3)
 183             int addEntriesFrom = 0;
 184             if (context.getReplicatedLog().size() > 0) {
 185
 186                 // Find the entry up until which the one that is not in the follower's log
 187                 for (int i = 0;i < appendEntries.getEntries().size(); i++, addEntriesFrom++) {
 188                     ReplicatedLogEntry matchEntry = appendEntries.getEntries().get(i);
 189                     ReplicatedLogEntry newEntry = context.getReplicatedLog().get(matchEntry.getIndex());
 190
 191                     if (newEntry == null) {
 192                         //newEntry not found in the log
 193                         break;
 194                     }
 195
 196                     if (newEntry.getTerm() == matchEntry.getTerm()) {
 197                         continue;
 198                     }
 199
 200                     LOG.debug("{}: Removing entries from log starting at {}", logName(),
 201                                 matchEntry.getIndex());
 202
 203                     // Entries do not match so remove all subsequent entries
 204                     context.getReplicatedLog().removeFromAndPersist(matchEntry.getIndex());
 205                     break;
 206                 }
 207             }
 208
 209             lastIndex = lastIndex();
 210             LOG.debug("{}: After cleanup entries to be added from = {}", logName(),
 211                         (addEntriesFrom + lastIndex));
 212
 213             // 4. Append any new entries not already in the log
 214             for (int i = addEntriesFrom; i < appendEntries.getEntries().size(); i++) {
 215                 ReplicatedLogEntry entry = appendEntries.getEntries().get(i);
 216
 217                 LOG.debug("{}: Append entry to log {}", logName(), entry.getData());
 218
 219                 context.getReplicatedLog().appendAndPersist(entry);
 220             }
 221
 222             LOG.debug("{}: Log size is now {}", logName(), context.getReplicatedLog().size());
 223         }
 224
 225         // 5. If leaderCommit > commitIndex, set commitIndex =
 226         // min(leaderCommit, index of last new entry)
 227
 228         lastIndex = lastIndex();
 229         long prevCommitIndex = context.getCommitIndex();
 230
 231         context.setCommitIndex(Math.min(appendEntries.getLeaderCommit(), lastIndex));
 232
 233         if (prevCommitIndex != context.getCommitIndex()) {
 234             LOG.debug("{}: Commit index set to {}", logName(), context.getCommitIndex());
 235         }
 236
 237         // If commitIndex > lastApplied: increment lastApplied, apply
 238         // log[lastApplied] to state machine (§5.3)
 239         // check if there are any entries to be applied. last-applied can be equal to last-index
 240         if (appendEntries.getLeaderCommit() > context.getLastApplied() &&
 241             context.getLastApplied() < lastIndex) {
 242             if(LOG.isDebugEnabled()) {
 243                 LOG.debug("{}: applyLogToStateMachine, " +
 244                         "appendEntries.getLeaderCommit(): {}," +
 245                         "context.getLastApplied(): {}, lastIndex(): {}", logName(),
 246                     appendEntries.getLeaderCommit(), context.getLastApplied(), lastIndex);
 247             }
 248
 249             applyLogToStateMachine(appendEntries.getLeaderCommit());
 250         }
 251
 252         AppendEntriesReply reply = new AppendEntriesReply(context.getId(), currentTerm(), true,
 253             lastIndex, lastTerm());
 254
 255         if(LOG.isTraceEnabled()) {
 256             LOG.trace("{}: handleAppendEntries returning : {}", logName(), reply);
 257         } else if(LOG.isDebugEnabled() && numLogEntries > 0) {
 258             LOG.debug("{}: handleAppendEntries returning : {}", logName(), reply);
 259         }
 260
 261         sender.tell(reply, actor());
 262
 263         if (!context.getSnapshotManager().isCapturing()) {
 264             super.performSnapshotWithoutCapture(appendEntries.getReplicatedToAllIndex());
 265         }
 266
 267         return this;
 268     }
 269
 270     @Override protected RaftActorBehavior handleAppendEntriesReply(ActorRef sender,
 271         AppendEntriesReply appendEntriesReply) {
 272         return this;
 273     }
 274
 275     @Override protected RaftActorBehavior handleRequestVoteReply(ActorRef sender,
 276         RequestVoteReply requestVoteReply) {
 277         return this;
 278     }
 279
 280     @Override public RaftActorBehavior handleMessage(ActorRef sender, Object originalMessage) {
 281
 282         Object message = fromSerializableMessage(originalMessage);
 283
 284         if (message instanceof RaftRPC) {
 285             RaftRPC rpc = (RaftRPC) message;
 286             // If RPC request or response contains term T > currentTerm:
 287             // set currentTerm = T, convert to follower (§5.1)
 288             // This applies to all RPC messages and responses
 289             if (rpc.getTerm() > context.getTermInformation().getCurrentTerm()) {
 290                 LOG.debug("{}: Term {} in \"{}\" message is greater than follower's term {} - updating term",
 291                         logName(), rpc.getTerm(), rpc, context.getTermInformation().getCurrentTerm());
 292
 293                 context.getTermInformation().updateAndPersist(rpc.getTerm(), null);
 294             }
 295         }
 296
 297         if (message instanceof ElectionTimeout) {
 298             LOG.debug("{}: Received ElectionTimeout - switching to Candidate", logName());
 299             return switchBehavior(new Candidate(context));
 300
 301         } else if (message instanceof InstallSnapshot) {
 302             InstallSnapshot installSnapshot = (InstallSnapshot) message;
 303             handleInstallSnapshot(sender, installSnapshot);
 304         }
 305
 306         scheduleElection(electionDuration());
 307
 308         return super.handleMessage(sender, message);
 309     }
 310
 311     private void handleInstallSnapshot(ActorRef sender, InstallSnapshot installSnapshot) {
 312
 313         LOG.debug("{}: InstallSnapshot received from leader {}, datasize: {} , Chunk: {}/{}",
 314                     logName(), installSnapshot.getLeaderId(), installSnapshot.getData().size(),
 315                     installSnapshot.getChunkIndex(), installSnapshot.getTotalChunks());
 316
 317         if(snapshotTracker == null){
 318             snapshotTracker = new SnapshotTracker(LOG, installSnapshot.getTotalChunks());
 319         }
 320
 321         updateInitialSyncStatus(installSnapshot.getLastIncludedIndex(), installSnapshot.getLeaderId());
 322
 323         try {
 324             if(snapshotTracker.addChunk(installSnapshot.getChunkIndex(), installSnapshot.getData(),
 325                     installSnapshot.getLastChunkHashCode())){
 326                 Snapshot snapshot = Snapshot.create(snapshotTracker.getSnapshot(),
 327                         new ArrayList<ReplicatedLogEntry>(),
 328                         installSnapshot.getLastIncludedIndex(),
 329                         installSnapshot.getLastIncludedTerm(),
 330                         installSnapshot.getLastIncludedIndex(),
 331                         installSnapshot.getLastIncludedTerm());
 332
 333                 actor().tell(new ApplySnapshot(snapshot), actor());
 334
 335                 snapshotTracker = null;
 336
 337             }
 338
 339             InstallSnapshotReply reply = new InstallSnapshotReply(
 340                     currentTerm(), context.getId(), installSnapshot.getChunkIndex(), true);
 341
 342             LOG.debug("{}: handleInstallSnapshot returning: {}", logName(), reply);
 343
 344             sender.tell(reply, actor());
 345
 346         } catch (SnapshotTracker.InvalidChunkException e) {
 347             LOG.debug("{}: Exception in InstallSnapshot of follower", logName(), e);
 348
 349             sender.tell(new InstallSnapshotReply(currentTerm(), context.getId(),
 350                     -1, false), actor());
 351             snapshotTracker = null;
 352
 353         } catch (Exception e){
 354             LOG.error("{}: Exception in InstallSnapshot of follower", logName(), e);
 355
 356             //send reply with success as false. The chunk will be sent again on failure
 357             sender.tell(new InstallSnapshotReply(currentTerm(), context.getId(),
 358                     installSnapshot.getChunkIndex(), false), actor());
 359
 360         }
 361     }
 362
 363     @Override
 364     public void close() throws Exception {
 365         stopElection();
 366     }
 367
 368     @VisibleForTesting
 369     SnapshotTracker getSnapshotTracker(){
 370         return snapshotTracker;
 371     }
 372
 373     private class InitialSyncStatusTracker {
 374
 375         private static final long INVALID_LOG_INDEX = -2L;
 376         private long initialLeaderCommit = INVALID_LOG_INDEX;
 377         private boolean initialSyncUpDone = false;
 378         private String syncedLeaderId = null;
 379         private final ActorRef actor;
 380
 381         public InitialSyncStatusTracker(ActorRef actor) {
 382             this.actor = actor;
 383         }
 384
 385         public void update(String leaderId, long leaderCommit, long commitIndex){
 386
 387             if(!leaderId.equals(syncedLeaderId)){
 388                 initialSyncUpDone = false;
 389                 initialLeaderCommit = INVALID_LOG_INDEX;
 390                 syncedLeaderId = leaderId;
 391             }
 392
 393             if(!initialSyncUpDone){
 394                 if(initialLeaderCommit == INVALID_LOG_INDEX){
 395                     actor.tell(new FollowerInitialSyncUpStatus(false, getId()), ActorRef.noSender());
 396                     initialLeaderCommit = leaderCommit;
 397                 } else if(commitIndex >= initialLeaderCommit){
 398                     actor.tell(new FollowerInitialSyncUpStatus(true, getId()), ActorRef.noSender());
 399                     initialSyncUpDone = true;
 400                 }
 401             }
 402         }
 403     }
 404 }