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(), context.getPayloadVersion());
 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         setLeaderPayloadVersion(appendEntries.getPayloadVersion());
 124
 125         // 2. Reply false if log doesn’t contain an entry at prevLogIndex
 126         // whose term matches prevLogTerm (§5.3)
 127
 128         long prevLogTerm = getLogEntryTerm(appendEntries.getPrevLogIndex());
 129         boolean prevEntryPresent = isLogEntryPresent(appendEntries.getPrevLogIndex());
 130
 131         updateInitialSyncStatus(appendEntries.getLeaderCommit(), appendEntries.getLeaderId());
 132
 133         boolean outOfSync = true;
 134
 135         // First check if the logs are in sync or not
 136         long lastIndex = lastIndex();
 137         if (lastIndex == -1 && appendEntries.getPrevLogIndex() != -1) {
 138
 139             // The follower's log is out of sync because the leader does have
 140             // an entry at prevLogIndex and this follower has no entries in
 141             // it's log.
 142
 143             LOG.debug("{}: The followers log is empty and the senders prevLogIndex is {}",
 144                         logName(), appendEntries.getPrevLogIndex());
 145         } else if (lastIndex > -1 && appendEntries.getPrevLogIndex() != -1 && !prevEntryPresent) {
 146
 147             // The follower's log is out of sync because the Leader's
 148             // prevLogIndex entry was not found in it's log
 149
 150             LOG.debug("{}: The log is not empty but the prevLogIndex {} was not found in it",
 151                         logName(), appendEntries.getPrevLogIndex());
 152         } else if (lastIndex > -1 && prevEntryPresent && prevLogTerm != appendEntries.getPrevLogTerm()) {
 153
 154             // The follower's log is out of sync because the Leader's
 155             // prevLogIndex entry does exist in the follower's log but it has
 156             // a different term in it
 157
 158             LOG.debug(
 159                 "{}: Cannot append entries because previous entry term {}  is not equal to append entries prevLogTerm {}",
 160                  logName(), prevLogTerm, appendEntries.getPrevLogTerm());
 161         } else {
 162             outOfSync = false;
 163         }
 164
 165         if (outOfSync) {
 166             // We found that the log was out of sync so just send a negative
 167             // reply and return
 168
 169             LOG.debug("{}: Follower is out-of-sync, so sending negative reply, lastIndex: {}, lastTerm: {}",
 170                         logName(), lastIndex, lastTerm());
 171
 172             sender.tell(new AppendEntriesReply(context.getId(), currentTerm(), false, lastIndex,
 173                     lastTerm(), context.getPayloadVersion()), actor());
 174             return this;
 175         }
 176
 177         if (appendEntries.getEntries() != null && appendEntries.getEntries().size() > 0) {
 178
 179             LOG.debug("{}: Number of entries to be appended = {}", logName(),
 180                         appendEntries.getEntries().size());
 181
 182             // 3. If an existing entry conflicts with a new one (same index
 183             // but different terms), delete the existing entry and all that
 184             // follow it (§5.3)
 185             int addEntriesFrom = 0;
 186             if (context.getReplicatedLog().size() > 0) {
 187
 188                 // Find the entry up until which the one that is not in the follower's log
 189                 for (int i = 0;i < appendEntries.getEntries().size(); i++, addEntriesFrom++) {
 190                     ReplicatedLogEntry matchEntry = appendEntries.getEntries().get(i);
 191                     ReplicatedLogEntry newEntry = context.getReplicatedLog().get(matchEntry.getIndex());
 192
 193                     if (newEntry == null) {
 194                         //newEntry not found in the log
 195                         break;
 196                     }
 197
 198                     if (newEntry.getTerm() == matchEntry.getTerm()) {
 199                         continue;
 200                     }
 201
 202                     LOG.debug("{}: Removing entries from log starting at {}", logName(),
 203                                 matchEntry.getIndex());
 204
 205                     // Entries do not match so remove all subsequent entries
 206                     context.getReplicatedLog().removeFromAndPersist(matchEntry.getIndex());
 207                     break;
 208                 }
 209             }
 210
 211             lastIndex = lastIndex();
 212             LOG.debug("{}: After cleanup entries to be added from = {}", logName(),
 213                         (addEntriesFrom + lastIndex));
 214
 215             // 4. Append any new entries not already in the log
 216             for (int i = addEntriesFrom; i < appendEntries.getEntries().size(); i++) {
 217                 ReplicatedLogEntry entry = appendEntries.getEntries().get(i);
 218
 219                 LOG.debug("{}: Append entry to log {}", logName(), entry.getData());
 220
 221                 context.getReplicatedLog().appendAndPersist(entry);
 222             }
 223
 224             LOG.debug("{}: Log size is now {}", logName(), context.getReplicatedLog().size());
 225         }
 226
 227         // 5. If leaderCommit > commitIndex, set commitIndex =
 228         // min(leaderCommit, index of last new entry)
 229
 230         lastIndex = lastIndex();
 231         long prevCommitIndex = context.getCommitIndex();
 232
 233         context.setCommitIndex(Math.min(appendEntries.getLeaderCommit(), lastIndex));
 234
 235         if (prevCommitIndex != context.getCommitIndex()) {
 236             LOG.debug("{}: Commit index set to {}", logName(), context.getCommitIndex());
 237         }
 238
 239         // If commitIndex > lastApplied: increment lastApplied, apply
 240         // log[lastApplied] to state machine (§5.3)
 241         // check if there are any entries to be applied. last-applied can be equal to last-index
 242         if (appendEntries.getLeaderCommit() > context.getLastApplied() &&
 243             context.getLastApplied() < lastIndex) {
 244             if(LOG.isDebugEnabled()) {
 245                 LOG.debug("{}: applyLogToStateMachine, " +
 246                         "appendEntries.getLeaderCommit(): {}," +
 247                         "context.getLastApplied(): {}, lastIndex(): {}", logName(),
 248                     appendEntries.getLeaderCommit(), context.getLastApplied(), lastIndex);
 249             }
 250
 251             applyLogToStateMachine(appendEntries.getLeaderCommit());
 252         }
 253
 254         AppendEntriesReply reply = new AppendEntriesReply(context.getId(), currentTerm(), true,
 255             lastIndex, lastTerm(), context.getPayloadVersion());
 256
 257         if(LOG.isTraceEnabled()) {
 258             LOG.trace("{}: handleAppendEntries returning : {}", logName(), reply);
 259         } else if(LOG.isDebugEnabled() && numLogEntries > 0) {
 260             LOG.debug("{}: handleAppendEntries returning : {}", logName(), reply);
 261         }
 262
 263         sender.tell(reply, actor());
 264
 265         if (!context.getSnapshotManager().isCapturing()) {
 266             super.performSnapshotWithoutCapture(appendEntries.getReplicatedToAllIndex());
 267         }
 268
 269         return this;
 270     }
 271
 272     @Override protected RaftActorBehavior handleAppendEntriesReply(ActorRef sender,
 273         AppendEntriesReply appendEntriesReply) {
 274         return this;
 275     }
 276
 277     @Override protected RaftActorBehavior handleRequestVoteReply(ActorRef sender,
 278         RequestVoteReply requestVoteReply) {
 279         return this;
 280     }
 281
 282     @Override public RaftActorBehavior handleMessage(ActorRef sender, Object originalMessage) {
 283
 284         Object message = fromSerializableMessage(originalMessage);
 285
 286         if (message instanceof RaftRPC) {
 287             RaftRPC rpc = (RaftRPC) message;
 288             // If RPC request or response contains term T > currentTerm:
 289             // set currentTerm = T, convert to follower (§5.1)
 290             // This applies to all RPC messages and responses
 291             if (rpc.getTerm() > context.getTermInformation().getCurrentTerm()) {
 292                 LOG.debug("{}: Term {} in \"{}\" message is greater than follower's term {} - updating term",
 293                         logName(), rpc.getTerm(), rpc, context.getTermInformation().getCurrentTerm());
 294
 295                 context.getTermInformation().updateAndPersist(rpc.getTerm(), null);
 296             }
 297         }
 298
 299         if (message instanceof ElectionTimeout) {
 300             LOG.debug("{}: Received ElectionTimeout - switching to Candidate", logName());
 301             return switchBehavior(new Candidate(context));
 302
 303         } else if (message instanceof InstallSnapshot) {
 304             InstallSnapshot installSnapshot = (InstallSnapshot) message;
 305             handleInstallSnapshot(sender, installSnapshot);
 306         }
 307
 308         scheduleElection(electionDuration());
 309
 310         return super.handleMessage(sender, message);
 311     }
 312
 313     private void handleInstallSnapshot(ActorRef sender, InstallSnapshot installSnapshot) {
 314
 315         LOG.debug("{}: InstallSnapshot received from leader {}, datasize: {} , Chunk: {}/{}",
 316                     logName(), installSnapshot.getLeaderId(), installSnapshot.getData().size(),
 317                     installSnapshot.getChunkIndex(), installSnapshot.getTotalChunks());
 318
 319         if(snapshotTracker == null){
 320             snapshotTracker = new SnapshotTracker(LOG, installSnapshot.getTotalChunks());
 321         }
 322
 323         updateInitialSyncStatus(installSnapshot.getLastIncludedIndex(), installSnapshot.getLeaderId());
 324
 325         try {
 326             if(snapshotTracker.addChunk(installSnapshot.getChunkIndex(), installSnapshot.getData(),
 327                     installSnapshot.getLastChunkHashCode())){
 328                 Snapshot snapshot = Snapshot.create(snapshotTracker.getSnapshot(),
 329                         new ArrayList<ReplicatedLogEntry>(),
 330                         installSnapshot.getLastIncludedIndex(),
 331                         installSnapshot.getLastIncludedTerm(),
 332                         installSnapshot.getLastIncludedIndex(),
 333                         installSnapshot.getLastIncludedTerm());
 334
 335                 actor().tell(new ApplySnapshot(snapshot), actor());
 336
 337                 snapshotTracker = null;
 338
 339             }
 340
 341             InstallSnapshotReply reply = new InstallSnapshotReply(
 342                     currentTerm(), context.getId(), installSnapshot.getChunkIndex(), true);
 343
 344             LOG.debug("{}: handleInstallSnapshot returning: {}", logName(), reply);
 345
 346             sender.tell(reply, actor());
 347
 348         } catch (SnapshotTracker.InvalidChunkException e) {
 349             LOG.debug("{}: Exception in InstallSnapshot of follower", logName(), e);
 350
 351             sender.tell(new InstallSnapshotReply(currentTerm(), context.getId(),
 352                     -1, false), actor());
 353             snapshotTracker = null;
 354
 355         } catch (Exception e){
 356             LOG.error("{}: Exception in InstallSnapshot of follower", logName(), e);
 357
 358             //send reply with success as false. The chunk will be sent again on failure
 359             sender.tell(new InstallSnapshotReply(currentTerm(), context.getId(),
 360                     installSnapshot.getChunkIndex(), false), actor());
 361
 362         }
 363     }
 364
 365     @Override
 366     public void close() throws Exception {
 367         stopElection();
 368     }
 369
 370     @VisibleForTesting
 371     SnapshotTracker getSnapshotTracker(){
 372         return snapshotTracker;
 373     }
 374
 375     private class InitialSyncStatusTracker {
 376
 377         private static final long INVALID_LOG_INDEX = -2L;
 378         private long initialLeaderCommit = INVALID_LOG_INDEX;
 379         private boolean initialSyncUpDone = false;
 380         private String syncedLeaderId = null;
 381         private final ActorRef actor;
 382
 383         public InitialSyncStatusTracker(ActorRef actor) {
 384             this.actor = actor;
 385         }
 386
 387         public void update(String leaderId, long leaderCommit, long commitIndex){
 388
 389             if(!leaderId.equals(syncedLeaderId)){
 390                 initialSyncUpDone = false;
 391                 initialLeaderCommit = INVALID_LOG_INDEX;
 392                 syncedLeaderId = leaderId;
 393             }
 394
 395             if(!initialSyncUpDone){
 396                 if(initialLeaderCommit == INVALID_LOG_INDEX){
 397                     actor.tell(new FollowerInitialSyncUpStatus(false, getId()), ActorRef.noSender());
 398                     initialLeaderCommit = leaderCommit;
 399                 } else if(commitIndex >= initialLeaderCommit){
 400                     actor.tell(new FollowerInitialSyncUpStatus(true, getId()), ActorRef.noSender());
 401                     initialSyncUpDone = true;
 402                 }
 403             }
 404         }
 405     }
 406 }