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.getRaftPolicy().automaticElectionsEnabled()) {
  52             if (context.getPeerAddresses().isEmpty()) {
  53                 actor().tell(ELECTION_TIMEOUT, actor());
  54             } else {
  55                 scheduleElection(electionDuration());
  56             }
  57         }
  58
  59     }
  60
  61     private boolean isLogEntryPresent(long index){
  62         if(index == context.getReplicatedLog().getSnapshotIndex()){
  63             return true;
  64         }
  65
  66         ReplicatedLogEntry previousEntry = context.getReplicatedLog()
  67                 .get(index);
  68
  69         return previousEntry != null;
  70
  71     }
  72
  73     private long getLogEntryTerm(long index){
  74         if(index == context.getReplicatedLog().getSnapshotIndex()){
  75             return context.getReplicatedLog().getSnapshotTerm();
  76         }
  77
  78         ReplicatedLogEntry previousEntry = context.getReplicatedLog()
  79                 .get(index);
  80
  81         if(previousEntry != null){
  82             return previousEntry.getTerm();
  83         }
  84
  85         return -1;
  86     }
  87
  88     private void updateInitialSyncStatus(long currentLeaderCommit, String leaderId){
  89         initialSyncStatusTracker.update(leaderId, currentLeaderCommit, context.getCommitIndex());
  90     }
  91
  92     @Override protected RaftActorBehavior handleAppendEntries(ActorRef sender,
  93                                                               AppendEntries appendEntries) {
  94
  95         int numLogEntries = appendEntries.getEntries() != null ? appendEntries.getEntries().size() : 0;
  96         if(LOG.isTraceEnabled()) {
  97             LOG.trace("{}: handleAppendEntries: {}", logName(), appendEntries);
  98         } else if(LOG.isDebugEnabled() && numLogEntries > 0) {
  99             LOG.debug("{}: handleAppendEntries: {}", logName(), appendEntries);
 100         }
 101
 102         // TODO : Refactor this method into a bunch of smaller methods
 103         // to make it easier to read. Before refactoring ensure tests
 104         // cover the code properly
 105
 106         if (snapshotTracker != null) {
 107             // if snapshot install is in progress, follower should just acknowledge append entries with a reply.
 108             AppendEntriesReply reply = new AppendEntriesReply(context.getId(), currentTerm(), true,
 109                     lastIndex(), lastTerm(), context.getPayloadVersion());
 110
 111             if(LOG.isDebugEnabled()) {
 112                 LOG.debug("{}: snapshot install is in progress, replying immediately with {}", logName(), reply);
 113             }
 114             sender.tell(reply, actor());
 115
 116             return this;
 117         }
 118
 119         // 1. Reply false if term < currentTerm (§5.1)
 120         // This is handled in the appendEntries method of the base class
 121
 122         // If we got here then we do appear to be talking to the leader
 123         leaderId = appendEntries.getLeaderId();
 124
 125         setLeaderPayloadVersion(appendEntries.getPayloadVersion());
 126
 127         // 2. Reply false if log doesn’t contain an entry at prevLogIndex
 128         // whose term matches prevLogTerm (§5.3)
 129
 130         long prevLogTerm = getLogEntryTerm(appendEntries.getPrevLogIndex());
 131         boolean prevEntryPresent = isLogEntryPresent(appendEntries.getPrevLogIndex());
 132
 133         updateInitialSyncStatus(appendEntries.getLeaderCommit(), appendEntries.getLeaderId());
 134
 135         boolean outOfSync = true;
 136
 137         // First check if the logs are in sync or not
 138         long lastIndex = lastIndex();
 139         if (lastIndex == -1 && appendEntries.getPrevLogIndex() != -1) {
 140
 141             // The follower's log is out of sync because the leader does have
 142             // an entry at prevLogIndex and this follower has no entries in
 143             // it's log.
 144
 145             LOG.debug("{}: The followers log is empty and the senders prevLogIndex is {}",
 146                         logName(), appendEntries.getPrevLogIndex());
 147         } else if (lastIndex > -1 && appendEntries.getPrevLogIndex() != -1 && !prevEntryPresent) {
 148
 149             // The follower's log is out of sync because the Leader's
 150             // prevLogIndex entry was not found in it's log
 151
 152             LOG.debug("{}: The log is not empty but the prevLogIndex {} was not found in it",
 153                         logName(), appendEntries.getPrevLogIndex());
 154         } else if (lastIndex > -1 && prevEntryPresent && prevLogTerm != appendEntries.getPrevLogTerm()) {
 155
 156             // The follower's log is out of sync because the Leader's
 157             // prevLogIndex entry does exist in the follower's log but it has
 158             // a different term in it
 159
 160             LOG.debug(
 161                 "{}: Cannot append entries because previous entry term {}  is not equal to append entries prevLogTerm {}",
 162                  logName(), prevLogTerm, appendEntries.getPrevLogTerm());
 163         } else {
 164             outOfSync = false;
 165         }
 166
 167         if (outOfSync) {
 168             // We found that the log was out of sync so just send a negative
 169             // reply and return
 170
 171             LOG.debug("{}: Follower is out-of-sync, so sending negative reply, lastIndex: {}, lastTerm: {}",
 172                         logName(), lastIndex, lastTerm());
 173
 174             sender.tell(new AppendEntriesReply(context.getId(), currentTerm(), false, lastIndex,
 175                     lastTerm(), context.getPayloadVersion()), actor());
 176             return this;
 177         }
 178
 179         if (appendEntries.getEntries() != null && appendEntries.getEntries().size() > 0) {
 180
 181             LOG.debug("{}: Number of entries to be appended = {}", logName(),
 182                         appendEntries.getEntries().size());
 183
 184             // 3. If an existing entry conflicts with a new one (same index
 185             // but different terms), delete the existing entry and all that
 186             // follow it (§5.3)
 187             int addEntriesFrom = 0;
 188             if (context.getReplicatedLog().size() > 0) {
 189
 190                 // Find the entry up until which the one that is not in the follower's log
 191                 for (int i = 0;i < appendEntries.getEntries().size(); i++, addEntriesFrom++) {
 192                     ReplicatedLogEntry matchEntry = appendEntries.getEntries().get(i);
 193                     ReplicatedLogEntry newEntry = context.getReplicatedLog().get(matchEntry.getIndex());
 194
 195                     if (newEntry == null) {
 196                         //newEntry not found in the log
 197                         break;
 198                     }
 199
 200                     if (newEntry.getTerm() == matchEntry.getTerm()) {
 201                         continue;
 202                     }
 203
 204                     LOG.debug("{}: Removing entries from log starting at {}", logName(),
 205                                 matchEntry.getIndex());
 206
 207                     // Entries do not match so remove all subsequent entries
 208                     context.getReplicatedLog().removeFromAndPersist(matchEntry.getIndex());
 209                     break;
 210                 }
 211             }
 212
 213             lastIndex = lastIndex();
 214             LOG.debug("{}: After cleanup entries to be added from = {}", logName(),
 215                         (addEntriesFrom + lastIndex));
 216
 217             // 4. Append any new entries not already in the log
 218             for (int i = addEntriesFrom; i < appendEntries.getEntries().size(); i++) {
 219                 ReplicatedLogEntry entry = appendEntries.getEntries().get(i);
 220
 221                 LOG.debug("{}: Append entry to log {}", logName(), entry.getData());
 222
 223                 context.getReplicatedLog().appendAndPersist(entry);
 224             }
 225
 226             LOG.debug("{}: Log size is now {}", logName(), context.getReplicatedLog().size());
 227         }
 228
 229         // 5. If leaderCommit > commitIndex, set commitIndex =
 230         // min(leaderCommit, index of last new entry)
 231
 232         lastIndex = lastIndex();
 233         long prevCommitIndex = context.getCommitIndex();
 234
 235         context.setCommitIndex(Math.min(appendEntries.getLeaderCommit(), lastIndex));
 236
 237         if (prevCommitIndex != context.getCommitIndex()) {
 238             LOG.debug("{}: Commit index set to {}", logName(), context.getCommitIndex());
 239         }
 240
 241         // If commitIndex > lastApplied: increment lastApplied, apply
 242         // log[lastApplied] to state machine (§5.3)
 243         // check if there are any entries to be applied. last-applied can be equal to last-index
 244         if (appendEntries.getLeaderCommit() > context.getLastApplied() &&
 245             context.getLastApplied() < lastIndex) {
 246             if(LOG.isDebugEnabled()) {
 247                 LOG.debug("{}: applyLogToStateMachine, " +
 248                         "appendEntries.getLeaderCommit(): {}," +
 249                         "context.getLastApplied(): {}, lastIndex(): {}", logName(),
 250                     appendEntries.getLeaderCommit(), context.getLastApplied(), lastIndex);
 251             }
 252
 253             applyLogToStateMachine(appendEntries.getLeaderCommit());
 254         }
 255
 256         AppendEntriesReply reply = new AppendEntriesReply(context.getId(), currentTerm(), true,
 257             lastIndex, lastTerm(), context.getPayloadVersion());
 258
 259         if(LOG.isTraceEnabled()) {
 260             LOG.trace("{}: handleAppendEntries returning : {}", logName(), reply);
 261         } else if(LOG.isDebugEnabled() && numLogEntries > 0) {
 262             LOG.debug("{}: handleAppendEntries returning : {}", logName(), reply);
 263         }
 264
 265         sender.tell(reply, actor());
 266
 267         if (!context.getSnapshotManager().isCapturing()) {
 268             super.performSnapshotWithoutCapture(appendEntries.getReplicatedToAllIndex());
 269         }
 270
 271         return this;
 272     }
 273
 274     @Override protected RaftActorBehavior handleAppendEntriesReply(ActorRef sender,
 275         AppendEntriesReply appendEntriesReply) {
 276         return this;
 277     }
 278
 279     @Override protected RaftActorBehavior handleRequestVoteReply(ActorRef sender,
 280         RequestVoteReply requestVoteReply) {
 281         return this;
 282     }
 283
 284     @Override public RaftActorBehavior handleMessage(ActorRef sender, Object originalMessage) {
 285
 286         Object message = fromSerializableMessage(originalMessage);
 287
 288         if (message instanceof RaftRPC) {
 289             RaftRPC rpc = (RaftRPC) message;
 290             // If RPC request or response contains term T > currentTerm:
 291             // set currentTerm = T, convert to follower (§5.1)
 292             // This applies to all RPC messages and responses
 293             if (rpc.getTerm() > context.getTermInformation().getCurrentTerm()) {
 294                 LOG.debug("{}: Term {} in \"{}\" message is greater than follower's term {} - updating term",
 295                         logName(), rpc.getTerm(), rpc, context.getTermInformation().getCurrentTerm());
 296
 297                 context.getTermInformation().updateAndPersist(rpc.getTerm(), null);
 298             }
 299         }
 300
 301         if (message instanceof ElectionTimeout) {
 302             LOG.debug("{}: Received ElectionTimeout - switching to Candidate", logName());
 303             return switchBehavior(new Candidate(context));
 304
 305         } else if (message instanceof InstallSnapshot) {
 306             InstallSnapshot installSnapshot = (InstallSnapshot) message;
 307             handleInstallSnapshot(sender, installSnapshot);
 308         }
 309
 310         scheduleElection(electionDuration());
 311
 312         return super.handleMessage(sender, message);
 313     }
 314
 315     private void handleInstallSnapshot(ActorRef sender, InstallSnapshot installSnapshot) {
 316
 317         LOG.debug("{}: InstallSnapshot received from leader {}, datasize: {} , Chunk: {}/{}",
 318                     logName(), installSnapshot.getLeaderId(), installSnapshot.getData().size(),
 319                     installSnapshot.getChunkIndex(), installSnapshot.getTotalChunks());
 320
 321         if(snapshotTracker == null){
 322             snapshotTracker = new SnapshotTracker(LOG, installSnapshot.getTotalChunks());
 323         }
 324
 325         updateInitialSyncStatus(installSnapshot.getLastIncludedIndex(), installSnapshot.getLeaderId());
 326
 327         try {
 328             if(snapshotTracker.addChunk(installSnapshot.getChunkIndex(), installSnapshot.getData(),
 329                     installSnapshot.getLastChunkHashCode())){
 330                 Snapshot snapshot = Snapshot.create(snapshotTracker.getSnapshot(),
 331                         new ArrayList<ReplicatedLogEntry>(),
 332                         installSnapshot.getLastIncludedIndex(),
 333                         installSnapshot.getLastIncludedTerm(),
 334                         installSnapshot.getLastIncludedIndex(),
 335                         installSnapshot.getLastIncludedTerm());
 336
 337                 actor().tell(new ApplySnapshot(snapshot), actor());
 338
 339                 snapshotTracker = null;
 340
 341             }
 342
 343             InstallSnapshotReply reply = new InstallSnapshotReply(
 344                     currentTerm(), context.getId(), installSnapshot.getChunkIndex(), true);
 345
 346             LOG.debug("{}: handleInstallSnapshot returning: {}", logName(), reply);
 347
 348             sender.tell(reply, actor());
 349
 350         } catch (SnapshotTracker.InvalidChunkException e) {
 351             LOG.debug("{}: Exception in InstallSnapshot of follower", logName(), e);
 352
 353             sender.tell(new InstallSnapshotReply(currentTerm(), context.getId(),
 354                     -1, false), actor());
 355             snapshotTracker = null;
 356
 357         } catch (Exception e){
 358             LOG.error("{}: Exception in InstallSnapshot of follower", logName(), e);
 359
 360             //send reply with success as false. The chunk will be sent again on failure
 361             sender.tell(new InstallSnapshotReply(currentTerm(), context.getId(),
 362                     installSnapshot.getChunkIndex(), false), actor());
 363
 364         }
 365     }
 366
 367     @Override
 368     public void close() throws Exception {
 369         stopElection();
 370     }
 371
 372     @VisibleForTesting
 373     SnapshotTracker getSnapshotTracker(){
 374         return snapshotTracker;
 375     }
 376
 377     private class InitialSyncStatusTracker {
 378
 379         private static final long INVALID_LOG_INDEX = -2L;
 380         private long initialLeaderCommit = INVALID_LOG_INDEX;
 381         private boolean initialSyncUpDone = false;
 382         private String syncedLeaderId = null;
 383         private final ActorRef actor;
 384
 385         public InitialSyncStatusTracker(ActorRef actor) {
 386             this.actor = actor;
 387         }
 388
 389         public void update(String leaderId, long leaderCommit, long commitIndex){
 390
 391             if(!leaderId.equals(syncedLeaderId)){
 392                 initialSyncUpDone = false;
 393                 initialLeaderCommit = INVALID_LOG_INDEX;
 394                 syncedLeaderId = leaderId;
 395             }
 396
 397             if(!initialSyncUpDone){
 398                 if(initialLeaderCommit == INVALID_LOG_INDEX){
 399                     actor.tell(new FollowerInitialSyncUpStatus(false, getId()), ActorRef.noSender());
 400                     initialLeaderCommit = leaderCommit;
 401                 } else if(commitIndex >= initialLeaderCommit){
 402                     actor.tell(new FollowerInitialSyncUpStatus(true, getId()), ActorRef.noSender());
 403                     initialSyncUpDone = true;
 404                 }
 405             }
 406         }
 407     }
 408 }