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