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