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