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 akka.event.LoggingAdapter;
  13 import com.google.protobuf.ByteString;
  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.messages.AppendEntries;
  21 import org.opendaylight.controller.cluster.raft.messages.AppendEntriesReply;
  22 import org.opendaylight.controller.cluster.raft.messages.InstallSnapshot;
  23 import org.opendaylight.controller.cluster.raft.messages.InstallSnapshotReply;
  24 import org.opendaylight.controller.cluster.raft.messages.RaftRPC;
  25 import org.opendaylight.controller.cluster.raft.messages.RequestVoteReply;
  26
  27 import java.util.ArrayList;
  28
  29 /**
  30  * The behavior of a RaftActor in the Follower state
  31  * <p/>
  32  * <ul>
  33  * <li> Respond to RPCs from candidates and leaders
  34  * <li> If election timeout elapses without receiving AppendEntries
  35  * RPC from current leader or granting vote to candidate:
  36  * convert to candidate
  37  * </ul>
  38  */
  39 public class Follower extends AbstractRaftActorBehavior {
  40     private ByteString snapshotChunksCollected = ByteString.EMPTY;
  41
  42     private final LoggingAdapter LOG;
  43
  44     public Follower(RaftActorContext context) {
  45         super(context);
  46
  47         LOG = context.getLogger();
  48
  49         scheduleElection(electionDuration());
  50     }
  51
  52     @Override protected RaftState handleAppendEntries(ActorRef sender,
  53         AppendEntries appendEntries) {
  54
  55         if(appendEntries.getEntries() != null && appendEntries.getEntries().size() > 0) {
  56             if(LOG.isDebugEnabled()) {
  57                 LOG.debug(appendEntries.toString());
  58             }
  59         }
  60
  61         // TODO : Refactor this method into a bunch of smaller methods
  62         // to make it easier to read. Before refactoring ensure tests
  63         // cover the code properly
  64
  65         // 1. Reply false if term < currentTerm (§5.1)
  66         // This is handled in the appendEntries method of the base class
  67
  68         // If we got here then we do appear to be talking to the leader
  69         leaderId = appendEntries.getLeaderId();
  70
  71         // 2. Reply false if log doesn’t contain an entry at prevLogIndex
  72         // whose term matches prevLogTerm (§5.3)
  73
  74         ReplicatedLogEntry previousEntry = context.getReplicatedLog()
  75             .get(appendEntries.getPrevLogIndex());
  76
  77
  78         boolean outOfSync = true;
  79
  80         // First check if the logs are in sync or not
  81         if (lastIndex() == -1
  82             && appendEntries.getPrevLogIndex() != -1) {
  83
  84             // The follower's log is out of sync because the leader does have
  85             // an entry at prevLogIndex and this follower has no entries in
  86             // it's log.
  87
  88             if(LOG.isDebugEnabled()) {
  89                 LOG.debug("The followers log is empty and the senders prevLogIndex is {}",
  90                     appendEntries.getPrevLogIndex());
  91             }
  92
  93         } else if (lastIndex() > -1
  94             && appendEntries.getPrevLogIndex() != -1
  95             && previousEntry == null) {
  96
  97             // The follower's log is out of sync because the Leader's
  98             // prevLogIndex entry was not found in it's log
  99
 100             if(LOG.isDebugEnabled()) {
 101                 LOG.debug("The log is not empty but the prevLogIndex {} was not found in it",
 102                     appendEntries.getPrevLogIndex());
 103             }
 104
 105         } else if (lastIndex() > -1
 106             && previousEntry != null
 107             && previousEntry.getTerm()!= appendEntries.getPrevLogTerm()) {
 108
 109             // The follower's log is out of sync because the Leader's
 110             // prevLogIndex entry does exist in the follower's log but it has
 111             // a different term in it
 112
 113             if(LOG.isDebugEnabled()) {
 114                 LOG.debug(
 115                     "Cannot append entries because previous entry term {}  is not equal to append entries prevLogTerm {}"
 116                     , previousEntry.getTerm()
 117                     , appendEntries.getPrevLogTerm());
 118             }
 119         } else {
 120             outOfSync = false;
 121         }
 122
 123         if (outOfSync) {
 124             // We found that the log was out of sync so just send a negative
 125             // reply and return
 126             if(LOG.isDebugEnabled()) {
 127                 LOG.debug("Follower is out-of-sync, " +
 128                         "so sending negative reply, lastIndex():{}, lastTerm():{}",
 129                     lastIndex(), lastTerm()
 130                 );
 131             }
 132             sender.tell(
 133                 new AppendEntriesReply(context.getId(), currentTerm(), false,
 134                     lastIndex(), lastTerm()), actor()
 135             );
 136             return state();
 137         }
 138
 139         if (appendEntries.getEntries() != null
 140             && appendEntries.getEntries().size() > 0) {
 141             if(LOG.isDebugEnabled()) {
 142                 LOG.debug(
 143                     "Number of entries to be appended = " + appendEntries
 144                         .getEntries().size()
 145                 );
 146             }
 147
 148             // 3. If an existing entry conflicts with a new one (same index
 149             // but different terms), delete the existing entry and all that
 150             // follow it (§5.3)
 151             int addEntriesFrom = 0;
 152             if (context.getReplicatedLog().size() > 0) {
 153
 154                 // Find the entry up until which the one that is not in the follower's log
 155                 for (int i = 0;i < appendEntries.getEntries().size(); i++, addEntriesFrom++) {
 156                     ReplicatedLogEntry matchEntry = appendEntries.getEntries().get(i);
 157                     ReplicatedLogEntry newEntry = context.getReplicatedLog().get(matchEntry.getIndex());
 158
 159                     if (newEntry == null) {
 160                         //newEntry not found in the log
 161                         break;
 162                     }
 163
 164                     if (newEntry.getTerm() == matchEntry
 165                         .getTerm()) {
 166                         continue;
 167                     }
 168
 169                     if(LOG.isDebugEnabled()) {
 170                         LOG.debug(
 171                             "Removing entries from log starting at "
 172                                 + matchEntry.getIndex()
 173                         );
 174                     }
 175
 176                     // Entries do not match so remove all subsequent entries
 177                     context.getReplicatedLog()
 178                         .removeFromAndPersist(matchEntry.getIndex());
 179                     break;
 180                 }
 181             }
 182
 183             if(LOG.isDebugEnabled()) {
 184                 context.getLogger().debug(
 185                     "After cleanup entries to be added from = " + (addEntriesFrom
 186                         + lastIndex())
 187                 );
 188             }
 189
 190             // 4. Append any new entries not already in the log
 191             for (int i = addEntriesFrom;
 192                  i < appendEntries.getEntries().size(); i++) {
 193
 194                 context.getLogger().info(
 195                     "Append entry to log " + appendEntries.getEntries().get(
 196                         i).getData()
 197                         .toString()
 198                 );
 199                 context.getReplicatedLog()
 200                     .appendAndPersist(appendEntries.getEntries().get(i));
 201             }
 202
 203             if(LOG.isDebugEnabled()) {
 204                 LOG.debug("Log size is now " + context.getReplicatedLog().size());
 205             }
 206         }
 207
 208
 209         // 5. If leaderCommit > commitIndex, set commitIndex =
 210         // min(leaderCommit, index of last new entry)
 211
 212         long prevCommitIndex = context.getCommitIndex();
 213
 214         context.setCommitIndex(Math.min(appendEntries.getLeaderCommit(),
 215             context.getReplicatedLog().lastIndex()));
 216
 217         if (prevCommitIndex != context.getCommitIndex()) {
 218             if(LOG.isDebugEnabled()) {
 219                 LOG.debug("Commit index set to " + context.getCommitIndex());
 220             }
 221         }
 222
 223         // If commitIndex > lastApplied: increment lastApplied, apply
 224         // log[lastApplied] to state machine (§5.3)
 225         // check if there are any entries to be applied. last-applied can be equal to last-index
 226         if (appendEntries.getLeaderCommit() > context.getLastApplied() &&
 227             context.getLastApplied() < lastIndex()) {
 228             if(LOG.isDebugEnabled()) {
 229                 LOG.debug("applyLogToStateMachine, " +
 230                         "appendEntries.getLeaderCommit():{}," +
 231                         "context.getLastApplied():{}, lastIndex():{}",
 232                     appendEntries.getLeaderCommit(), context.getLastApplied(), lastIndex()
 233                 );
 234             }
 235
 236             applyLogToStateMachine(appendEntries.getLeaderCommit());
 237         }
 238
 239         sender.tell(new AppendEntriesReply(context.getId(), currentTerm(), true,
 240             lastIndex(), lastTerm()), actor());
 241
 242         return state();
 243     }
 244
 245     @Override protected RaftState handleAppendEntriesReply(ActorRef sender,
 246         AppendEntriesReply appendEntriesReply) {
 247         return state();
 248     }
 249
 250     @Override protected RaftState handleRequestVoteReply(ActorRef sender,
 251         RequestVoteReply requestVoteReply) {
 252         return state();
 253     }
 254
 255     @Override public RaftState state() {
 256         return RaftState.Follower;
 257     }
 258
 259     @Override public RaftState handleMessage(ActorRef sender, Object originalMessage) {
 260
 261         Object message = fromSerializableMessage(originalMessage);
 262
 263         if (message instanceof RaftRPC) {
 264             RaftRPC rpc = (RaftRPC) message;
 265             // If RPC request or response contains term T > currentTerm:
 266             // set currentTerm = T, convert to follower (§5.1)
 267             // This applies to all RPC messages and responses
 268             if (rpc.getTerm() > context.getTermInformation().getCurrentTerm()) {
 269                 context.getTermInformation().updateAndPersist(rpc.getTerm(), null);
 270             }
 271         }
 272
 273         if (message instanceof ElectionTimeout) {
 274             return RaftState.Candidate;
 275
 276         } else if (message instanceof InstallSnapshot) {
 277             InstallSnapshot installSnapshot = (InstallSnapshot) message;
 278             handleInstallSnapshot(sender, installSnapshot);
 279         }
 280
 281         scheduleElection(electionDuration());
 282
 283         return super.handleMessage(sender, message);
 284     }
 285
 286     private void handleInstallSnapshot(ActorRef sender, InstallSnapshot installSnapshot) {
 287
 288         if(LOG.isDebugEnabled()) {
 289             LOG.debug("InstallSnapshot received by follower " +
 290                     "datasize:{} , Chunk:{}/{}", installSnapshot.getData().size(),
 291                 installSnapshot.getChunkIndex(), installSnapshot.getTotalChunks()
 292             );
 293         }
 294
 295         try {
 296             if (installSnapshot.getChunkIndex() == installSnapshot.getTotalChunks()) {
 297                 // this is the last chunk, create a snapshot object and apply
 298
 299                 snapshotChunksCollected = snapshotChunksCollected.concat(installSnapshot.getData());
 300                 context.getLogger().debug("Last chunk received: snapshotChunksCollected.size:{}",
 301                     snapshotChunksCollected.size());
 302
 303                 Snapshot snapshot = Snapshot.create(snapshotChunksCollected.toByteArray(),
 304                     new ArrayList<ReplicatedLogEntry>(),
 305                     installSnapshot.getLastIncludedIndex(),
 306                     installSnapshot.getLastIncludedTerm(),
 307                     installSnapshot.getLastIncludedIndex(),
 308                     installSnapshot.getLastIncludedTerm());
 309
 310                 actor().tell(new ApplySnapshot(snapshot), actor());
 311
 312             } else {
 313                 // we have more to go
 314                 snapshotChunksCollected = snapshotChunksCollected.concat(installSnapshot.getData());
 315
 316                 if(LOG.isDebugEnabled()) {
 317                     LOG.debug("Chunk={},snapshotChunksCollected.size:{}",
 318                         installSnapshot.getChunkIndex(), snapshotChunksCollected.size());
 319                 }
 320             }
 321
 322             sender.tell(new InstallSnapshotReply(
 323                 currentTerm(), context.getId(), installSnapshot.getChunkIndex(),
 324                 true), actor());
 325
 326         } catch (Exception e) {
 327             context.getLogger().error("Exception in InstallSnapshot of follower", e);
 328             //send reply with success as false. The chunk will be sent again on failure
 329             sender.tell(new InstallSnapshotReply(currentTerm(), context.getId(),
 330                 installSnapshot.getChunkIndex(), false), actor());
 331         }
 332     }
 333
 334     @Override public void close() throws Exception {
 335         stopElection();
 336     }
 337 }