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