opendaylight/md-sal/sal-akka-raft/src/main/java/org/opendaylight/controller/cluster/raft/behaviors/Leader.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.actor.ActorSelection;
  13 import akka.actor.Cancellable;
  14 import com.google.common.base.Preconditions;
  15 import org.opendaylight.controller.cluster.raft.ClientRequestTracker;
  16 import org.opendaylight.controller.cluster.raft.ClientRequestTrackerImpl;
  17 import org.opendaylight.controller.cluster.raft.FollowerLogInformation;
  18 import org.opendaylight.controller.cluster.raft.FollowerLogInformationImpl;
  19 import org.opendaylight.controller.cluster.raft.RaftActorContext;
  20 import org.opendaylight.controller.cluster.raft.RaftState;
  21 import org.opendaylight.controller.cluster.raft.ReplicatedLogEntry;
  22 import org.opendaylight.controller.cluster.raft.internal.messages.ApplyState;
  23 import org.opendaylight.controller.cluster.raft.internal.messages.Replicate;
  24 import org.opendaylight.controller.cluster.raft.internal.messages.SendHeartBeat;
  25 import org.opendaylight.controller.cluster.raft.internal.messages.SendInstallSnapshot;
  26 import org.opendaylight.controller.cluster.raft.messages.AppendEntries;
  27 import org.opendaylight.controller.cluster.raft.messages.AppendEntriesReply;
  28 import org.opendaylight.controller.cluster.raft.messages.InstallSnapshot;
  29 import org.opendaylight.controller.cluster.raft.messages.InstallSnapshotReply;
  30 import org.opendaylight.controller.cluster.raft.messages.RaftRPC;
  31 import org.opendaylight.controller.cluster.raft.messages.RequestVoteReply;
  32 import scala.concurrent.duration.FiniteDuration;
  33
  34 import java.util.ArrayList;
  35 import java.util.Collections;
  36 import java.util.HashMap;
  37 import java.util.List;
  38 import java.util.Map;
  39 import java.util.concurrent.TimeUnit;
  40 import java.util.concurrent.atomic.AtomicLong;
  41
  42 /**
  43  * The behavior of a RaftActor when it is in the Leader state
  44  * <p/>
  45  * Leaders:
  46  * <ul>
  47  * <li> Upon election: send initial empty AppendEntries RPCs
  48  * (heartbeat) to each server; repeat during idle periods to
  49  * prevent election timeouts (§5.2)
  50  * <li> If command received from client: append entry to local log,
  51  * respond after entry applied to state machine (§5.3)
  52  * <li> If last log index ≥ nextIndex for a follower: send
  53  * AppendEntries RPC with log entries starting at nextIndex
  54  * <ul>
  55  * <li> If successful: update nextIndex and matchIndex for
  56  * follower (§5.3)
  57  * <li> If AppendEntries fails because of log inconsistency:
  58  * decrement nextIndex and retry (§5.3)
  59  * </ul>
  60  * <li> If there exists an N such that N > commitIndex, a majority
  61  * of matchIndex[i] ≥ N, and log[N].term == currentTerm:
  62  * set commitIndex = N (§5.3, §5.4).
  63  */
  64 public class Leader extends AbstractRaftActorBehavior {
  65
  66
  67     private final Map<String, FollowerLogInformation> followerToLog =
  68         new HashMap();
  69
  70     private final Map<String, ActorSelection> followerToActor = new HashMap<>();
  71
  72     private Cancellable heartbeatSchedule = null;
  73     private Cancellable appendEntriesSchedule = null;
  74     private Cancellable installSnapshotSchedule = null;
  75
  76     private List<ClientRequestTracker> trackerList = new ArrayList<>();
  77
  78     private final int minReplicationCount;
  79
  80     public Leader(RaftActorContext context) {
  81         super(context);
  82
  83         if (lastIndex() >= 0) {
  84             context.setCommitIndex(lastIndex());
  85         }
  86
  87         for (String followerId : context.getPeerAddresses().keySet()) {
  88             FollowerLogInformation followerLogInformation =
  89                 new FollowerLogInformationImpl(followerId,
  90                     new AtomicLong(lastIndex()),
  91                     new AtomicLong(-1));
  92
  93             followerToActor.put(followerId,
  94                 context.actorSelection(context.getPeerAddress(followerId)));
  95
  96             followerToLog.put(followerId, followerLogInformation);
  97         }
  98
  99         context.getLogger().debug("Election:Leader has following peers:"+followerToActor.keySet());
 100
 101         if (followerToActor.size() > 0) {
 102             minReplicationCount = (followerToActor.size() + 1) / 2 + 1;
 103         } else {
 104             minReplicationCount = 0;
 105         }
 106
 107
 108         // Immediately schedule a heartbeat
 109         // Upon election: send initial empty AppendEntries RPCs
 110         // (heartbeat) to each server; repeat during idle periods to
 111         // prevent election timeouts (§5.2)
 112         scheduleHeartBeat(new FiniteDuration(0, TimeUnit.SECONDS));
 113
 114         scheduleInstallSnapshotCheck(
 115             new FiniteDuration(HEART_BEAT_INTERVAL.length() * 1000,
 116                 HEART_BEAT_INTERVAL.unit())
 117         );
 118
 119     }
 120
 121     @Override protected RaftState handleAppendEntries(ActorRef sender,
 122         AppendEntries appendEntries) {
 123
 124         return state();
 125     }
 126
 127     @Override protected RaftState handleAppendEntriesReply(ActorRef sender,
 128         AppendEntriesReply appendEntriesReply) {
 129
 130         // Update the FollowerLogInformation
 131         String followerId = appendEntriesReply.getFollowerId();
 132         FollowerLogInformation followerLogInformation =
 133             followerToLog.get(followerId);
 134         if (appendEntriesReply.isSuccess()) {
 135             followerLogInformation
 136                 .setMatchIndex(appendEntriesReply.getLogLastIndex());
 137             followerLogInformation
 138                 .setNextIndex(appendEntriesReply.getLogLastIndex() + 1);
 139         } else {
 140
 141             // TODO: When we find that the follower is out of sync with the
 142             // Leader we simply decrement that followers next index by 1.
 143             // Would it be possible to do better than this? The RAFT spec
 144             // does not explicitly deal with it but may be something for us to
 145             // think about
 146
 147             followerLogInformation.decrNextIndex();
 148         }
 149
 150         // Now figure out if this reply warrants a change in the commitIndex
 151         // If there exists an N such that N > commitIndex, a majority
 152         // of matchIndex[i] ≥ N, and log[N].term == currentTerm:
 153         // set commitIndex = N (§5.3, §5.4).
 154         for (long N = context.getCommitIndex() + 1; ; N++) {
 155             int replicatedCount = 1;
 156
 157             for (FollowerLogInformation info : followerToLog.values()) {
 158                 if (info.getMatchIndex().get() >= N) {
 159                     replicatedCount++;
 160                 }
 161             }
 162
 163             if (replicatedCount >= minReplicationCount) {
 164                 ReplicatedLogEntry replicatedLogEntry =
 165                     context.getReplicatedLog().get(N);
 166                 if (replicatedLogEntry != null
 167                     && replicatedLogEntry.getTerm()
 168                     == currentTerm()) {
 169                     context.setCommitIndex(N);
 170                 }
 171             } else {
 172                 break;
 173             }
 174         }
 175
 176         // Apply the change to the state machine
 177         if (context.getCommitIndex() > context.getLastApplied()) {
 178             applyLogToStateMachine(context.getCommitIndex());
 179         }
 180
 181         return state();
 182     }
 183
 184     protected ClientRequestTracker findClientRequestTracker(long logIndex) {
 185         for (ClientRequestTracker tracker : trackerList) {
 186             if (tracker.getIndex() == logIndex) {
 187                 return tracker;
 188             }
 189         }
 190
 191         return null;
 192     }
 193
 194     @Override protected RaftState handleRequestVoteReply(ActorRef sender,
 195         RequestVoteReply requestVoteReply) {
 196         return state();
 197     }
 198
 199     @Override public RaftState state() {
 200         return RaftState.Leader;
 201     }
 202
 203     @Override public RaftState handleMessage(ActorRef sender, Object message) {
 204         Preconditions.checkNotNull(sender, "sender should not be null");
 205
 206         if (message instanceof RaftRPC) {
 207             RaftRPC rpc = (RaftRPC) message;
 208             // If RPC request or response contains term T > currentTerm:
 209             // set currentTerm = T, convert to follower (§5.1)
 210             // This applies to all RPC messages and responses
 211             if (rpc.getTerm() > context.getTermInformation().getCurrentTerm()) {
 212                 context.getTermInformation().updateAndPersist(rpc.getTerm(), null);
 213                 return RaftState.Follower;
 214             }
 215         }
 216
 217         try {
 218             if (message instanceof SendHeartBeat) {
 219                 return sendHeartBeat();
 220             } else if(message instanceof SendInstallSnapshot) {
 221                 installSnapshotIfNeeded();
 222             } else if (message instanceof Replicate) {
 223                 replicate((Replicate) message);
 224             } else if (message instanceof InstallSnapshotReply){
 225                 handleInstallSnapshotReply(
 226                     (InstallSnapshotReply) message);
 227             }
 228         } finally {
 229             scheduleHeartBeat(HEART_BEAT_INTERVAL);
 230         }
 231
 232         return super.handleMessage(sender, message);
 233     }
 234
 235     private void handleInstallSnapshotReply(InstallSnapshotReply message) {
 236         InstallSnapshotReply reply = message;
 237         String followerId = reply.getFollowerId();
 238         FollowerLogInformation followerLogInformation =
 239             followerToLog.get(followerId);
 240
 241         followerLogInformation
 242             .setMatchIndex(context.getReplicatedLog().getSnapshotIndex());
 243         followerLogInformation
 244             .setNextIndex(context.getReplicatedLog().getSnapshotIndex() + 1);
 245     }
 246
 247     private void replicate(Replicate replicate) {
 248         long logIndex = replicate.getReplicatedLogEntry().getIndex();
 249
 250         context.getLogger().debug("Replicate message " + logIndex);
 251
 252         if (followerToActor.size() == 0) {
 253             context.setCommitIndex(
 254                 replicate.getReplicatedLogEntry().getIndex());
 255
 256             context.getActor()
 257                 .tell(new ApplyState(replicate.getClientActor(),
 258                         replicate.getIdentifier(),
 259                         replicate.getReplicatedLogEntry()),
 260                     context.getActor()
 261                 );
 262         } else {
 263
 264             // Create a tracker entry we will use this later to notify the
 265             // client actor
 266             trackerList.add(
 267                 new ClientRequestTrackerImpl(replicate.getClientActor(),
 268                     replicate.getIdentifier(),
 269                     logIndex)
 270             );
 271
 272             sendAppendEntries();
 273         }
 274     }
 275
 276     private void sendAppendEntries() {
 277         // Send an AppendEntries to all followers
 278         for (String followerId : followerToActor.keySet()) {
 279             ActorSelection followerActor =
 280                 followerToActor.get(followerId);
 281
 282             FollowerLogInformation followerLogInformation =
 283                 followerToLog.get(followerId);
 284
 285             long nextIndex = followerLogInformation.getNextIndex().get();
 286
 287             List<ReplicatedLogEntry> entries = Collections.emptyList();
 288
 289             if(context.getReplicatedLog().isPresent(nextIndex)){
 290                 // TODO: Instead of sending all entries from nextIndex
 291                 // only send a fixed number of entries to each follower
 292                 // This is to avoid the situation where there are a lot of
 293                 // entries to install for a fresh follower or to a follower
 294                 // that has fallen too far behind with the log but yet is not
 295                 // eligible to receive a snapshot
 296                 entries =
 297                     context.getReplicatedLog().getFrom(nextIndex);
 298             }
 299
 300             followerActor.tell(
 301                 new AppendEntries(currentTerm(), context.getId(),
 302                     prevLogIndex(nextIndex), prevLogTerm(nextIndex),
 303                     entries, context.getCommitIndex()
 304                 ),
 305                 actor()
 306             );
 307         }
 308     }
 309
 310     /**
 311      * An installSnapshot is scheduled at a interval that is a multiple of
 312      * a HEARTBEAT_INTERVAL. This is to avoid the need to check for installing
 313      * snapshots at every heartbeat.
 314      */
 315     private void installSnapshotIfNeeded(){
 316         for (String followerId : followerToActor.keySet()) {
 317             ActorSelection followerActor =
 318                 followerToActor.get(followerId);
 319
 320             FollowerLogInformation followerLogInformation =
 321                 followerToLog.get(followerId);
 322
 323             long nextIndex = followerLogInformation.getNextIndex().get();
 324
 325             if(!context.getReplicatedLog().isPresent(nextIndex) && context.getReplicatedLog().isInSnapshot(nextIndex)){
 326                 followerActor.tell(
 327                     new InstallSnapshot(currentTerm(), context.getId(),
 328                         context.getReplicatedLog().getSnapshotIndex(),
 329                         context.getReplicatedLog().getSnapshotTerm(),
 330                         context.getReplicatedLog().getSnapshot()
 331                     ),
 332                     actor()
 333                 );
 334             }
 335         }
 336     }
 337
 338     private RaftState sendHeartBeat() {
 339         if (followerToActor.size() > 0) {
 340             sendAppendEntries();
 341         }
 342         return state();
 343     }
 344
 345     private void stopHeartBeat() {
 346         if (heartbeatSchedule != null && !heartbeatSchedule.isCancelled()) {
 347             heartbeatSchedule.cancel();
 348         }
 349     }
 350
 351     private void stopInstallSnapshotSchedule() {
 352         if (installSnapshotSchedule != null && !installSnapshotSchedule.isCancelled()) {
 353             installSnapshotSchedule.cancel();
 354         }
 355     }
 356
 357     private void scheduleHeartBeat(FiniteDuration interval) {
 358         if(followerToActor.keySet().size() == 0){
 359             // Optimization - do not bother scheduling a heartbeat as there are
 360             // no followers
 361             return;
 362         }
 363
 364         stopHeartBeat();
 365
 366         // Schedule a heartbeat. When the scheduler triggers a SendHeartbeat
 367         // message is sent to itself.
 368         // Scheduling the heartbeat only once here because heartbeats do not
 369         // need to be sent if there are other messages being sent to the remote
 370         // actor.
 371         heartbeatSchedule =
 372             context.getActorSystem().scheduler().scheduleOnce(
 373                 interval,
 374                 context.getActor(), new SendHeartBeat(),
 375                 context.getActorSystem().dispatcher(), context.getActor());
 376     }
 377
 378
 379     private void scheduleInstallSnapshotCheck(FiniteDuration interval) {
 380         if(followerToActor.keySet().size() == 0){
 381             // Optimization - do not bother scheduling a heartbeat as there are
 382             // no followers
 383             return;
 384         }
 385
 386         stopInstallSnapshotSchedule();
 387
 388         // Schedule a message to send append entries to followers that can
 389         // accept an append entries with some data in it
 390         installSnapshotSchedule =
 391             context.getActorSystem().scheduler().scheduleOnce(
 392                 interval,
 393                 context.getActor(), new SendInstallSnapshot(),
 394                 context.getActorSystem().dispatcher(), context.getActor());
 395     }
 396
 397
 398
 399     @Override public void close() throws Exception {
 400         stopHeartBeat();
 401     }
 402
 403     @Override public String getLeaderId() {
 404         return context.getId();
 405     }
 406
 407 }