2 * Copyright (c) 2014 Cisco Systems, Inc. and others. All rights reserved.
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
9 package org.opendaylight.controller.cluster.raft;
11 import akka.actor.ActorRef;
12 import akka.actor.ActorSelection;
13 import akka.event.Logging;
14 import akka.event.LoggingAdapter;
15 import akka.japi.Procedure;
16 import akka.persistence.RecoveryCompleted;
17 import akka.persistence.SaveSnapshotFailure;
18 import akka.persistence.SaveSnapshotSuccess;
19 import akka.persistence.SnapshotOffer;
20 import akka.persistence.SnapshotSelectionCriteria;
21 import akka.persistence.UntypedPersistentActor;
22 import org.opendaylight.controller.cluster.raft.base.messages.ApplySnapshot;
23 import org.opendaylight.controller.cluster.raft.base.messages.ApplyState;
24 import org.opendaylight.controller.cluster.raft.base.messages.Replicate;
25 import org.opendaylight.controller.cluster.raft.behaviors.Candidate;
26 import org.opendaylight.controller.cluster.raft.behaviors.Follower;
27 import org.opendaylight.controller.cluster.raft.behaviors.Leader;
28 import org.opendaylight.controller.cluster.raft.behaviors.RaftActorBehavior;
29 import org.opendaylight.controller.cluster.raft.client.messages.AddRaftPeer;
30 import org.opendaylight.controller.cluster.raft.client.messages.FindLeader;
31 import org.opendaylight.controller.cluster.raft.client.messages.FindLeaderReply;
32 import org.opendaylight.controller.cluster.raft.client.messages.RemoveRaftPeer;
33 import org.opendaylight.controller.cluster.raft.protobuff.client.messages.Payload;
35 import java.io.Serializable;
36 import java.util.ArrayList;
37 import java.util.List;
41 * RaftActor encapsulates a state machine that needs to be kept synchronized
42 * in a cluster. It implements the RAFT algorithm as described in the paper
43 * <a href='https://ramcloud.stanford.edu/wiki/download/attachments/11370504/raft.pdf'>
44 * In Search of an Understandable Consensus Algorithm</a>
46 * RaftActor has 3 states and each state has a certain behavior associated
47 * with it. A Raft actor can behave as,
50 * <li> A Follower (or) </li>
51 * <li> A Candidate </li>
55 * A RaftActor MUST be a Leader in order to accept requests from clients to
56 * change the state of it's encapsulated state machine. Once a RaftActor becomes
57 * a Leader it is also responsible for ensuring that all followers ultimately
58 * have the same log and therefore the same state machine as itself.
61 * The current behavior of a RaftActor determines how election for leadership
62 * is initiated and how peer RaftActors react to request for votes.
65 * Each RaftActor also needs to know the current election term. It uses this
66 * information for a couple of things. One is to simply figure out who it
67 * voted for in the last election. Another is to figure out if the message
68 * it received to update it's state is stale.
71 * The RaftActor uses akka-persistence to store it's replicated log.
72 * Furthermore through it's behaviors a Raft Actor determines
75 * <li> when a log entry should be persisted </li>
76 * <li> when a log entry should be applied to the state machine (and) </li>
77 * <li> when a snapshot should be saved </li>
80 public abstract class RaftActor extends UntypedPersistentActor {
81 protected final LoggingAdapter LOG =
82 Logging.getLogger(getContext().system(), this);
85 * The current state determines the current behavior of a RaftActor
86 * A Raft Actor always starts off in the Follower State
88 private RaftActorBehavior currentBehavior;
91 * This context should NOT be passed directly to any other actor it is
92 * only to be consumed by the RaftActorBehaviors
94 private RaftActorContext context;
97 * The in-memory journal
99 private ReplicatedLogImpl replicatedLog = new ReplicatedLogImpl();
102 public RaftActor(String id, Map<String, String> peerAddresses) {
103 context = new RaftActorContextImpl(this.getSelf(),
105 id, new ElectionTermImpl(),
106 -1, -1, replicatedLog, peerAddresses, LOG);
109 @Override public void onReceiveRecover(Object message) {
110 if (message instanceof SnapshotOffer) {
111 SnapshotOffer offer = (SnapshotOffer) message;
112 Snapshot snapshot = (Snapshot) offer.snapshot();
114 // Create a replicated log with the snapshot information
115 // The replicated log can be used later on to retrieve this snapshot
116 // when we need to install it on a peer
117 replicatedLog = new ReplicatedLogImpl(snapshot);
119 // Apply the snapshot to the actors state
120 applySnapshot(snapshot.getState());
122 } else if (message instanceof ReplicatedLogEntry) {
123 replicatedLog.append((ReplicatedLogEntry) message);
124 } else if (message instanceof DeleteEntries) {
125 replicatedLog.removeFrom(((DeleteEntries) message).getFromIndex());
126 } else if (message instanceof UpdateElectionTerm) {
127 context.getTermInformation().update(((UpdateElectionTerm) message).getCurrentTerm(), ((UpdateElectionTerm) message).getVotedFor());
128 } else if (message instanceof RecoveryCompleted) {
130 "Last index in log : " + replicatedLog.lastIndex());
131 currentBehavior = switchBehavior(RaftState.Follower);
135 @Override public void onReceiveCommand(Object message) {
136 if (message instanceof ApplyState){
137 ApplyState applyState = (ApplyState) message;
139 LOG.debug("Applying state for log index {} data {}",
140 applyState.getReplicatedLogEntry().getIndex(),
141 applyState.getReplicatedLogEntry().getData());
143 applyState(applyState.getClientActor(), applyState.getIdentifier(),
144 applyState.getReplicatedLogEntry().getData());
146 } else if(message instanceof ApplySnapshot ) {
147 applySnapshot(((ApplySnapshot) message).getSnapshot());
149 } else if (message instanceof FindLeader) {
152 context.getPeerAddress(currentBehavior.getLeaderId())),
156 } else if (message instanceof SaveSnapshotSuccess) {
157 SaveSnapshotSuccess success = (SaveSnapshotSuccess) message;
159 // TODO: Not sure if we want to be this aggressive with trimming stuff
160 trimPersistentData(success.metadata().sequenceNr());
162 } else if (message instanceof SaveSnapshotFailure) {
164 // TODO: Handle failure in saving the snapshot
166 } else if (message instanceof FindLeader){
168 getSender().tell(new FindLeaderReply(
169 context.getPeerAddress(currentBehavior.getLeaderId())),
172 } else if (message instanceof AddRaftPeer){
174 // FIXME : Do not add raft peers like this.
175 // When adding a new Peer we have to ensure that the a majority of
176 // the peers know about the new Peer. Doing it this way may cause
177 // a situation where multiple Leaders may emerge
178 AddRaftPeer arp = (AddRaftPeer)message;
179 context.addToPeers(arp.getName(), arp.getAddress());
181 } else if (message instanceof RemoveRaftPeer){
183 RemoveRaftPeer rrp = (RemoveRaftPeer)message;
184 context.removePeer(rrp.getName());
189 currentBehavior.handleMessage(getSender(), message);
190 currentBehavior = switchBehavior(state);
197 * When a derived RaftActor needs to persist something it must call
204 protected void persistData(ActorRef clientActor, String identifier,
207 ReplicatedLogEntry replicatedLogEntry = new ReplicatedLogImplEntry(
208 context.getReplicatedLog().lastIndex() + 1,
209 context.getTermInformation().getCurrentTerm(), data);
211 LOG.debug("Persist data {}", replicatedLogEntry);
214 .appendAndPersist(clientActor, identifier, replicatedLogEntry);
217 protected String getId() {
218 return context.getId();
222 * Derived actors can call the isLeader method to check if the current
223 * RaftActor is the Leader or not
225 * @return true it this RaftActor is a Leader false otherwise
227 protected boolean isLeader() {
228 return context.getId().equals(currentBehavior.getLeaderId());
232 * Derived actor can call getLeader if they need a reference to the Leader.
233 * This would be useful for example in forwarding a request to an actor
234 * which is the leader
236 * @return A reference to the leader if known, null otherwise
238 protected ActorSelection getLeader(){
239 String leaderId = currentBehavior.getLeaderId();
240 if (leaderId == null) {
243 String peerAddress = context.getPeerAddress(leaderId);
244 LOG.debug("getLeader leaderId = " + leaderId + " peerAddress = "
246 return context.actorSelection(peerAddress);
249 protected RaftState getRaftState() {
250 return currentBehavior.state();
254 * setPeerAddress sets the address of a known peer at a later time.
256 * This is to account for situations where a we know that a peer
257 * exists but we do not know an address up-front. This may also be used in
258 * situations where a known peer starts off in a different location and we
259 * need to change it's address
261 * Note that if the peerId does not match the list of peers passed to
262 * this actor during construction an IllegalStateException will be thrown.
267 protected void setPeerAddress(String peerId, String peerAddress){
268 context.setPeerAddress(peerId, peerAddress);
274 * The applyState method will be called by the RaftActor when some data
275 * needs to be applied to the actor's state
277 * @param clientActor A reference to the client who sent this message. This
278 * is the same reference that was passed to persistData
279 * by the derived actor. clientActor may be null when
280 * the RaftActor is behaving as a follower or during
282 * @param identifier The identifier of the persisted data. This is also
283 * the same identifier that was passed to persistData by
284 * the derived actor. identifier may be null when
285 * the RaftActor is behaving as a follower or during
287 * @param data A piece of data that was persisted by the persistData call.
288 * This should NEVER be null.
290 protected abstract void applyState(ActorRef clientActor, String identifier,
294 * This method will be called by the RaftActor when a snapshot needs to be
295 * created. The derived actor should respond with its current state.
297 * During recovery the state that is returned by the derived actor will
298 * be passed back to it by calling the applySnapshot method
300 * @return The current state of the actor
302 protected abstract Object createSnapshot();
305 * This method will be called by the RaftActor during recovery to
306 * reconstruct the state of the actor.
308 * This method may also be called at any other point during normal
309 * operations when the derived actor is out of sync with it's peers
310 * and the only way to bring it in sync is by applying a snapshot
312 * @param snapshot A snapshot of the state of the actor
314 protected abstract void applySnapshot(Object snapshot);
316 private RaftActorBehavior switchBehavior(RaftState state) {
317 if (currentBehavior != null) {
318 if (currentBehavior.state() == state) {
319 return currentBehavior;
321 LOG.info("Switching from state " + currentBehavior.state() + " to "
325 currentBehavior.close();
326 } catch (Exception e) {
328 "Failed to close behavior : " + currentBehavior.state());
332 LOG.info("Switching behavior to " + state);
334 RaftActorBehavior behavior = null;
335 if (state == RaftState.Candidate) {
336 behavior = new Candidate(context);
337 } else if (state == RaftState.Follower) {
338 behavior = new Follower(context);
340 behavior = new Leader(context);
345 private void trimPersistentData(long sequenceNumber) {
347 // FIXME : Not sure how exactly the SnapshotSelectionCriteria is applied
348 // For now guessing that it is ANDed.
349 deleteSnapshots(new SnapshotSelectionCriteria(
350 sequenceNumber - 100000, 43200000));
353 deleteMessages(sequenceNumber);
357 private class ReplicatedLogImpl implements ReplicatedLog {
358 private final List<ReplicatedLogEntry> journal;
359 private final Object snapshot;
360 private long snapshotIndex = -1;
361 private long snapshotTerm = -1;
363 public ReplicatedLogImpl(Snapshot snapshot) {
364 this.snapshot = snapshot.getState();
365 this.snapshotIndex = snapshot.getLastAppliedIndex();
366 this.snapshotTerm = snapshot.getLastAppliedTerm();
368 this.journal = new ArrayList<>(snapshot.getUnAppliedEntries());
371 public ReplicatedLogImpl() {
372 this.snapshot = null;
373 this.journal = new ArrayList<>();
376 @Override public ReplicatedLogEntry get(long index) {
377 int adjustedIndex = adjustedIndex(index);
379 if (adjustedIndex < 0 || adjustedIndex >= journal.size()) {
383 return journal.get(adjustedIndex);
386 @Override public ReplicatedLogEntry last() {
387 if (journal.size() == 0) {
390 return get(journal.size() - 1);
393 @Override public long lastIndex() {
394 if (journal.size() == 0) {
398 return last().getIndex();
401 @Override public long lastTerm() {
402 if (journal.size() == 0) {
406 return last().getTerm();
410 @Override public void removeFrom(long index) {
411 int adjustedIndex = adjustedIndex(index);
413 if (adjustedIndex < 0 || adjustedIndex >= journal.size()) {
417 journal.subList(adjustedIndex , journal.size()).clear();
421 @Override public void removeFromAndPersist(long index) {
422 int adjustedIndex = adjustedIndex(index);
424 if (adjustedIndex < 0 || adjustedIndex >= journal.size()) {
428 // FIXME: Maybe this should be done after the command is saved
429 journal.subList(adjustedIndex , journal.size()).clear();
431 persist(new DeleteEntries(adjustedIndex), new Procedure<DeleteEntries>(){
433 @Override public void apply(DeleteEntries param)
435 //FIXME : Doing nothing for now
442 @Override public void append(
443 final ReplicatedLogEntry replicatedLogEntry) {
444 journal.add(replicatedLogEntry);
447 @Override public List<ReplicatedLogEntry> getFrom(long index) {
448 int adjustedIndex = adjustedIndex(index);
450 List<ReplicatedLogEntry> entries = new ArrayList<>(100);
451 if (adjustedIndex < 0 || adjustedIndex >= journal.size()) {
456 for (int i = adjustedIndex;
457 i < journal.size(); i++) {
458 entries.add(journal.get(i));
463 @Override public void appendAndPersist(
464 final ReplicatedLogEntry replicatedLogEntry) {
465 appendAndPersist(null, null, replicatedLogEntry);
468 public void appendAndPersist(final ActorRef clientActor,
469 final String identifier,
470 final ReplicatedLogEntry replicatedLogEntry) {
471 context.getLogger().debug(
472 "Append log entry and persist {} ", replicatedLogEntry);
473 // FIXME : By adding the replicated log entry to the in-memory journal we are not truly ensuring durability of the logs
474 journal.add(replicatedLogEntry);
476 // When persisting events with persist it is guaranteed that the
477 // persistent actor will not receive further commands between the
478 // persist call and the execution(s) of the associated event
479 // handler. This also holds for multiple persist calls in context
480 // of a single command.
481 persist(replicatedLogEntry,
482 new Procedure<ReplicatedLogEntry>() {
483 public void apply(ReplicatedLogEntry evt) throws Exception {
484 // FIXME : Tentatively create a snapshot every hundred thousand entries. To be tuned.
485 if (size() > 100000) {
486 ReplicatedLogEntry lastAppliedEntry =
487 get(context.getLastApplied());
488 long lastAppliedIndex = -1;
489 long lastAppliedTerm = -1;
490 if (lastAppliedEntry != null) {
491 lastAppliedIndex = lastAppliedEntry.getIndex();
492 lastAppliedTerm = lastAppliedEntry.getTerm();
495 saveSnapshot(Snapshot.create(createSnapshot(),
496 getFrom(context.getLastApplied() + 1),
497 lastIndex(), lastTerm(), lastAppliedIndex,
500 // Send message for replication
501 if (clientActor != null) {
502 currentBehavior.handleMessage(getSelf(),
503 new Replicate(clientActor, identifier,
512 @Override public long size() {
513 return journal.size() + snapshotIndex + 1;
516 @Override public boolean isPresent(long index) {
517 int adjustedIndex = adjustedIndex(index);
519 if (adjustedIndex < 0 || adjustedIndex >= journal.size()) {
525 @Override public boolean isInSnapshot(long index) {
526 return index <= snapshotIndex;
529 @Override public Object getSnapshot() {
533 @Override public long getSnapshotIndex() {
534 return snapshotIndex;
537 @Override public long getSnapshotTerm() {
541 private int adjustedIndex(long index) {
542 if(snapshotIndex < 0){
545 return (int) (index - snapshotIndex);
552 private static class DeleteEntries implements Serializable {
553 private final int fromIndex;
556 public DeleteEntries(int fromIndex) {
557 this.fromIndex = fromIndex;
560 public int getFromIndex() {
566 private static class Snapshot implements Serializable {
567 private final Object state;
568 private final List<ReplicatedLogEntry> unAppliedEntries;
569 private final long lastIndex;
570 private final long lastTerm;
571 private final long lastAppliedIndex;
572 private final long lastAppliedTerm;
574 private Snapshot(Object state,
575 List<ReplicatedLogEntry> unAppliedEntries, long lastIndex,
576 long lastTerm, long lastAppliedIndex, long lastAppliedTerm) {
578 this.unAppliedEntries = unAppliedEntries;
579 this.lastIndex = lastIndex;
580 this.lastTerm = lastTerm;
581 this.lastAppliedIndex = lastAppliedIndex;
582 this.lastAppliedTerm = lastAppliedTerm;
586 public static Snapshot create(Object state,
587 List<ReplicatedLogEntry> entries, long lastIndex, long lastTerm,
588 long lastAppliedIndex, long lastAppliedTerm) {
589 return new Snapshot(state, entries, lastIndex, lastTerm,
590 lastAppliedIndex, lastAppliedTerm);
593 public Object getState() {
597 public List<ReplicatedLogEntry> getUnAppliedEntries() {
598 return unAppliedEntries;
601 public long getLastTerm() {
605 public long getLastAppliedIndex() {
606 return lastAppliedIndex;
609 public long getLastAppliedTerm() {
610 return lastAppliedTerm;
614 private class ElectionTermImpl implements ElectionTerm {
616 * Identifier of the actor whose election term information this is
618 private long currentTerm = 0;
619 private String votedFor = null;
621 public long getCurrentTerm() {
625 public String getVotedFor() {
629 @Override public void update(long currentTerm, String votedFor) {
630 LOG.info("Set currentTerm={}, votedFor={}", currentTerm, votedFor);
632 this.currentTerm = currentTerm;
633 this.votedFor = votedFor;
637 public void updateAndPersist(long currentTerm, String votedFor){
638 update(currentTerm, votedFor);
639 // FIXME : Maybe first persist then update the state
640 persist(new UpdateElectionTerm(this.currentTerm, this.votedFor), new Procedure<UpdateElectionTerm>(){
642 @Override public void apply(UpdateElectionTerm param)
650 private static class UpdateElectionTerm implements Serializable {
651 private final long currentTerm;
652 private final String votedFor;
654 public UpdateElectionTerm(long currentTerm, String votedFor) {
655 this.currentTerm = currentTerm;
656 this.votedFor = votedFor;
659 public long getCurrentTerm() {
663 public String getVotedFor() {