+ super(context, RaftState.Follower);
+
+ scheduleElection(electionDuration());
+
+ initialSyncStatusTracker = new InitialSyncStatusTracker(context.getActor());
+ }
+
+ private boolean isLogEntryPresent(long index){
+ if(index == context.getReplicatedLog().getSnapshotIndex()){
+ return true;
+ }
+
+ ReplicatedLogEntry previousEntry = context.getReplicatedLog()
+ .get(index);
+
+ return previousEntry != null;
+
+ }
+
+ private long getLogEntryTerm(long index){
+ if(index == context.getReplicatedLog().getSnapshotIndex()){
+ return context.getReplicatedLog().getSnapshotTerm();
+ }
+
+ ReplicatedLogEntry previousEntry = context.getReplicatedLog()
+ .get(index);
+
+ if(previousEntry != null){
+ return previousEntry.getTerm();
+ }
+
+ return -1;
+ }
+
+ private void updateInitialSyncStatus(long currentLeaderCommit, String leaderId){
+ initialSyncStatusTracker.update(leaderId, currentLeaderCommit, context.getCommitIndex());
+ }
+
+ @Override protected RaftActorBehavior handleAppendEntries(ActorRef sender,
+ AppendEntries appendEntries) {
+
+ int numLogEntries = appendEntries.getEntries() != null ? appendEntries.getEntries().size() : 0;
+ if(LOG.isTraceEnabled()) {
+ LOG.trace("{}: handleAppendEntries: {}", logName(), appendEntries);
+ } else if(LOG.isDebugEnabled() && numLogEntries > 0) {
+ LOG.debug("{}: handleAppendEntries: {}", logName(), appendEntries);
+ }
+
+ // TODO : Refactor this method into a bunch of smaller methods
+ // to make it easier to read. Before refactoring ensure tests
+ // cover the code properly
+
+ // 1. Reply false if term < currentTerm (§5.1)
+ // This is handled in the appendEntries method of the base class
+
+ // If we got here then we do appear to be talking to the leader
+ leaderId = appendEntries.getLeaderId();
+
+ // 2. Reply false if log doesn’t contain an entry at prevLogIndex
+ // whose term matches prevLogTerm (§5.3)
+
+ long prevLogTerm = getLogEntryTerm(appendEntries.getPrevLogIndex());
+ boolean prevEntryPresent = isLogEntryPresent(appendEntries.getPrevLogIndex());
+
+ updateInitialSyncStatus(appendEntries.getLeaderCommit(), appendEntries.getLeaderId());
+
+ boolean outOfSync = true;
+
+ // First check if the logs are in sync or not
+ long lastIndex = lastIndex();
+ if (lastIndex == -1 && appendEntries.getPrevLogIndex() != -1) {
+
+ // The follower's log is out of sync because the leader does have
+ // an entry at prevLogIndex and this follower has no entries in
+ // it's log.
+
+ LOG.debug("{}: The followers log is empty and the senders prevLogIndex is {}",
+ logName(), appendEntries.getPrevLogIndex());
+ } else if (lastIndex > -1 && appendEntries.getPrevLogIndex() != -1 && !prevEntryPresent) {
+
+ // The follower's log is out of sync because the Leader's
+ // prevLogIndex entry was not found in it's log
+
+ LOG.debug("{}: The log is not empty but the prevLogIndex {} was not found in it",
+ logName(), appendEntries.getPrevLogIndex());
+ } else if (lastIndex > -1 && prevEntryPresent && prevLogTerm != appendEntries.getPrevLogTerm()) {
+
+ // The follower's log is out of sync because the Leader's
+ // prevLogIndex entry does exist in the follower's log but it has
+ // a different term in it
+
+ LOG.debug(
+ "{}: Cannot append entries because previous entry term {} is not equal to append entries prevLogTerm {}",
+ logName(), prevLogTerm, appendEntries.getPrevLogTerm());
+ } else {
+ outOfSync = false;
+ }
+
+ if (outOfSync) {
+ // We found that the log was out of sync so just send a negative
+ // reply and return
+
+ LOG.debug("{}: Follower is out-of-sync, so sending negative reply, lastIndex: {}, lastTerm: {}",
+ logName(), lastIndex, lastTerm());
+
+ sender.tell(new AppendEntriesReply(context.getId(), currentTerm(), false, lastIndex,
+ lastTerm()), actor());
+ return this;
+ }
+
+ if (appendEntries.getEntries() != null && appendEntries.getEntries().size() > 0) {
+
+ LOG.debug("{}: Number of entries to be appended = {}", logName(),
+ appendEntries.getEntries().size());
+
+ // 3. If an existing entry conflicts with a new one (same index
+ // but different terms), delete the existing entry and all that
+ // follow it (§5.3)
+ int addEntriesFrom = 0;
+ if (context.getReplicatedLog().size() > 0) {
+
+ // Find the entry up until which the one that is not in the follower's log
+ for (int i = 0;i < appendEntries.getEntries().size(); i++, addEntriesFrom++) {
+ ReplicatedLogEntry matchEntry = appendEntries.getEntries().get(i);
+ ReplicatedLogEntry newEntry = context.getReplicatedLog().get(matchEntry.getIndex());
+
+ if (newEntry == null) {
+ //newEntry not found in the log
+ break;
+ }
+
+ if (newEntry.getTerm() == matchEntry.getTerm()) {
+ continue;
+ }
+
+ LOG.debug("{}: Removing entries from log starting at {}", logName(),
+ matchEntry.getIndex());
+
+ // Entries do not match so remove all subsequent entries
+ context.getReplicatedLog().removeFromAndPersist(matchEntry.getIndex());
+ break;
+ }
+ }
+
+ lastIndex = lastIndex();
+ LOG.debug("{}: After cleanup entries to be added from = {}", logName(),
+ (addEntriesFrom + lastIndex));
+
+ // 4. Append any new entries not already in the log
+ for (int i = addEntriesFrom; i < appendEntries.getEntries().size(); i++) {
+ ReplicatedLogEntry entry = appendEntries.getEntries().get(i);
+
+ LOG.debug("{}: Append entry to log {}", logName(), entry.getData());
+
+ context.getReplicatedLog().appendAndPersist(entry);
+ }
+
+ LOG.debug("{}: Log size is now {}", logName(), context.getReplicatedLog().size());
+ }
+
+ // 5. If leaderCommit > commitIndex, set commitIndex =
+ // min(leaderCommit, index of last new entry)
+
+ lastIndex = lastIndex();
+ long prevCommitIndex = context.getCommitIndex();
+
+ context.setCommitIndex(Math.min(appendEntries.getLeaderCommit(), lastIndex));
+
+ if (prevCommitIndex != context.getCommitIndex()) {
+ LOG.debug("{}: Commit index set to {}", logName(), context.getCommitIndex());
+ }
+
+ // If commitIndex > lastApplied: increment lastApplied, apply
+ // log[lastApplied] to state machine (§5.3)
+ // check if there are any entries to be applied. last-applied can be equal to last-index
+ if (appendEntries.getLeaderCommit() > context.getLastApplied() &&
+ context.getLastApplied() < lastIndex) {
+ if(LOG.isDebugEnabled()) {
+ LOG.debug("{}: applyLogToStateMachine, " +
+ "appendEntries.getLeaderCommit(): {}," +
+ "context.getLastApplied(): {}, lastIndex(): {}", logName(),
+ appendEntries.getLeaderCommit(), context.getLastApplied(), lastIndex);
+ }
+
+ applyLogToStateMachine(appendEntries.getLeaderCommit());
+ }
+
+ AppendEntriesReply reply = new AppendEntriesReply(context.getId(), currentTerm(), true,
+ lastIndex, lastTerm());
+
+ if(LOG.isTraceEnabled()) {
+ LOG.trace("{}: handleAppendEntries returning : {}", logName(), reply);
+ } else if(LOG.isDebugEnabled() && numLogEntries > 0) {
+ LOG.debug("{}: handleAppendEntries returning : {}", logName(), reply);
+ }
+
+ sender.tell(reply, actor());
+
+ if (!context.isSnapshotCaptureInitiated()) {
+ super.performSnapshotWithoutCapture(appendEntries.getReplicatedToAllIndex());
+ }
+
+ return this;
+ }
+
+ @Override protected RaftActorBehavior handleAppendEntriesReply(ActorRef sender,
+ AppendEntriesReply appendEntriesReply) {
+ return this;
+ }
+
+ @Override protected RaftActorBehavior handleRequestVoteReply(ActorRef sender,
+ RequestVoteReply requestVoteReply) {
+ return this;