+ private boolean isOutOfSync(AppendEntries appendEntries) {
+
+ long prevLogTerm = getLogEntryTerm(appendEntries.getPrevLogIndex());
+ boolean prevEntryPresent = isLogEntryPresent(appendEntries.getPrevLogIndex());
+ long lastIndex = lastIndex();
+ int numLogEntries = appendEntries.getEntries() != null ? appendEntries.getEntries().size() : 0;
+ boolean outOfSync = true;
+
+ 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 if(appendEntries.getPrevLogIndex() == -1 && appendEntries.getPrevLogTerm() == -1
+ && appendEntries.getReplicatedToAllIndex() != -1
+ && !isLogEntryPresent(appendEntries.getReplicatedToAllIndex())) {
+ // This append entry comes from a leader who has it's log aggressively trimmed and so does not have
+ // the previous entry in it's in-memory journal
+
+ LOG.debug(
+ "{}: Cannot append entries because the replicatedToAllIndex {} does not appear to be in the in-memory journal",
+ logName(), appendEntries.getReplicatedToAllIndex());
+ } else if(appendEntries.getPrevLogIndex() == -1 && appendEntries.getPrevLogTerm() == -1
+ && appendEntries.getReplicatedToAllIndex() != -1 && numLogEntries > 0 &&
+ !isLogEntryPresent(appendEntries.getEntries().get(0).getIndex() - 1)){
+ LOG.debug(
+ "{}: Cannot append entries because the calculated previousIndex {} was not found in the in-memory journal",
+ logName(), appendEntries.getEntries().get(0).getIndex() - 1);
+ } else {
+ outOfSync = false;
+ }
+ return outOfSync;
+ }
+