Do not reset the electionElapsed if the node doesn't grant vote or pr…

…eVote

Signed-off-by: Benjamin Wang <[email protected]>

raft.go

@@ -1076,13 +1076,9 @@ func (r *raft) Step(m pb.Message) error {
 				return nil
 			}
 
-			if m.Type == pb.MsgPreVote {
-				// Never change our term in response to a PreVote
-			} else {
-				// m.Type == pb.MsgVote
+			if m.Type == pb.MsgVote {
 				r.logger.Infof("%x [term: %d] received a pb.MsgVote message with higher term from %x [term: %d]",
 					r.id, r.Term, m.From, m.Term)
-				r.becomeFollower(m.Term, None)
 			}
 		} else if m.Type == pb.MsgPreVoteResp && !m.Reject {
 			// We send pre-vote requests with a term in our future. If the
@@ -1190,6 +1186,11 @@ func (r *raft) Step(m pb.Message) error {
 		lastID := r.raftLog.lastEntryID()
 		candLastID := entryID{term: m.LogTerm, index: m.Index}
 		if canVote && r.raftLog.isUpToDate(candLastID) {
+			// The local node should turn into a follower as long as it
+			// grants the vote.
+			if m.Term > r.Term && m.Type == pb.MsgVote {
+				r.becomeFollower(m.Term, None)
+			}
 			// Note: it turns out that that learners must be allowed to cast votes.
 			// This seems counter- intuitive but is necessary in the situation in which
 			// a learner has been promoted (i.e. is now a voter) but has not learned
@@ -1226,6 +1227,21 @@ func (r *raft) Step(m pb.Message) error {
 				r.Vote = m.From
 			}
 		} else {
+			if m.Term > r.Term && m.Type == pb.MsgVote {
+				// If the local node receives a message with higher term,
+				// but it doesn't grant the vote; it turns into a follower,
+				// but it shouldn't reset the electionElapsed, to ensure it
+				// has higher priority to start a campaign in the next round
+				// of election. If we reject a node, it's highly likely we
+				// will reject it again if it immediately campaigns again.
+				// So it may waste a long time to elect a leader if we reset
+				// the electionElapsed.
+				bakElectionElapsed, bakRandomizedElectionTimeout := r.electionElapsed, r.randomizedElectionTimeout
+				r.becomeFollower(m.Term, None)
+				r.electionElapsed = bakElectionElapsed
+				r.randomizedElectionTimeout = bakRandomizedElectionTimeout
+			}
+
 			r.logger.Infof("%x [logterm: %d, index: %d, vote: %x] rejected %s from %x [logterm: %d, index: %d] at term %d",
 				r.id, lastID.term, lastID.index, r.Vote, m.Type, m.From, candLastID.term, candLastID.index, r.Term)
 			r.send(pb.Message{To: m.From, Term: r.Term, Type: voteRespMsgType(m.Type), Reject: true})