Delay the next campaign if the node lost the vote

Delay the next campaign if the node lost the vote. It's
highly likely it will also lose next campaign, so it makes
more sense to prioritize campaigns by other nodes within
the current term.

Signed-off-by: Benjamin Wang <benjamin.ahrtr@gmail.com>

raft.go

@@ -1674,6 +1674,13 @@ func stepCandidate(r *raft, m pb.Message) error {
 			// pb.MsgPreVoteResp contains future term of pre-candidate
 			// m.Term > r.Term; reuse r.Term
 			r.becomeFollower(r.Term, None)
+			// Delay the next campaign if the node lost the vote. It's
+			// highly likely it will also lose next campaign, so it makes
+			// more sense to prioritize campaigns by other nodes within
+			// the current term.
+			if myVoteRespType == pb.MsgVoteResp {
+				r.randomizedElectionTimeout += r.electionTimeout
+			}
 		}
 	case pb.MsgTimeoutNow:
 		r.logger.Debugf("%x [term %d state %v] ignored MsgTimeoutNow from %x", r.id, r.Term, r.state, m.From)

raft_test.go

@@ -1241,6 +1241,36 @@ func TestPastElectionTimeout(t *testing.T) {
 	}
 }
 
+func TestRandomizedElectionTimeoutOnLostVote(t *testing.T) {
+	storage := newTestMemoryStorage(withPeers(1, 2, 3))
+	storage.Append(index(1).terms(1, 2, 3, 4, 5))
+	r := newTestRaft(1, 10, 1, storage)
+
+	term, index := r.raftLog.lastEntryID().term, r.raftLog.lastEntryID().index
+	r.Term = term
+
+	r.becomeCandidate()
+	msgVote := pb.Message{
+		From:    1,
+		To:      2,
+		Type:    pb.MsgVote,
+		Term:    term + 1,
+		LogTerm: index,
+		Index:   42,
+	}
+	r.stepOrSend([]pb.Message{msgVote})
+
+	// The MsgVote is rejected by r2
+	err := r.Step(pb.Message{From: 2, To: 1, Term: term + 1, Type: pb.MsgVoteResp, Reject: true})
+	require.NoError(t, err)
+	require.Less(t, r.randomizedElectionTimeout, r.electionTimeout*2)
+
+	// The MsgVote is rejected by r3
+	err = r.Step(pb.Message{From: 3, To: 1, Term: term + 1, Type: pb.MsgVoteResp, Reject: true})
+	require.NoError(t, err)
+	require.GreaterOrEqual(t, r.randomizedElectionTimeout, r.electionTimeout*2)
+}
+
 // TestStepIgnoreOldTermMsg to ensure that the Step function ignores the message
 // from old term and does not pass it to the actual stepX function.
 func TestStepIgnoreOldTermMsg(t *testing.T) {