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raft: reset votes when becomePreCandidate #8346

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Aug 3, 2017
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raft: reset votes when becomePreCandidate #8346

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3740793
raft: reset votes when becomePreCandidate
lishuai87 Aug 1, 2017
42cc64a
raft: add TestPreVoteWithSplitVote
lishuai87 Aug 2, 2017
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1 change: 1 addition & 0 deletions raft/raft.go
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Original file line number Diff line number Diff line change
Expand Up @@ -611,6 +611,7 @@ func (r *raft) becomePreCandidate() {
// but doesn't change anything else. In particular it does not increase
// r.Term or change r.Vote.
r.step = stepCandidate
r.votes = make(map[uint64]bool)
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check line612? it says vote should not be changed for some reason. i do not feel it is safe to change the vote decision for one term either.

/cc @bdarnell

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probably if pre-candidate times out, it needs to increase term to handle the potential vote spilt.

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vote is what we voted for, it's in hard state. while votes is what other nodes grant/reject us, it's a memory state.
we can't change vote, but can change votes when a pre-vote happen.

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Right. I misread.

r.tick = r.tickElection
r.state = StatePreCandidate
r.logger.Infof("%x became pre-candidate at term %d", r.id, r.Term)
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77 changes: 77 additions & 0 deletions raft/raft_test.go
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Expand Up @@ -3209,6 +3209,83 @@ func TestNodeWithSmallerTermCanCompleteElection(t *testing.T) {
}
}

// TestPreVoteWithSplitVote verifies that after split vote, cluster can complete
// election in next round.
func TestPreVoteWithSplitVote(t *testing.T) {
n1 := newTestRaft(1, []uint64{1, 2, 3}, 10, 1, NewMemoryStorage())
n2 := newTestRaft(2, []uint64{1, 2, 3}, 10, 1, NewMemoryStorage())
n3 := newTestRaft(3, []uint64{1, 2, 3}, 10, 1, NewMemoryStorage())

n1.becomeFollower(1, None)
n2.becomeFollower(1, None)
n3.becomeFollower(1, None)

n1.preVote = true
n2.preVote = true
n3.preVote = true

nt := newNetwork(n1, n2, n3)
nt.send(pb.Message{From: 1, To: 1, Type: pb.MsgHup})

// simulate leader down. followers start split vote.
nt.isolate(1)
nt.send([]pb.Message{
{From: 2, To: 2, Type: pb.MsgHup},
{From: 3, To: 3, Type: pb.MsgHup},
}...)

// check whether the term values are expected
// n2.Term == 3
// n3.Term == 3
sm := nt.peers[2].(*raft)
if sm.Term != 3 {
t.Errorf("peer 2 term: %d, want %d", sm.Term, 3)
}
sm = nt.peers[3].(*raft)
if sm.Term != 3 {
t.Errorf("peer 3 term: %d, want %d", sm.Term, 3)
}

// check state
// n2 == candidate
// n3 == candidate
sm = nt.peers[2].(*raft)
if sm.state != StateCandidate {
t.Errorf("peer 2 state: %s, want %s", sm.state, StateCandidate)
}
sm = nt.peers[3].(*raft)
if sm.state != StateCandidate {
t.Errorf("peer 3 state: %s, want %s", sm.state, StateCandidate)
}

// node 2 election timeout first
nt.send(pb.Message{From: 2, To: 2, Type: pb.MsgHup})

// check whether the term values are expected
// n2.Term == 4
// n3.Term == 4
sm = nt.peers[2].(*raft)
if sm.Term != 4 {
t.Errorf("peer 2 term: %d, want %d", sm.Term, 4)
}
sm = nt.peers[3].(*raft)
if sm.Term != 4 {
t.Errorf("peer 3 term: %d, want %d", sm.Term, 4)
}

// check state
// n2 == leader
// n3 == follower
sm = nt.peers[2].(*raft)
if sm.state != StateLeader {
t.Errorf("peer 2 state: %s, want %s", sm.state, StateLeader)
}
sm = nt.peers[3].(*raft)
if sm.state != StateFollower {
t.Errorf("peer 3 state: %s, want %s", sm.state, StateFollower)
}
}

func entsWithConfig(configFunc func(*Config), terms ...uint64) *raft {
storage := NewMemoryStorage()
for i, term := range terms {
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