raft: Remove redundant raft.Commit field.

Keeping this field in sync with `raft.raftLog.committed` was
error-prone, so instead we synthesize the `HardState` on demand.

Fixes #4278.

raft/node.go

@@ -160,7 +160,6 @@ func StartNode(c *Config, peers []Peer) Node {
 	// TODO(bdarnell): These entries are still unstable; do we need to preserve
 	// the invariant that committed < unstable?
 	r.raftLog.committed = r.raftLog.lastIndex()
-	r.Commit = r.raftLog.committed
 	// Now apply them, mainly so that the application can call Campaign
 	// immediately after StartNode in tests. Note that these nodes will
 	// be added to raft twice: here and when the application's Ready
@@ -453,8 +452,8 @@ func newReady(r *raft, prevSoftSt *SoftState, prevHardSt pb.HardState) Ready {
 	if softSt := r.softState(); !softSt.equal(prevSoftSt) {
 		rd.SoftState = softSt
 	}
-	if !isHardStateEqual(r.HardState, prevHardSt) {
-		rd.HardState = r.HardState
+	if hardSt := r.hardState(); !isHardStateEqual(hardSt, prevHardSt) {
+		rd.HardState = hardSt
 	}
 	if r.raftLog.unstable.snapshot != nil {
 		rd.Snapshot = *r.raftLog.unstable.snapshot

raft/raft.go

@@ -138,10 +138,11 @@ func (c *Config) validate() error {
 }
 
 type raft struct {
-	pb.HardState
-
 	id uint64
 
+	Term uint64
+	Vote uint64
+
 	// the log
 	raftLog *raftLog
 
@@ -239,6 +240,14 @@ func (r *raft) hasLeader() bool { return r.lead != None }
 
 func (r *raft) softState() *SoftState { return &SoftState{Lead: r.lead, RaftState: r.state} }
 
+func (r *raft) hardState() pb.HardState {
+	return pb.HardState{
+		Term:   r.Term,
+		Vote:   r.Vote,
+		Commit: r.raftLog.committed,
+	}
+}
+
 func (r *raft) quorum() int { return len(r.prs)/2 + 1 }
 
 func (r *raft) nodes() []uint64 {
@@ -295,7 +304,7 @@ func (r *raft) sendAppend(to uint64) {
 		m.Snapshot = snapshot
 		sindex, sterm := snapshot.Metadata.Index, snapshot.Metadata.Term
 		r.logger.Debugf("%x [firstindex: %d, commit: %d] sent snapshot[index: %d, term: %d] to %x [%s]",
-			r.id, r.raftLog.firstIndex(), r.Commit, sindex, sterm, to, pr)
+			r.id, r.raftLog.firstIndex(), r.raftLog.committed, sindex, sterm, to, pr)
 		pr.becomeSnapshot(sindex)
 		r.logger.Debugf("%x paused sending replication messages to %x [%s]", r.id, to, pr)
 	} else {
@@ -525,7 +534,6 @@ func (r *raft) Step(m pb.Message) error {
 		if r.state != StateLeader {
 			r.logger.Infof("%x is starting a new election at term %d", r.id, r.Term)
 			r.campaign()
-			r.Commit = r.raftLog.committed
 		} else {
 			r.logger.Debugf("%x ignoring MsgHup because already leader", r.id)
 		}
@@ -550,7 +558,6 @@ func (r *raft) Step(m pb.Message) error {
 		return nil
 	}
 	r.step(r, m)
-	r.Commit = r.raftLog.committed
 	return nil
 }
 
@@ -742,8 +749,8 @@ func stepFollower(r *raft, m pb.Message) {
 }
 
 func (r *raft) handleAppendEntries(m pb.Message) {
-	if m.Index < r.Commit {
-		r.send(pb.Message{To: m.From, Type: pb.MsgAppResp, Index: r.Commit})
+	if m.Index < r.raftLog.committed {
+		r.send(pb.Message{To: m.From, Type: pb.MsgAppResp, Index: r.raftLog.committed})
 		return
 	}
 
@@ -765,11 +772,11 @@ func (r *raft) handleSnapshot(m pb.Message) {
 	sindex, sterm := m.Snapshot.Metadata.Index, m.Snapshot.Metadata.Term
 	if r.restore(m.Snapshot) {
 		r.logger.Infof("%x [commit: %d] restored snapshot [index: %d, term: %d]",
-			r.id, r.Commit, sindex, sterm)
+			r.id, r.raftLog.committed, sindex, sterm)
 		r.send(pb.Message{To: m.From, Type: pb.MsgAppResp, Index: r.raftLog.lastIndex()})
 	} else {
 		r.logger.Infof("%x [commit: %d] ignored snapshot [index: %d, term: %d]",
-			r.id, r.Commit, sindex, sterm)
+			r.id, r.raftLog.committed, sindex, sterm)
 		r.send(pb.Message{To: m.From, Type: pb.MsgAppResp, Index: r.raftLog.committed})
 	}
 }
@@ -782,13 +789,13 @@ func (r *raft) restore(s pb.Snapshot) bool {
 	}
 	if r.raftLog.matchTerm(s.Metadata.Index, s.Metadata.Term) {
 		r.logger.Infof("%x [commit: %d, lastindex: %d, lastterm: %d] fast-forwarded commit to snapshot [index: %d, term: %d]",
-			r.id, r.Commit, r.raftLog.lastIndex(), r.raftLog.lastTerm(), s.Metadata.Index, s.Metadata.Term)
+			r.id, r.raftLog.committed, r.raftLog.lastIndex(), r.raftLog.lastTerm(), s.Metadata.Index, s.Metadata.Term)
 		r.raftLog.commitTo(s.Metadata.Index)
 		return false
 	}
 
 	r.logger.Infof("%x [commit: %d, lastindex: %d, lastterm: %d] starts to restore snapshot [index: %d, term: %d]",
-		r.id, r.Commit, r.raftLog.lastIndex(), r.raftLog.lastTerm(), s.Metadata.Index, s.Metadata.Term)
+		r.id, r.raftLog.committed, r.raftLog.lastIndex(), r.raftLog.lastTerm(), s.Metadata.Index, s.Metadata.Term)
 
 	r.raftLog.restore(s)
 	r.prs = make(map[uint64]*Progress)
@@ -848,7 +855,6 @@ func (r *raft) loadState(state pb.HardState) {
 	r.raftLog.committed = state.Commit
 	r.Term = state.Term
 	r.Vote = state.Vote
-	r.Commit = state.Commit
 }
 
 // isElectionTimeout returns true if r.elapsed is greater than the

raft/raft_test.go

@@ -957,8 +957,8 @@ func TestMsgAppRespWaitReset(t *testing.T) {
 		Type:  pb.MsgAppResp,
 		Index: 1,
 	})
-	if sm.Commit != 1 {
-		t.Fatalf("expected Commit to be 1, got %d", sm.Commit)
+	if sm.raftLog.committed != 1 {
+		t.Fatalf("expected committed to be 1, got %d", sm.raftLog.committed)
 	}
 	// Also consume the MsgApp messages that update Commit on the followers.
 	sm.readMessages()
@@ -1046,7 +1046,7 @@ func TestRecvMsgVote(t *testing.T) {
 		case StateLeader:
 			sm.step = stepLeader
 		}
-		sm.HardState = pb.HardState{Vote: tt.voteFor}
+		sm.Vote = tt.voteFor
 		sm.raftLog = &raftLog{
 			storage:  &MemoryStorage{ents: []pb.Entry{{}, {Index: 1, Term: 2}, {Index: 2, Term: 2}}},
 			unstable: unstable{offset: 3},

raft/rawnode.go

@@ -105,7 +105,7 @@ func NewRawNode(config *Config, peers []Peer) (*RawNode, error) {
 	}
 	// Set the initial hard and soft states after performing all initialization.
 	rn.prevSoftSt = r.softState()
-	rn.prevHardSt = r.HardState
+	rn.prevHardSt = r.hardState()
 
 	return rn, nil
 }
@@ -191,7 +191,7 @@ func (rn *RawNode) HasReady() bool {
 	if !r.softState().equal(rn.prevSoftSt) {
 		return true
 	}
-	if !IsEmptyHardState(r.HardState) && !isHardStateEqual(r.HardState, rn.prevHardSt) {
+	if hardSt := r.hardState(); !IsEmptyHardState(hardSt) && !isHardStateEqual(hardSt, rn.prevHardSt) {
 		return true
 	}
 	if r.raftLog.unstable.snapshot != nil && !IsEmptySnap(*r.raftLog.unstable.snapshot) {

raft/status.go

@@ -33,7 +33,7 @@ type Status struct {
 // getStatus gets a copy of the current raft status.
 func getStatus(r *raft) Status {
 	s := Status{ID: r.id}
-	s.HardState = r.HardState
+	s.HardState = r.hardState()
 	s.SoftState = *r.softState()
 
 	s.Applied = r.raftLog.applied