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raft: fix out-of-order terms #47

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raft: fix out-of-order terms #47

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10 changes: 8 additions & 2 deletions log.go
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Original file line number Diff line number Diff line change
Expand Up @@ -371,11 +371,17 @@ func (l *raftLog) stableSnapTo(i uint64) { l.unstable.stableSnapTo(i) }
func (l *raftLog) acceptUnstable() { l.unstable.acceptInProgress() }

func (l *raftLog) lastTerm() uint64 {
t, err := l.term(l.lastIndex())
_, term := l.tip()
return term
}

func (l *raftLog) tip() (index, term uint64) {
index = l.lastIndex()
t, err := l.term(index)
if err != nil {
l.logger.Panicf("unexpected error when getting the last term (%v)", err)
}
return t
return index, t
}

func (l *raftLog) term(i uint64) (uint64, error) {
Expand Down
15 changes: 14 additions & 1 deletion raft.go
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Original file line number Diff line number Diff line change
Expand Up @@ -757,7 +757,10 @@ func (r *raft) reset(term uint64) {
}

func (r *raft) appendEntry(es ...pb.Entry) (accepted bool) {
li := r.raftLog.lastIndex()
li, lt := r.raftLog.tip()
if r.Term < lt {
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after the first successful appendEntry lt == r.Term, because es[i].Term = r.Term on line 765. So, I don't think this check should be here. It probably should happen at the end of raft.newRaft().

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+1

r.logger.Panicf("%x appending out-of-order term: %d < %d", r.id, r.Term, lt)
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@lavacat lavacat Apr 14, 2023 •
edited
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nit: you aren't checking Terms in es, so msg is a bit confusing. Maybe appending out-of-order term -> last raft log entry has term greater than raft struct

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how about using warning instead of panic?

}
for i := range es {
es[i].Term = r.Term
es[i].Index = li + 1 + uint64(i)
Expand Down Expand Up @@ -1727,6 +1730,16 @@ func (r *raft) restore(s pb.Snapshot) bool {
return false
}

// Another defense-in-depth: the follower is seeing a snapshot at a bigger
// term, but hasn't updated its own term.
if s.Metadata.Term > r.Term {
r.logger.Warningf("%x attempted to restore snapshot at term %d while being at earlier term %d; "+
"should transition to follower at a larger term first",
r.id, s.Metadata.Term, r.Term)
r.becomeFollower(s.Metadata.Term, None)
return false
}

// More defense-in-depth: throw away snapshot if recipient is not in the
// config. This shouldn't ever happen (at the time of writing) but lots of
// code here and there assumes that r.id is in the progress tracker.
Expand Down
22 changes: 12 additions & 10 deletions raft_snap_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -17,6 +17,8 @@ package raft
import (
"testing"

"github.com/stretchr/testify/require"

pb "go.etcd.io/raft/v3/raftpb"
)

Expand All @@ -33,8 +35,8 @@ var (
func TestSendingSnapshotSetPendingSnapshot(t *testing.T) {
storage := newTestMemoryStorage(withPeers(1))
sm := newTestRaft(1, 10, 1, storage)
sm.restore(testingSnap)

sm.becomeFollower(testingSnap.Metadata.Term, 0)
require.True(t, sm.restore(testingSnap))
sm.becomeCandidate()
sm.becomeLeader()

Expand All @@ -51,8 +53,8 @@ func TestSendingSnapshotSetPendingSnapshot(t *testing.T) {
func TestPendingSnapshotPauseReplication(t *testing.T) {
storage := newTestMemoryStorage(withPeers(1, 2))
sm := newTestRaft(1, 10, 1, storage)
sm.restore(testingSnap)

sm.becomeFollower(testingSnap.Metadata.Term, 0)
require.True(t, sm.restore(testingSnap))
sm.becomeCandidate()
sm.becomeLeader()

Expand All @@ -68,8 +70,8 @@ func TestPendingSnapshotPauseReplication(t *testing.T) {
func TestSnapshotFailure(t *testing.T) {
storage := newTestMemoryStorage(withPeers(1, 2))
sm := newTestRaft(1, 10, 1, storage)
sm.restore(testingSnap)

sm.becomeFollower(testingSnap.Metadata.Term, 0)
require.True(t, sm.restore(testingSnap))
sm.becomeCandidate()
sm.becomeLeader()

Expand All @@ -91,8 +93,8 @@ func TestSnapshotFailure(t *testing.T) {
func TestSnapshotSucceed(t *testing.T) {
storage := newTestMemoryStorage(withPeers(1, 2))
sm := newTestRaft(1, 10, 1, storage)
sm.restore(testingSnap)

sm.becomeFollower(testingSnap.Metadata.Term, 0)
require.True(t, sm.restore(testingSnap))
sm.becomeCandidate()
sm.becomeLeader()

Expand All @@ -114,8 +116,8 @@ func TestSnapshotSucceed(t *testing.T) {
func TestSnapshotAbort(t *testing.T) {
storage := newTestMemoryStorage(withPeers(1, 2))
sm := newTestRaft(1, 10, 1, storage)
sm.restore(testingSnap)

sm.becomeFollower(testingSnap.Metadata.Term, 0)
require.True(t, sm.restore(testingSnap))
sm.becomeCandidate()
sm.becomeLeader()

Expand Down
65 changes: 24 additions & 41 deletions raft_test.go
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Expand Up @@ -1366,11 +1366,11 @@ func TestHandleHeartbeat(t *testing.T) {
// TestHandleHeartbeatResp ensures that we re-send log entries when we get a heartbeat response.
func TestHandleHeartbeatResp(t *testing.T) {
storage := newTestMemoryStorage(withPeers(1, 2))
storage.SetHardState(pb.HardState{Term: 3, Vote: 1, Commit: 3})
storage.Append([]pb.Entry{{Index: 1, Term: 1}, {Index: 2, Term: 2}, {Index: 3, Term: 3}})
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are these entries necessary for the test? Maybe both storage.SetHardState and storage.Append can be removed to keep things simpler

sm := newTestRaft(1, 5, 1, storage)
sm.becomeCandidate()
sm.becomeLeader()
sm.raftLog.commitTo(sm.raftLog.lastIndex())

// A heartbeat response from a node that is behind; re-send MsgApp
sm.Step(pb.Message{From: 2, Type: pb.MsgHeartbeatResp})
Expand Down Expand Up @@ -2916,9 +2916,8 @@ func TestRestore(t *testing.T) {

storage := newTestMemoryStorage(withPeers(1, 2))
sm := newTestRaft(1, 10, 1, storage)
if ok := sm.restore(s); !ok {
t.Fatal("restore fail, want succeed")
}
sm.becomeFollower(s.Metadata.Term, 0)
require.True(t, sm.restore(s))

if sm.raftLog.lastIndex() != s.Metadata.Index {
t.Errorf("log.lastIndex = %d, want %d", sm.raftLog.lastIndex(), s.Metadata.Index)
Expand Down Expand Up @@ -2955,9 +2954,8 @@ func TestRestoreWithLearner(t *testing.T) {

storage := newTestMemoryStorage(withPeers(1, 2), withLearners(3))
sm := newTestLearnerRaft(3, 8, 2, storage)
if ok := sm.restore(s); !ok {
t.Error("restore fail, want succeed")
}
sm.becomeFollower(s.Metadata.Term, 0)
require.True(t, sm.restore(s))

if sm.raftLog.lastIndex() != s.Metadata.Index {
t.Errorf("log.lastIndex = %d, want %d", sm.raftLog.lastIndex(), s.Metadata.Index)
Expand Down Expand Up @@ -3001,9 +2999,8 @@ func TestRestoreWithVotersOutgoing(t *testing.T) {

storage := newTestMemoryStorage(withPeers(1, 2))
sm := newTestRaft(1, 10, 1, storage)
if ok := sm.restore(s); !ok {
t.Fatal("restore fail, want succeed")
}
sm.becomeFollower(s.Metadata.Term, 0)
require.True(t, sm.restore(s))

if sm.raftLog.lastIndex() != s.Metadata.Index {
t.Errorf("log.lastIndex = %d, want %d", sm.raftLog.lastIndex(), s.Metadata.Index)
Expand Down Expand Up @@ -3047,13 +3044,9 @@ func TestRestoreVoterToLearner(t *testing.T) {

storage := newTestMemoryStorage(withPeers(1, 2, 3))
sm := newTestRaft(3, 10, 1, storage)

if sm.isLearner {
t.Errorf("%x is learner, want not", sm.id)
}
if ok := sm.restore(s); !ok {
t.Error("restore failed unexpectedly")
}
sm.becomeFollower(s.Metadata.Term, 0)
require.True(t, !sm.isLearner)
require.True(t, sm.restore(s))
}

// TestRestoreLearnerPromotion checks that a learner can become to a follower after
Expand All @@ -3069,18 +3062,10 @@ func TestRestoreLearnerPromotion(t *testing.T) {

storage := newTestMemoryStorage(withPeers(1, 2), withLearners(3))
sm := newTestLearnerRaft(3, 10, 1, storage)

if !sm.isLearner {
t.Errorf("%x is not learner, want yes", sm.id)
}

if ok := sm.restore(s); !ok {
t.Error("restore fail, want succeed")
}

if sm.isLearner {
t.Errorf("%x is learner, want not", sm.id)
}
require.True(t, sm.isLearner)
sm.becomeFollower(s.Metadata.Term, 0)
require.True(t, sm.restore(s))
require.True(t, !sm.isLearner)
}

// TestLearnerReceiveSnapshot tests that a learner can receive a snpahost from leader
Expand All @@ -3096,13 +3081,13 @@ func TestLearnerReceiveSnapshot(t *testing.T) {

store := newTestMemoryStorage(withPeers(1), withLearners(2))
n1 := newTestLearnerRaft(1, 10, 1, store)
n2 := newTestLearnerRaft(2, 10, 1, newTestMemoryStorage(withPeers(1), withLearners(2)))

n1.restore(s)
n1.becomeFollower(s.Metadata.Term, 0)
require.True(t, n1.restore(s))
snap := n1.raftLog.nextUnstableSnapshot()
store.ApplySnapshot(*snap)
n1.appliedSnap(snap)

n2 := newTestLearnerRaft(2, 10, 1, newTestMemoryStorage(withPeers(1), withLearners(2)))
nt := newNetwork(n1, n2)

setRandomizedElectionTimeout(n1, n1.electionTimeout)
Expand Down Expand Up @@ -3132,6 +3117,7 @@ func TestRestoreIgnoreSnapshot(t *testing.T) {
ConfState: pb.ConfState{Voters: []uint64{1, 2}},
},
}
sm.becomeFollower(s.Metadata.Term, 0)

// ignore snapshot
if ok := sm.restore(s); ok {
Expand Down Expand Up @@ -3162,8 +3148,8 @@ func TestProvideSnap(t *testing.T) {
}
storage := newTestMemoryStorage(withPeers(1))
sm := newTestRaft(1, 10, 1, storage)
sm.restore(s)

sm.becomeFollower(s.Metadata.Term, 0)
require.True(t, sm.restore(s))
sm.becomeCandidate()
sm.becomeLeader()

Expand Down Expand Up @@ -3192,8 +3178,8 @@ func TestIgnoreProvidingSnap(t *testing.T) {
}
storage := newTestMemoryStorage(withPeers(1))
sm := newTestRaft(1, 10, 1, storage)
sm.restore(s)

sm.becomeFollower(s.Metadata.Term, 0)
require.True(t, sm.restore(s))
sm.becomeCandidate()
sm.becomeLeader()

Expand All @@ -3218,14 +3204,11 @@ func TestRestoreFromSnapMsg(t *testing.T) {
ConfState: pb.ConfState{Voters: []uint64{1, 2}},
},
}
m := pb.Message{Type: pb.MsgSnap, From: 1, Term: 2, Snapshot: s}
m := pb.Message{Type: pb.MsgSnap, From: 1, Term: 11, Snapshot: s}

sm := newTestRaft(2, 10, 1, newTestMemoryStorage(withPeers(1, 2)))
sm.Step(m)

if sm.lead != uint64(1) {
t.Errorf("sm.lead = %d, want 1", sm.lead)
}
require.Equal(t, uint64(1), sm.lead)

// TODO(bdarnell): what should this test?
}
Expand Down