Persists Term in the (bbolt) Backend

CHANGELOG-3.5.md

@@ -76,7 +76,8 @@ See [code changes](https://github.com/etcd-io/etcd/compare/v3.4.0...v3.5.0) and
 ### Storage format changes
 - [WAL log's snapshots persists raftpb.ConfState](https://github.com/etcd-io/etcd/pull/12735)
 - [Backend persists raftpb.ConfState](https://github.com/etcd-io/etcd/pull/12962) in the `meta` bucket `confState` key.
-- Backend persists downgrade in the `cluster` bucket
+- [Backend persists applied term](https://github.com/etcd-io/etcd/pull/) in the `meta` bucket.
+- Backend persists `downgrade` in the `cluster` bucket
 
 ### Security
 

etcdctl/ctlv2/command/backup_command.go

@@ -124,7 +124,7 @@ func handleBackup(c *cli.Context) error {
 
 	walsnap := saveSnap(lg, destSnap, srcSnap, &desired)
 	metadata, state, ents := translateWAL(lg, srcWAL, walsnap, withV3)
-	saveDB(lg, destDbPath, srcDbPath, state.Commit, &desired, withV3)
+	saveDB(lg, destDbPath, srcDbPath, state.Commit, state.Term, &desired, withV3)
 
 	neww, err := wal.Create(lg, destWAL, pbutil.MustMarshal(&metadata))
 	if err != nil {
@@ -265,7 +265,7 @@ func raftEntryToNoOp(entry *raftpb.Entry) {
 }
 
 // saveDB copies the v3 backend and strips cluster information.
-func saveDB(lg *zap.Logger, destDB, srcDB string, idx uint64, desired *desiredCluster, v3 bool) {
+func saveDB(lg *zap.Logger, destDB, srcDB string, idx uint64, term uint64, desired *desiredCluster, v3 bool) {
 
 	// open src db to safely copy db state
 	if v3 {
@@ -322,7 +322,7 @@ func saveDB(lg *zap.Logger, destDB, srcDB string, idx uint64, desired *desiredCl
 		tx.Lock()
 		defer tx.Unlock()
 		cindex.UnsafeCreateMetaBucket(tx)
-		cindex.UnsafeUpdateConsistentIndex(tx, idx, false)
+		cindex.UnsafeUpdateConsistentIndex(tx, idx, term, false)
 	} else {
 		// Thanks to translateWAL not moving entries, but just replacing them with
 		// 'empty', there is no need to update the consistency index.

etcdctl/ctlv3/command/migrate_command.go

@@ -82,7 +82,7 @@ func migrateCommandFunc(cmd *cobra.Command, args []string) {
 		writer, reader, errc = defaultTransformer()
 	}
 
-	st, index := rebuildStoreV2()
+	st, index, term := rebuildStoreV2()
 	be := prepareBackend()
 	defer be.Close()
 
@@ -92,7 +92,7 @@ func migrateCommandFunc(cmd *cobra.Command, args []string) {
 	}()
 
 	readKeys(reader, be)
-	cindex.UpdateConsistentIndex(be.BatchTx(), index, true)
+	cindex.UpdateConsistentIndex(be.BatchTx(), index, term, true)
 	err := <-errc
 	if err != nil {
 		fmt.Println("failed to transform keys")
@@ -127,8 +127,7 @@ func prepareBackend() backend.Backend {
 	return be
 }
 
-func rebuildStoreV2() (v2store.Store, uint64) {
-	var index uint64
+func rebuildStoreV2() (st v2store.Store, index uint64, term uint64) {
 	cl := membership.NewCluster(zap.NewExample())
 
 	waldir := migrateWALdir
@@ -147,6 +146,7 @@ func rebuildStoreV2() (v2store.Store, uint64) {
 	if snapshot != nil {
 		walsnap.Index, walsnap.Term = snapshot.Metadata.Index, snapshot.Metadata.Term
 		index = snapshot.Metadata.Index
+		term = snapshot.Metadata.Term
 	}
 
 	w, err := wal.OpenForRead(zap.NewExample(), waldir, walsnap)
@@ -160,7 +160,7 @@ func rebuildStoreV2() (v2store.Store, uint64) {
 		ExitWithError(ExitError, err)
 	}
 
-	st := v2store.New()
+	st = v2store.New()
 	if snapshot != nil {
 		err := st.Recovery(snapshot.Data)
 		if err != nil {
@@ -191,12 +191,13 @@ func rebuildStoreV2() (v2store.Store, uint64) {
 				applyRequest(req, applier)
 			}
 		}
-		if ent.Index > index {
+		if ent.Index >= index {
 			index = ent.Index
+			term = ent.Term
 		}
 	}
 
-	return st, index
+	return st, index, term
 }
 
 func applyConf(cc raftpb.ConfChange, cl *membership.RaftCluster) {

etcdctl/snapshot/v3_snapshot.go

@@ -265,7 +265,7 @@ func (s *v3Manager) Restore(cfg RestoreConfig) error {
 		return err
 	}
 
-	if err := s.updateCIndex(hardstate.Commit); err != nil {
+	if err := s.updateCIndex(hardstate.Commit, hardstate.Term); err != nil {
 		return err
 	}
 
@@ -475,10 +475,10 @@ func (s *v3Manager) saveWALAndSnap() (*raftpb.HardState, error) {
 	return &hardState, w.SaveSnapshot(snapshot)
 }
 
-func (s *v3Manager) updateCIndex(commit uint64) error {
+func (s *v3Manager) updateCIndex(commit uint64, term uint64) error {
 	be := backend.NewDefaultBackend(s.outDbPath())
 	defer be.Close()
 
-	cindex.UpdateConsistentIndex(be.BatchTx(), commit, false)
+	cindex.UpdateConsistentIndex(be.BatchTx(), commit, term, false)
 	return nil
 }

server/etcdserver/backend.go

@@ -99,7 +99,7 @@ func openBackend(cfg config.ServerConfig, hooks backend.Hooks) backend.Backend {
 func recoverSnapshotBackend(cfg config.ServerConfig, oldbe backend.Backend, snapshot raftpb.Snapshot, beExist bool, hooks backend.Hooks) (backend.Backend, error) {
 	consistentIndex := uint64(0)
 	if beExist {
-		consistentIndex = cindex.ReadConsistentIndex(oldbe.BatchTx())
+		consistentIndex, _ = cindex.ReadConsistentIndex(oldbe.BatchTx())
 	}
 	if snapshot.Metadata.Index <= consistentIndex {
 		return oldbe, nil

server/etcdserver/cindex/cindex.go

@@ -26,6 +26,7 @@ var (
 	MetaBucketName = []byte("meta")
 
 	ConsistentIndexKeyName = []byte("consistent_index")
+	TermKeyName            = []byte("term")
 )
 
 type Backend interface {
@@ -39,7 +40,7 @@ type ConsistentIndexer interface {
 	ConsistentIndex() uint64
 
 	// SetConsistentIndex set the consistent index of current executing entry.
-	SetConsistentIndex(v uint64)
+	SetConsistentIndex(v uint64, term uint64)
 
 	// UnsafeSave must be called holding the lock on the tx.
 	// It saves consistentIndex to the underlying stable storage.
@@ -52,9 +53,13 @@ type ConsistentIndexer interface {
 // consistentIndex implements the ConsistentIndexer interface.
 type consistentIndex struct {
 	// consistentIndex represents the offset of an entry in a consistent replica log.
-	// it caches the "consistent_index" key's value.
+	// It caches the "consistent_index" key's value.
 	// Accessed through atomics so must be 64-bit aligned.
 	consistentIndex uint64
+	// term represents the RAFT term of committed entry in a consistent replica log.
+	// Accessed through atomics so must be 64-bit aligned.
+	// The value is being persisted in the backend since v3.5.
+	term uint64
 
 	// be is used for initial read consistentIndex
 	be Backend
@@ -75,38 +80,44 @@ func (ci *consistentIndex) ConsistentIndex() uint64 {
 	ci.mutex.Lock()
 	defer ci.mutex.Unlock()
 
-	v := ReadConsistentIndex(ci.be.BatchTx())
-	atomic.StoreUint64(&ci.consistentIndex, v)
+	v, term := ReadConsistentIndex(ci.be.BatchTx())
+	ci.SetConsistentIndex(v, term)
 	return v
 }
 
-func (ci *consistentIndex) SetConsistentIndex(v uint64) {
+func (ci *consistentIndex) SetConsistentIndex(v uint64, term uint64) {
 	atomic.StoreUint64(&ci.consistentIndex, v)
+	atomic.StoreUint64(&ci.term, term)
 }
 
 func (ci *consistentIndex) UnsafeSave(tx backend.BatchTx) {
 	index := atomic.LoadUint64(&ci.consistentIndex)
-	UnsafeUpdateConsistentIndex(tx, index, true)
+	term := atomic.LoadUint64(&ci.term)
+	UnsafeUpdateConsistentIndex(tx, index, term, true)
 }
 
 func (ci *consistentIndex) SetBackend(be Backend) {
 	ci.mutex.Lock()
 	defer ci.mutex.Unlock()
 	ci.be = be
 	// After the backend is changed, the first access should re-read it.
-	ci.SetConsistentIndex(0)
+	ci.SetConsistentIndex(0, 0)
 }
 
 func NewFakeConsistentIndex(index uint64) ConsistentIndexer {
 	return &fakeConsistentIndex{index: index}
 }
 
-type fakeConsistentIndex struct{ index uint64 }
+type fakeConsistentIndex struct {
+	index uint64
+	term  uint64
+}
 
 func (f *fakeConsistentIndex) ConsistentIndex() uint64 { return f.index }
 
-func (f *fakeConsistentIndex) SetConsistentIndex(index uint64) {
+func (f *fakeConsistentIndex) SetConsistentIndex(index uint64, term uint64) {
 	atomic.StoreUint64(&f.index, index)
+	atomic.StoreUint64(&f.term, term)
 }
 
 func (f *fakeConsistentIndex) UnsafeSave(_ backend.BatchTx) {}
@@ -124,47 +135,61 @@ func CreateMetaBucket(tx backend.BatchTx) {
 	tx.UnsafeCreateBucket(MetaBucketName)
 }
 
-// unsafeGetConsistentIndex loads consistent index from given transaction.
-// returns 0 if the data are not found.
-func unsafeReadConsistentIndex(tx backend.ReadTx) uint64 {
+// unsafeGetConsistentIndex loads consistent index & term from given transaction.
+// returns 0,0 if the data are not found.
+// Term is persisted since v3.5.
+func unsafeReadConsistentIndex(tx backend.ReadTx) (uint64, uint64) {
 	_, vs := tx.UnsafeRange(MetaBucketName, ConsistentIndexKeyName, nil, 0)
 	if len(vs) == 0 {
-		return 0
+		return 0, 0
 	}
 	v := binary.BigEndian.Uint64(vs[0])
-	return v
+	_, ts := tx.UnsafeRange(MetaBucketName, TermKeyName, nil, 0)
+	if len(ts) == 0 {
+		return v, 0
+	}
+	t := binary.BigEndian.Uint64(ts[0])
+	return v, t
 }
 
-// ReadConsistentIndex loads consistent index from given transaction.
+// ReadConsistentIndex loads consistent index and term from given transaction.
 // returns 0 if the data are not found.
-func ReadConsistentIndex(tx backend.ReadTx) uint64 {
+func ReadConsistentIndex(tx backend.ReadTx) (uint64, uint64) {
 	tx.Lock()
 	defer tx.Unlock()
 	return unsafeReadConsistentIndex(tx)
 }
 
-func UnsafeUpdateConsistentIndex(tx backend.BatchTx, index uint64, onlyGrow bool) {
+func UnsafeUpdateConsistentIndex(tx backend.BatchTx, index uint64, term uint64, onlyGrow bool) {
 	if index == 0 {
 		// Never save 0 as it means that we didn't loaded the real index yet.
 		return
 	}
 
 	if onlyGrow {
-		oldi := unsafeReadConsistentIndex(tx)
-		if index <= oldi {
+		oldi, oldTerm := unsafeReadConsistentIndex(tx)
+		if term < oldTerm {
+			return
+		}
+		if term == oldTerm && index <= oldi {
 			return
 		}
 	}
 
-	bs := make([]byte, 8) // this is kept on stack (not heap) so its quick.
-	binary.BigEndian.PutUint64(bs, index)
+	bs1 := make([]byte, 8)
+	binary.BigEndian.PutUint64(bs1, index)
 	// put the index into the underlying backend
 	// tx has been locked in TxnBegin, so there is no need to lock it again
-	tx.UnsafePut(MetaBucketName, ConsistentIndexKeyName, bs)
+	tx.UnsafePut(MetaBucketName, ConsistentIndexKeyName, bs1)
+	if term > 0 {
+		bs2 := make([]byte, 8)
+		binary.BigEndian.PutUint64(bs2, term)
+		tx.UnsafePut(MetaBucketName, TermKeyName, bs2)
+	}
 }
 
-func UpdateConsistentIndex(tx backend.BatchTx, index uint64, onlyGrow bool) {
+func UpdateConsistentIndex(tx backend.BatchTx, index uint64, term uint64, onlyGrow bool) {
 	tx.Lock()
 	defer tx.Unlock()
-	UnsafeUpdateConsistentIndex(tx, index, onlyGrow)
+	UnsafeUpdateConsistentIndex(tx, index, term, onlyGrow)
 }

server/etcdserver/cindex/cindex_test.go

@@ -19,6 +19,7 @@ import (
 	"testing"
 	"time"
 
+	"github.com/stretchr/testify/assert"
 	"go.etcd.io/etcd/server/v3/mvcc/backend"
 	betesting "go.etcd.io/etcd/server/v3/mvcc/backend/testing"
 )
@@ -38,8 +39,9 @@ func TestConsistentIndex(t *testing.T) {
 	UnsafeCreateMetaBucket(tx)
 	tx.Unlock()
 	be.ForceCommit()
-	r := rand.Uint64()
-	ci.SetConsistentIndex(r)
+	r := uint64(7890123)
+	term := uint64(234)
+	ci.SetConsistentIndex(r, term)
 	index := ci.ConsistentIndex()
 	if index != r {
 		t.Errorf("expected %d,got %d", r, index)
@@ -54,15 +56,11 @@ func TestConsistentIndex(t *testing.T) {
 	defer b.Close()
 	ci.SetBackend(b)
 	index = ci.ConsistentIndex()
-	if index != r {
-		t.Errorf("expected %d,got %d", r, index)
-	}
+	assert.Equal(t, r, index)
 
 	ci = NewConsistentIndex(b)
 	index = ci.ConsistentIndex()
-	if index != r {
-		t.Errorf("expected %d,got %d", r, index)
-	}
+	assert.Equal(t, r, index)
 }
 
 func TestFakeConsistentIndex(t *testing.T) {
@@ -74,7 +72,7 @@ func TestFakeConsistentIndex(t *testing.T) {
 		t.Errorf("expected %d,got %d", r, index)
 	}
 	r = rand.Uint64()
-	ci.SetConsistentIndex(r)
+	ci.SetConsistentIndex(r, 5)
 	index = ci.ConsistentIndex()
 	if index != r {
 		t.Errorf("expected %d,got %d", r, index)

server/etcdserver/server.go

@@ -2124,7 +2124,7 @@ func (s *EtcdServer) apply(
 
 			// set the consistent index of current executing entry
 			if e.Index > s.consistIndex.ConsistentIndex() {
-				s.consistIndex.SetConsistentIndex(e.Index)
+				s.consistIndex.SetConsistentIndex(e.Index, e.Term)
 				shouldApplyV3 = membership.ApplyBoth
 			}
 
@@ -2154,7 +2154,7 @@ func (s *EtcdServer) applyEntryNormal(e *raftpb.Entry) {
 	index := s.consistIndex.ConsistentIndex()
 	if e.Index > index {
 		// set the consistent index of current executing entry
-		s.consistIndex.SetConsistentIndex(e.Index)
+		s.consistIndex.SetConsistentIndex(e.Index, e.Term)
 		shouldApplyV3 = membership.ApplyBoth
 	}
 	s.lg.Debug("apply entry normal",

server/etcdserver/server_test.go

@@ -678,6 +678,7 @@ func TestApplyConfigChangeUpdatesConsistIndex(t *testing.T) {
 	cc := &raftpb.ConfChange{Type: raftpb.ConfChangeAddNode, NodeID: 2, Context: b}
 	ents := []raftpb.Entry{{
 		Index: 2,
+		Term:  4,
 		Type:  raftpb.EntryConfChange,
 		Data:  pbutil.MustMarshal(cc),
 	}}
@@ -695,7 +696,9 @@ func TestApplyConfigChangeUpdatesConsistIndex(t *testing.T) {
 		srv.beHooks.OnPreCommitUnsafe(tx)
 		assert.Equal(t, raftpb.ConfState{Voters: []uint64{2}}, *membership.UnsafeConfStateFromBackend(lg, tx))
 	})
-	assert.Equal(t, consistIndex, cindex.ReadConsistentIndex(be.BatchTx()))
+	rindex, rterm := cindex.ReadConsistentIndex(be.BatchTx())
+	assert.Equal(t, consistIndex, rindex)
+	assert.Equal(t, uint64(4), rterm)
 }
 
 func realisticRaftNode(lg *zap.Logger) *raftNode {

server/mvcc/kvstore.go

@@ -305,6 +305,7 @@ func init() {
 		// consistent index might be changed due to v2 internal sync, which
 		// is not controllable by the user.
 		{Bucket: string(MetaBucketName), Key: string(cindex.ConsistentIndexKeyName)}: {},
+		{Bucket: string(MetaBucketName), Key: string(cindex.TermKeyName)}:            {},
 	}
 }
 

server/mvcc/kvstore_bench_test.go

@@ -79,7 +79,7 @@ func BenchmarkConsistentIndex(b *testing.B) {
 	defer betesting.Close(b, be)
 
 	// This will force the index to be reread from scratch on each call.
-	ci.SetConsistentIndex(0)
+	ci.SetConsistentIndex(0, 0)
 
 	tx := be.BatchTx()
 	tx.Lock()