func (l Lease) removeFrom(b backend.Backend) {
	key := int64ToBytes(int64(l.ID))

	b.BatchTx().Lock()
	b.BatchTx().UnsafeDelete(leaseBucketName, key)
	b.BatchTx().Unlock()
}

func mustSaveClusterVersionToBackend(be backend.Backend, ver *semver.Version) {
	ckey := backendClusterVersionKey()

	tx := be.BatchTx()
	tx.Lock()
	defer tx.Unlock()
	tx.UnsafePut(clusterBucketName, ckey, []byte(ver.String()))
}

func mustCreateBackendBuckets(be backend.Backend) {
	tx := be.BatchTx()
	tx.Lock()
	defer tx.Unlock()
	tx.UnsafeCreateBucket(membersBucketName)
	tx.UnsafeCreateBucket(membersRemovedBuckedName)
	tx.UnsafeCreateBucket(clusterBucketName)
}

func mustDeleteMemberFromBackend(be backend.Backend, id types.ID) {
	mkey := backendMemberKey(id)

	tx := be.BatchTx()
	tx.Lock()
	tx.UnsafeDelete(membersBucketName, mkey)
	tx.UnsafePut(membersRemovedBuckedName, mkey, []byte("removed"))
	tx.Unlock()
}

func mustSaveMemberToBackend(be backend.Backend, m *Member) {
	mkey := backendMemberKey(m.ID)
	mvalue, err := json.Marshal(m)
	if err != nil {
		plog.Panicf("marshal raftAttributes should never fail: %v", err)
	}

	tx := be.BatchTx()
	tx.Lock()
	tx.UnsafePut(membersBucketName, mkey, mvalue)
	tx.Unlock()
}

func (l Lease) persistTo(b backend.Backend) {
	key := int64ToBytes(int64(l.ID))

	lpb := leasepb.Lease{ID: int64(l.ID), TTL: int64(l.TTL)}
	val, err := lpb.Marshal()
	if err != nil {
		panic("failed to marshal lease proto item")
	}

	b.BatchTx().Lock()
	b.BatchTx().UnsafePut(leaseBucketName, key, val)
	b.BatchTx().Unlock()
}

func WriteKV(be backend.Backend, kv mvccpb.KeyValue) {
	ibytes := newRevBytes()
	revToBytes(revision{main: kv.ModRevision}, ibytes)

	d, err := kv.Marshal()
	if err != nil {
		plog.Fatalf("cannot marshal event: %v", err)
	}

	be.BatchTx().Lock()
	be.BatchTx().UnsafePut(keyBucketName, ibytes, d)
	be.BatchTx().Unlock()
}

func NewAuthStore(be backend.Backend) *authStore {
	tx := be.BatchTx()
	tx.Lock()

	tx.UnsafeCreateBucket(authBucketName)
	tx.UnsafeCreateBucket(authUsersBucketName)
	tx.UnsafeCreateBucket(authRolesBucketName)

	tx.Unlock()
	be.ForceCommit()

	return &authStore{
		be: be,
	}
}

func NewAuthStore(be backend.Backend) *authStore {
	tx := be.BatchTx()
	tx.Lock()

	tx.UnsafeCreateBucket(authBucketName)
	tx.UnsafeCreateBucket(authUsersBucketName)
	tx.UnsafeCreateBucket(authRolesBucketName)

	tx.Unlock()
	be.ForceCommit()

	return &authStore{
		be:           be,
		simpleTokens: make(map[string]string),
	}
}

func (as *authStore) Recover(be backend.Backend) {
	enabled := false
	as.be = be
	tx := be.BatchTx()
	tx.Lock()
	_, vs := tx.UnsafeRange(authBucketName, enableFlagKey, nil, 0)
	if len(vs) == 1 {
		if bytes.Equal(vs[0], authEnabled) {
			enabled = true
		}
	}
	tx.Unlock()

	as.enabledMu.Lock()
	as.enabled = enabled
	as.enabledMu.Unlock()
}

func (s *store) Restore(b backend.Backend) error {
	s.mu.Lock()
	defer s.mu.Unlock()

	close(s.stopc)
	s.fifoSched.Stop()

	s.b = b
	s.kvindex = newTreeIndex()
	s.currentRev = revision{main: 1}
	s.compactMainRev = -1
	s.tx = b.BatchTx()
	s.txnID = -1
	s.fifoSched = schedule.NewFIFOScheduler()
	s.stopc = make(chan struct{})

	return s.restore()
}

func UpdateConsistentIndex(be backend.Backend, index uint64) {
	tx := be.BatchTx()
	tx.Lock()
	defer tx.Unlock()

	var oldi uint64
	_, vs := tx.UnsafeRange(metaBucketName, consistentIndexKeyName, nil, 0)
	if len(vs) != 0 {
		oldi = binary.BigEndian.Uint64(vs[0])
	}

	if index <= oldi {
		return
	}

	bs := make([]byte, 8)
	binary.BigEndian.PutUint64(bs, index)
	tx.UnsafePut(metaBucketName, consistentIndexKeyName, bs)
}

func prepareBackend() backend.Backend {
	var be backend.Backend

	bch := make(chan struct{})
	dbpath := path.Join(migrateDatadir, "member", "snap", "db")
	go func() {
		defer close(bch)
		be = backend.New(dbpath, time.Second, 10000)

	}()
	select {
	case <-bch:
	case <-time.After(time.Second):
		fmt.Fprintf(os.Stderr, "waiting for etcd to close and release its lock on %q\n", dbpath)
		<-bch
	}

	tx := be.BatchTx()
	tx.Lock()
	tx.UnsafeCreateBucket([]byte("key"))
	tx.UnsafeCreateBucket([]byte("meta"))
	tx.Unlock()
	return be
}

// NewServer creates a new EtcdServer from the supplied configuration. The
// configuration is considered static for the lifetime of the EtcdServer.
func NewServer(cfg *ServerConfig) (srv *EtcdServer, err error) {
	st := store.New(StoreClusterPrefix, StoreKeysPrefix)

	var (
		w  *wal.WAL
		n  raft.Node
		s  *raft.MemoryStorage
		id types.ID
		cl *membership.RaftCluster
	)

	if terr := fileutil.TouchDirAll(cfg.DataDir); terr != nil {
		return nil, fmt.Errorf("cannot access data directory: %v", terr)
	}

	haveWAL := wal.Exist(cfg.WALDir())

	if err = fileutil.TouchDirAll(cfg.SnapDir()); err != nil {
		plog.Fatalf("create snapshot directory error: %v", err)
	}
	ss := snap.New(cfg.SnapDir())

	bepath := path.Join(cfg.SnapDir(), databaseFilename)
	beExist := fileutil.Exist(bepath)

	var be backend.Backend
	beOpened := make(chan struct{})
	go func() {
		be = backend.NewDefaultBackend(bepath)
		beOpened <- struct{}{}
	}()

	select {
	case <-beOpened:
	case <-time.After(time.Second):
		plog.Warningf("another etcd process is running with the same data dir and holding the file lock.")
		plog.Warningf("waiting for it to exit before starting...")
		<-beOpened
	}

	defer func() {
		if err != nil {
			be.Close()
		}
	}()

	prt, err := rafthttp.NewRoundTripper(cfg.PeerTLSInfo, cfg.peerDialTimeout())
	if err != nil {
		return nil, err
	}
	var (
		remotes  []*membership.Member
		snapshot *raftpb.Snapshot
	)

	switch {
	case !haveWAL && !cfg.NewCluster:
		if err = cfg.VerifyJoinExisting(); err != nil {
			return nil, err
		}
		cl, err = membership.NewClusterFromURLsMap(cfg.InitialClusterToken, cfg.InitialPeerURLsMap)
		if err != nil {
			return nil, err
		}
		existingCluster, gerr := GetClusterFromRemotePeers(getRemotePeerURLs(cl, cfg.Name), prt)
		if gerr != nil {
			return nil, fmt.Errorf("cannot fetch cluster info from peer urls: %v", gerr)
		}
		if err = membership.ValidateClusterAndAssignIDs(cl, existingCluster); err != nil {
			return nil, fmt.Errorf("error validating peerURLs %s: %v", existingCluster, err)
		}
		if !isCompatibleWithCluster(cl, cl.MemberByName(cfg.Name).ID, prt) {
			return nil, fmt.Errorf("incompatible with current running cluster")
		}

		remotes = existingCluster.Members()
		cl.SetID(existingCluster.ID())
		cl.SetStore(st)
		cl.SetBackend(be)
		cfg.Print()
		id, n, s, w = startNode(cfg, cl, nil)
	case !haveWAL && cfg.NewCluster:
		if err = cfg.VerifyBootstrap(); err != nil {
			return nil, err
		}
		cl, err = membership.NewClusterFromURLsMap(cfg.InitialClusterToken, cfg.InitialPeerURLsMap)
		if err != nil {
			return nil, err
		}
		m := cl.MemberByName(cfg.Name)
		if isMemberBootstrapped(cl, cfg.Name, prt, cfg.bootstrapTimeout()) {
			return nil, fmt.Errorf("member %s has already been bootstrapped", m.ID)
		}
		if cfg.ShouldDiscover() {
			var str string
			str, err = discovery.JoinCluster(cfg.DiscoveryURL, cfg.DiscoveryProxy, m.ID, cfg.InitialPeerURLsMap.String())
			if err != nil {
				return nil, &DiscoveryError{Op: "join", Err: err}
//.........这里部分代码省略.........

func cleanup(s KV, b backend.Backend, path string) {
	s.Close()
	b.Close()
	os.Remove(path)
}