diff --git a/vendor/go.etcd.io/etcd/mvcc/backend/backend.go b/vendor/go.etcd.io/etcd/mvcc/backend/backend.go
new file mode 100644
index 0000000..bffd749
--- /dev/null
+++ b/vendor/go.etcd.io/etcd/mvcc/backend/backend.go
@@ -0,0 +1,570 @@
+// Copyright 2015 The etcd Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package backend
+
+import (
+	"fmt"
+	"hash/crc32"
+	"io"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"sync"
+	"sync/atomic"
+	"time"
+
+	"github.com/coreos/pkg/capnslog"
+	humanize "github.com/dustin/go-humanize"
+	bolt "go.etcd.io/bbolt"
+	"go.uber.org/zap"
+)
+
+var (
+	defaultBatchLimit    = 10000
+	defaultBatchInterval = 100 * time.Millisecond
+
+	defragLimit = 10000
+
+	// initialMmapSize is the initial size of the mmapped region. Setting this larger than
+	// the potential max db size can prevent writer from blocking reader.
+	// This only works for linux.
+	initialMmapSize = uint64(10 * 1024 * 1024 * 1024)
+
+	plog = capnslog.NewPackageLogger("go.etcd.io/etcd", "mvcc/backend")
+
+	// minSnapshotWarningTimeout is the minimum threshold to trigger a long running snapshot warning.
+	minSnapshotWarningTimeout = 30 * time.Second
+)
+
+type Backend interface {
+	// ReadTx returns a read transaction. It is replaced by ConcurrentReadTx in the main data path, see #10523.
+	ReadTx() ReadTx
+	BatchTx() BatchTx
+	// ConcurrentReadTx returns a non-blocking read transaction.
+	ConcurrentReadTx() ReadTx
+
+	Snapshot() Snapshot
+	Hash(ignores map[IgnoreKey]struct{}) (uint32, error)
+	// Size returns the current size of the backend physically allocated.
+	// The backend can hold DB space that is not utilized at the moment,
+	// since it can conduct pre-allocation or spare unused space for recycling.
+	// Use SizeInUse() instead for the actual DB size.
+	Size() int64
+	// SizeInUse returns the current size of the backend logically in use.
+	// Since the backend can manage free space in a non-byte unit such as
+	// number of pages, the returned value can be not exactly accurate in bytes.
+	SizeInUse() int64
+	// OpenReadTxN returns the number of currently open read transactions in the backend.
+	OpenReadTxN() int64
+	Defrag() error
+	ForceCommit()
+	Close() error
+}
+
+type Snapshot interface {
+	// Size gets the size of the snapshot.
+	Size() int64
+	// WriteTo writes the snapshot into the given writer.
+	WriteTo(w io.Writer) (n int64, err error)
+	// Close closes the snapshot.
+	Close() error
+}
+
+type backend struct {
+	// size and commits are used with atomic operations so they must be
+	// 64-bit aligned, otherwise 32-bit tests will crash
+
+	// size is the number of bytes allocated in the backend
+	size int64
+	// sizeInUse is the number of bytes actually used in the backend
+	sizeInUse int64
+	// commits counts number of commits since start
+	commits int64
+	// openReadTxN is the number of currently open read transactions in the backend
+	openReadTxN int64
+
+	mu sync.RWMutex
+	db *bolt.DB
+
+	batchInterval time.Duration
+	batchLimit    int
+	batchTx       *batchTxBuffered
+
+	readTx *readTx
+
+	stopc chan struct{}
+	donec chan struct{}
+
+	lg *zap.Logger
+}
+
+type BackendConfig struct {
+	// Path is the file path to the backend file.
+	Path string
+	// BatchInterval is the maximum time before flushing the BatchTx.
+	BatchInterval time.Duration
+	// BatchLimit is the maximum puts before flushing the BatchTx.
+	BatchLimit int
+	// BackendFreelistType is the backend boltdb's freelist type.
+	BackendFreelistType bolt.FreelistType
+	// MmapSize is the number of bytes to mmap for the backend.
+	MmapSize uint64
+	// Logger logs backend-side operations.
+	Logger *zap.Logger
+}
+
+func DefaultBackendConfig() BackendConfig {
+	return BackendConfig{
+		BatchInterval: defaultBatchInterval,
+		BatchLimit:    defaultBatchLimit,
+		MmapSize:      initialMmapSize,
+	}
+}
+
+func New(bcfg BackendConfig) Backend {
+	return newBackend(bcfg)
+}
+
+func NewDefaultBackend(path string) Backend {
+	bcfg := DefaultBackendConfig()
+	bcfg.Path = path
+	return newBackend(bcfg)
+}
+
+func newBackend(bcfg BackendConfig) *backend {
+	bopts := &bolt.Options{}
+	if boltOpenOptions != nil {
+		*bopts = *boltOpenOptions
+	}
+	bopts.InitialMmapSize = bcfg.mmapSize()
+	bopts.FreelistType = bcfg.BackendFreelistType
+
+	db, err := bolt.Open(bcfg.Path, 0600, bopts)
+	if err != nil {
+		if bcfg.Logger != nil {
+			bcfg.Logger.Panic("failed to open database", zap.String("path", bcfg.Path), zap.Error(err))
+		} else {
+			plog.Panicf("cannot open database at %s (%v)", bcfg.Path, err)
+		}
+	}
+
+	// In future, may want to make buffering optional for low-concurrency systems
+	// or dynamically swap between buffered/non-buffered depending on workload.
+	b := &backend{
+		db: db,
+
+		batchInterval: bcfg.BatchInterval,
+		batchLimit:    bcfg.BatchLimit,
+
+		readTx: &readTx{
+			buf: txReadBuffer{
+				txBuffer: txBuffer{make(map[string]*bucketBuffer)},
+			},
+			buckets: make(map[string]*bolt.Bucket),
+			txWg:    new(sync.WaitGroup),
+		},
+
+		stopc: make(chan struct{}),
+		donec: make(chan struct{}),
+
+		lg: bcfg.Logger,
+	}
+	b.batchTx = newBatchTxBuffered(b)
+	go b.run()
+	return b
+}
+
+// BatchTx returns the current batch tx in coalescer. The tx can be used for read and
+// write operations. The write result can be retrieved within the same tx immediately.
+// The write result is isolated with other txs until the current one get committed.
+func (b *backend) BatchTx() BatchTx {
+	return b.batchTx
+}
+
+func (b *backend) ReadTx() ReadTx { return b.readTx }
+
+// ConcurrentReadTx creates and returns a new ReadTx, which:
+// A) creates and keeps a copy of backend.readTx.txReadBuffer,
+// B) references the boltdb read Tx (and its bucket cache) of current batch interval.
+func (b *backend) ConcurrentReadTx() ReadTx {
+	b.readTx.RLock()
+	defer b.readTx.RUnlock()
+	// prevent boltdb read Tx from been rolled back until store read Tx is done. Needs to be called when holding readTx.RLock().
+	b.readTx.txWg.Add(1)
+	// TODO: might want to copy the read buffer lazily - create copy when A) end of a write transaction B) end of a batch interval.
+	return &concurrentReadTx{
+		buf:     b.readTx.buf.unsafeCopy(),
+		tx:      b.readTx.tx,
+		txMu:    &b.readTx.txMu,
+		buckets: b.readTx.buckets,
+		txWg:    b.readTx.txWg,
+	}
+}
+
+// ForceCommit forces the current batching tx to commit.
+func (b *backend) ForceCommit() {
+	b.batchTx.Commit()
+}
+
+func (b *backend) Snapshot() Snapshot {
+	b.batchTx.Commit()
+
+	b.mu.RLock()
+	defer b.mu.RUnlock()
+	tx, err := b.db.Begin(false)
+	if err != nil {
+		if b.lg != nil {
+			b.lg.Fatal("failed to begin tx", zap.Error(err))
+		} else {
+			plog.Fatalf("cannot begin tx (%s)", err)
+		}
+	}
+
+	stopc, donec := make(chan struct{}), make(chan struct{})
+	dbBytes := tx.Size()
+	go func() {
+		defer close(donec)
+		// sendRateBytes is based on transferring snapshot data over a 1 gigabit/s connection
+		// assuming a min tcp throughput of 100MB/s.
+		var sendRateBytes int64 = 100 * 1024 * 1014
+		warningTimeout := time.Duration(int64((float64(dbBytes) / float64(sendRateBytes)) * float64(time.Second)))
+		if warningTimeout < minSnapshotWarningTimeout {
+			warningTimeout = minSnapshotWarningTimeout
+		}
+		start := time.Now()
+		ticker := time.NewTicker(warningTimeout)
+		defer ticker.Stop()
+		for {
+			select {
+			case <-ticker.C:
+				if b.lg != nil {
+					b.lg.Warn(
+						"snapshotting taking too long to transfer",
+						zap.Duration("taking", time.Since(start)),
+						zap.Int64("bytes", dbBytes),
+						zap.String("size", humanize.Bytes(uint64(dbBytes))),
+					)
+				} else {
+					plog.Warningf("snapshotting is taking more than %v seconds to finish transferring %v MB [started at %v]", time.Since(start).Seconds(), float64(dbBytes)/float64(1024*1014), start)
+				}
+
+			case <-stopc:
+				snapshotTransferSec.Observe(time.Since(start).Seconds())
+				return
+			}
+		}
+	}()
+
+	return &snapshot{tx, stopc, donec}
+}
+
+type IgnoreKey struct {
+	Bucket string
+	Key    string
+}
+
+func (b *backend) Hash(ignores map[IgnoreKey]struct{}) (uint32, error) {
+	h := crc32.New(crc32.MakeTable(crc32.Castagnoli))
+
+	b.mu.RLock()
+	defer b.mu.RUnlock()
+	err := b.db.View(func(tx *bolt.Tx) error {
+		c := tx.Cursor()
+		for next, _ := c.First(); next != nil; next, _ = c.Next() {
+			b := tx.Bucket(next)
+			if b == nil {
+				return fmt.Errorf("cannot get hash of bucket %s", string(next))
+			}
+			h.Write(next)
+			b.ForEach(func(k, v []byte) error {
+				bk := IgnoreKey{Bucket: string(next), Key: string(k)}
+				if _, ok := ignores[bk]; !ok {
+					h.Write(k)
+					h.Write(v)
+				}
+				return nil
+			})
+		}
+		return nil
+	})
+
+	if err != nil {
+		return 0, err
+	}
+
+	return h.Sum32(), nil
+}
+
+func (b *backend) Size() int64 {
+	return atomic.LoadInt64(&b.size)
+}
+
+func (b *backend) SizeInUse() int64 {
+	return atomic.LoadInt64(&b.sizeInUse)
+}
+
+func (b *backend) run() {
+	defer close(b.donec)
+	t := time.NewTimer(b.batchInterval)
+	defer t.Stop()
+	for {
+		select {
+		case <-t.C:
+		case <-b.stopc:
+			b.batchTx.CommitAndStop()
+			return
+		}
+		if b.batchTx.safePending() != 0 {
+			b.batchTx.Commit()
+		}
+		t.Reset(b.batchInterval)
+	}
+}
+
+func (b *backend) Close() error {
+	close(b.stopc)
+	<-b.donec
+	return b.db.Close()
+}
+
+// Commits returns total number of commits since start
+func (b *backend) Commits() int64 {
+	return atomic.LoadInt64(&b.commits)
+}
+
+func (b *backend) Defrag() error {
+	return b.defrag()
+}
+
+func (b *backend) defrag() error {
+	now := time.Now()
+
+	// TODO: make this non-blocking?
+	// lock batchTx to ensure nobody is using previous tx, and then
+	// close previous ongoing tx.
+	b.batchTx.Lock()
+	defer b.batchTx.Unlock()
+
+	// lock database after lock tx to avoid deadlock.
+	b.mu.Lock()
+	defer b.mu.Unlock()
+
+	// block concurrent read requests while resetting tx
+	b.readTx.Lock()
+	defer b.readTx.Unlock()
+
+	b.batchTx.unsafeCommit(true)
+
+	b.batchTx.tx = nil
+
+	tmpdb, err := bolt.Open(b.db.Path()+".tmp", 0600, boltOpenOptions)
+	if err != nil {
+		return err
+	}
+
+	dbp := b.db.Path()
+	tdbp := tmpdb.Path()
+	size1, sizeInUse1 := b.Size(), b.SizeInUse()
+	if b.lg != nil {
+		b.lg.Info(
+			"defragmenting",
+			zap.String("path", dbp),
+			zap.Int64("current-db-size-bytes", size1),
+			zap.String("current-db-size", humanize.Bytes(uint64(size1))),
+			zap.Int64("current-db-size-in-use-bytes", sizeInUse1),
+			zap.String("current-db-size-in-use", humanize.Bytes(uint64(sizeInUse1))),
+		)
+	}
+
+	err = defragdb(b.db, tmpdb, defragLimit)
+	if err != nil {
+		tmpdb.Close()
+		os.RemoveAll(tmpdb.Path())
+		return err
+	}
+
+	err = b.db.Close()
+	if err != nil {
+		if b.lg != nil {
+			b.lg.Fatal("failed to close database", zap.Error(err))
+		} else {
+			plog.Fatalf("cannot close database (%s)", err)
+		}
+	}
+	err = tmpdb.Close()
+	if err != nil {
+		if b.lg != nil {
+			b.lg.Fatal("failed to close tmp database", zap.Error(err))
+		} else {
+			plog.Fatalf("cannot close database (%s)", err)
+		}
+	}
+	err = os.Rename(tdbp, dbp)
+	if err != nil {
+		if b.lg != nil {
+			b.lg.Fatal("failed to rename tmp database", zap.Error(err))
+		} else {
+			plog.Fatalf("cannot rename database (%s)", err)
+		}
+	}
+
+	b.db, err = bolt.Open(dbp, 0600, boltOpenOptions)
+	if err != nil {
+		if b.lg != nil {
+			b.lg.Fatal("failed to open database", zap.String("path", dbp), zap.Error(err))
+		} else {
+			plog.Panicf("cannot open database at %s (%v)", dbp, err)
+		}
+	}
+	b.batchTx.tx = b.unsafeBegin(true)
+
+	b.readTx.reset()
+	b.readTx.tx = b.unsafeBegin(false)
+
+	size := b.readTx.tx.Size()
+	db := b.readTx.tx.DB()
+	atomic.StoreInt64(&b.size, size)
+	atomic.StoreInt64(&b.sizeInUse, size-(int64(db.Stats().FreePageN)*int64(db.Info().PageSize)))
+
+	took := time.Since(now)
+	defragSec.Observe(took.Seconds())
+
+	size2, sizeInUse2 := b.Size(), b.SizeInUse()
+	if b.lg != nil {
+		b.lg.Info(
+			"defragmented",
+			zap.String("path", dbp),
+			zap.Int64("current-db-size-bytes-diff", size2-size1),
+			zap.Int64("current-db-size-bytes", size2),
+			zap.String("current-db-size", humanize.Bytes(uint64(size2))),
+			zap.Int64("current-db-size-in-use-bytes-diff", sizeInUse2-sizeInUse1),
+			zap.Int64("current-db-size-in-use-bytes", sizeInUse2),
+			zap.String("current-db-size-in-use", humanize.Bytes(uint64(sizeInUse2))),
+			zap.Duration("took", took),
+		)
+	}
+	return nil
+}
+
+func defragdb(odb, tmpdb *bolt.DB, limit int) error {
+	// open a tx on tmpdb for writes
+	tmptx, err := tmpdb.Begin(true)
+	if err != nil {
+		return err
+	}
+
+	// open a tx on old db for read
+	tx, err := odb.Begin(false)
+	if err != nil {
+		return err
+	}
+	defer tx.Rollback()
+
+	c := tx.Cursor()
+
+	count := 0
+	for next, _ := c.First(); next != nil; next, _ = c.Next() {
+		b := tx.Bucket(next)
+		if b == nil {
+			return fmt.Errorf("backend: cannot defrag bucket %s", string(next))
+		}
+
+		tmpb, berr := tmptx.CreateBucketIfNotExists(next)
+		if berr != nil {
+			return berr
+		}
+		tmpb.FillPercent = 0.9 // for seq write in for each
+
+		b.ForEach(func(k, v []byte) error {
+			count++
+			if count > limit {
+				err = tmptx.Commit()
+				if err != nil {
+					return err
+				}
+				tmptx, err = tmpdb.Begin(true)
+				if err != nil {
+					return err
+				}
+				tmpb = tmptx.Bucket(next)
+				tmpb.FillPercent = 0.9 // for seq write in for each
+
+				count = 0
+			}
+			return tmpb.Put(k, v)
+		})
+	}
+
+	return tmptx.Commit()
+}
+
+func (b *backend) begin(write bool) *bolt.Tx {
+	b.mu.RLock()
+	tx := b.unsafeBegin(write)
+	b.mu.RUnlock()
+
+	size := tx.Size()
+	db := tx.DB()
+	stats := db.Stats()
+	atomic.StoreInt64(&b.size, size)
+	atomic.StoreInt64(&b.sizeInUse, size-(int64(stats.FreePageN)*int64(db.Info().PageSize)))
+	atomic.StoreInt64(&b.openReadTxN, int64(stats.OpenTxN))
+
+	return tx
+}
+
+func (b *backend) unsafeBegin(write bool) *bolt.Tx {
+	tx, err := b.db.Begin(write)
+	if err != nil {
+		if b.lg != nil {
+			b.lg.Fatal("failed to begin tx", zap.Error(err))
+		} else {
+			plog.Fatalf("cannot begin tx (%s)", err)
+		}
+	}
+	return tx
+}
+
+func (b *backend) OpenReadTxN() int64 {
+	return atomic.LoadInt64(&b.openReadTxN)
+}
+
+// NewTmpBackend creates a backend implementation for testing.
+func NewTmpBackend(batchInterval time.Duration, batchLimit int) (*backend, string) {
+	dir, err := ioutil.TempDir(os.TempDir(), "etcd_backend_test")
+	if err != nil {
+		panic(err)
+	}
+	tmpPath := filepath.Join(dir, "database")
+	bcfg := DefaultBackendConfig()
+	bcfg.Path, bcfg.BatchInterval, bcfg.BatchLimit = tmpPath, batchInterval, batchLimit
+	return newBackend(bcfg), tmpPath
+}
+
+func NewDefaultTmpBackend() (*backend, string) {
+	return NewTmpBackend(defaultBatchInterval, defaultBatchLimit)
+}
+
+type snapshot struct {
+	*bolt.Tx
+	stopc chan struct{}
+	donec chan struct{}
+}
+
+func (s *snapshot) Close() error {
+	close(s.stopc)
+	<-s.donec
+	return s.Tx.Rollback()
+}