diff --git a/vendor/github.com/coreos/etcd/mvcc/index.go b/vendor/github.com/coreos/etcd/mvcc/index.go
new file mode 100644
index 0000000..b27a9e5
--- /dev/null
+++ b/vendor/github.com/coreos/etcd/mvcc/index.go
@@ -0,0 +1,251 @@
+// 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 mvcc
+
+import (
+	"sort"
+	"sync"
+
+	"github.com/google/btree"
+)
+
+type index interface {
+	Get(key []byte, atRev int64) (rev, created revision, ver int64, err error)
+	Range(key, end []byte, atRev int64) ([][]byte, []revision)
+	Revisions(key, end []byte, atRev int64) []revision
+	Put(key []byte, rev revision)
+	Tombstone(key []byte, rev revision) error
+	RangeSince(key, end []byte, rev int64) []revision
+	Compact(rev int64) map[revision]struct{}
+	Keep(rev int64) map[revision]struct{}
+	Equal(b index) bool
+
+	Insert(ki *keyIndex)
+	KeyIndex(ki *keyIndex) *keyIndex
+}
+
+type treeIndex struct {
+	sync.RWMutex
+	tree *btree.BTree
+}
+
+func newTreeIndex() index {
+	return &treeIndex{
+		tree: btree.New(32),
+	}
+}
+
+func (ti *treeIndex) Put(key []byte, rev revision) {
+	keyi := &keyIndex{key: key}
+
+	ti.Lock()
+	defer ti.Unlock()
+	item := ti.tree.Get(keyi)
+	if item == nil {
+		keyi.put(rev.main, rev.sub)
+		ti.tree.ReplaceOrInsert(keyi)
+		return
+	}
+	okeyi := item.(*keyIndex)
+	okeyi.put(rev.main, rev.sub)
+}
+
+func (ti *treeIndex) Get(key []byte, atRev int64) (modified, created revision, ver int64, err error) {
+	keyi := &keyIndex{key: key}
+	ti.RLock()
+	defer ti.RUnlock()
+	if keyi = ti.keyIndex(keyi); keyi == nil {
+		return revision{}, revision{}, 0, ErrRevisionNotFound
+	}
+	return keyi.get(atRev)
+}
+
+func (ti *treeIndex) KeyIndex(keyi *keyIndex) *keyIndex {
+	ti.RLock()
+	defer ti.RUnlock()
+	return ti.keyIndex(keyi)
+}
+
+func (ti *treeIndex) keyIndex(keyi *keyIndex) *keyIndex {
+	if item := ti.tree.Get(keyi); item != nil {
+		return item.(*keyIndex)
+	}
+	return nil
+}
+
+func (ti *treeIndex) visit(key, end []byte, f func(ki *keyIndex)) {
+	keyi, endi := &keyIndex{key: key}, &keyIndex{key: end}
+
+	ti.RLock()
+	defer ti.RUnlock()
+
+	ti.tree.AscendGreaterOrEqual(keyi, func(item btree.Item) bool {
+		if len(endi.key) > 0 && !item.Less(endi) {
+			return false
+		}
+		f(item.(*keyIndex))
+		return true
+	})
+}
+
+func (ti *treeIndex) Revisions(key, end []byte, atRev int64) (revs []revision) {
+	if end == nil {
+		rev, _, _, err := ti.Get(key, atRev)
+		if err != nil {
+			return nil
+		}
+		return []revision{rev}
+	}
+	ti.visit(key, end, func(ki *keyIndex) {
+		if rev, _, _, err := ki.get(atRev); err == nil {
+			revs = append(revs, rev)
+		}
+	})
+	return revs
+}
+
+func (ti *treeIndex) Range(key, end []byte, atRev int64) (keys [][]byte, revs []revision) {
+	if end == nil {
+		rev, _, _, err := ti.Get(key, atRev)
+		if err != nil {
+			return nil, nil
+		}
+		return [][]byte{key}, []revision{rev}
+	}
+	ti.visit(key, end, func(ki *keyIndex) {
+		if rev, _, _, err := ki.get(atRev); err == nil {
+			revs = append(revs, rev)
+			keys = append(keys, ki.key)
+		}
+	})
+	return keys, revs
+}
+
+func (ti *treeIndex) Tombstone(key []byte, rev revision) error {
+	keyi := &keyIndex{key: key}
+
+	ti.Lock()
+	defer ti.Unlock()
+	item := ti.tree.Get(keyi)
+	if item == nil {
+		return ErrRevisionNotFound
+	}
+
+	ki := item.(*keyIndex)
+	return ki.tombstone(rev.main, rev.sub)
+}
+
+// RangeSince returns all revisions from key(including) to end(excluding)
+// at or after the given rev. The returned slice is sorted in the order
+// of revision.
+func (ti *treeIndex) RangeSince(key, end []byte, rev int64) []revision {
+	keyi := &keyIndex{key: key}
+
+	ti.RLock()
+	defer ti.RUnlock()
+
+	if end == nil {
+		item := ti.tree.Get(keyi)
+		if item == nil {
+			return nil
+		}
+		keyi = item.(*keyIndex)
+		return keyi.since(rev)
+	}
+
+	endi := &keyIndex{key: end}
+	var revs []revision
+	ti.tree.AscendGreaterOrEqual(keyi, func(item btree.Item) bool {
+		if len(endi.key) > 0 && !item.Less(endi) {
+			return false
+		}
+		curKeyi := item.(*keyIndex)
+		revs = append(revs, curKeyi.since(rev)...)
+		return true
+	})
+	sort.Sort(revisions(revs))
+
+	return revs
+}
+
+func (ti *treeIndex) Compact(rev int64) map[revision]struct{} {
+	available := make(map[revision]struct{})
+	var emptyki []*keyIndex
+	plog.Printf("store.index: compact %d", rev)
+	// TODO: do not hold the lock for long time?
+	// This is probably OK. Compacting 10M keys takes O(10ms).
+	ti.Lock()
+	defer ti.Unlock()
+	ti.tree.Ascend(compactIndex(rev, available, &emptyki))
+	for _, ki := range emptyki {
+		item := ti.tree.Delete(ki)
+		if item == nil {
+			plog.Panic("store.index: unexpected delete failure during compaction")
+		}
+	}
+	return available
+}
+
+// Keep finds all revisions to be kept for a Compaction at the given rev.
+func (ti *treeIndex) Keep(rev int64) map[revision]struct{} {
+	available := make(map[revision]struct{})
+	ti.RLock()
+	defer ti.RUnlock()
+	ti.tree.Ascend(func(i btree.Item) bool {
+		keyi := i.(*keyIndex)
+		keyi.keep(rev, available)
+		return true
+	})
+	return available
+}
+
+func compactIndex(rev int64, available map[revision]struct{}, emptyki *[]*keyIndex) func(i btree.Item) bool {
+	return func(i btree.Item) bool {
+		keyi := i.(*keyIndex)
+		keyi.compact(rev, available)
+		if keyi.isEmpty() {
+			*emptyki = append(*emptyki, keyi)
+		}
+		return true
+	}
+}
+
+func (ti *treeIndex) Equal(bi index) bool {
+	b := bi.(*treeIndex)
+
+	if ti.tree.Len() != b.tree.Len() {
+		return false
+	}
+
+	equal := true
+
+	ti.tree.Ascend(func(item btree.Item) bool {
+		aki := item.(*keyIndex)
+		bki := b.tree.Get(item).(*keyIndex)
+		if !aki.equal(bki) {
+			equal = false
+			return false
+		}
+		return true
+	})
+
+	return equal
+}
+
+func (ti *treeIndex) Insert(ki *keyIndex) {
+	ti.Lock()
+	defer ti.Unlock()
+	ti.tree.ReplaceOrInsert(ki)
+}