diff --git a/vendor/go.etcd.io/etcd/raft/log_unstable.go b/vendor/go.etcd.io/etcd/raft/log_unstable.go
new file mode 100644
index 0000000..1005bf6
--- /dev/null
+++ b/vendor/go.etcd.io/etcd/raft/log_unstable.go
@@ -0,0 +1,159 @@
+// 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 raft
+
+import pb "go.etcd.io/etcd/raft/raftpb"
+
+// unstable.entries[i] has raft log position i+unstable.offset.
+// Note that unstable.offset may be less than the highest log
+// position in storage; this means that the next write to storage
+// might need to truncate the log before persisting unstable.entries.
+type unstable struct {
+	// the incoming unstable snapshot, if any.
+	snapshot *pb.Snapshot
+	// all entries that have not yet been written to storage.
+	entries []pb.Entry
+	offset  uint64
+
+	logger Logger
+}
+
+// maybeFirstIndex returns the index of the first possible entry in entries
+// if it has a snapshot.
+func (u *unstable) maybeFirstIndex() (uint64, bool) {
+	if u.snapshot != nil {
+		return u.snapshot.Metadata.Index + 1, true
+	}
+	return 0, false
+}
+
+// maybeLastIndex returns the last index if it has at least one
+// unstable entry or snapshot.
+func (u *unstable) maybeLastIndex() (uint64, bool) {
+	if l := len(u.entries); l != 0 {
+		return u.offset + uint64(l) - 1, true
+	}
+	if u.snapshot != nil {
+		return u.snapshot.Metadata.Index, true
+	}
+	return 0, false
+}
+
+// maybeTerm returns the term of the entry at index i, if there
+// is any.
+func (u *unstable) maybeTerm(i uint64) (uint64, bool) {
+	if i < u.offset {
+		if u.snapshot == nil {
+			return 0, false
+		}
+		if u.snapshot.Metadata.Index == i {
+			return u.snapshot.Metadata.Term, true
+		}
+		return 0, false
+	}
+
+	last, ok := u.maybeLastIndex()
+	if !ok {
+		return 0, false
+	}
+	if i > last {
+		return 0, false
+	}
+	return u.entries[i-u.offset].Term, true
+}
+
+func (u *unstable) stableTo(i, t uint64) {
+	gt, ok := u.maybeTerm(i)
+	if !ok {
+		return
+	}
+	// if i < offset, term is matched with the snapshot
+	// only update the unstable entries if term is matched with
+	// an unstable entry.
+	if gt == t && i >= u.offset {
+		u.entries = u.entries[i+1-u.offset:]
+		u.offset = i + 1
+		u.shrinkEntriesArray()
+	}
+}
+
+// shrinkEntriesArray discards the underlying array used by the entries slice
+// if most of it isn't being used. This avoids holding references to a bunch of
+// potentially large entries that aren't needed anymore. Simply clearing the
+// entries wouldn't be safe because clients might still be using them.
+func (u *unstable) shrinkEntriesArray() {
+	// We replace the array if we're using less than half of the space in
+	// it. This number is fairly arbitrary, chosen as an attempt to balance
+	// memory usage vs number of allocations. It could probably be improved
+	// with some focused tuning.
+	const lenMultiple = 2
+	if len(u.entries) == 0 {
+		u.entries = nil
+	} else if len(u.entries)*lenMultiple < cap(u.entries) {
+		newEntries := make([]pb.Entry, len(u.entries))
+		copy(newEntries, u.entries)
+		u.entries = newEntries
+	}
+}
+
+func (u *unstable) stableSnapTo(i uint64) {
+	if u.snapshot != nil && u.snapshot.Metadata.Index == i {
+		u.snapshot = nil
+	}
+}
+
+func (u *unstable) restore(s pb.Snapshot) {
+	u.offset = s.Metadata.Index + 1
+	u.entries = nil
+	u.snapshot = &s
+}
+
+func (u *unstable) truncateAndAppend(ents []pb.Entry) {
+	after := ents[0].Index
+	switch {
+	case after == u.offset+uint64(len(u.entries)):
+		// after is the next index in the u.entries
+		// directly append
+		u.entries = append(u.entries, ents...)
+	case after <= u.offset:
+		u.logger.Infof("replace the unstable entries from index %d", after)
+		// The log is being truncated to before our current offset
+		// portion, so set the offset and replace the entries
+		u.offset = after
+		u.entries = ents
+	default:
+		// truncate to after and copy to u.entries
+		// then append
+		u.logger.Infof("truncate the unstable entries before index %d", after)
+		u.entries = append([]pb.Entry{}, u.slice(u.offset, after)...)
+		u.entries = append(u.entries, ents...)
+	}
+}
+
+func (u *unstable) slice(lo uint64, hi uint64) []pb.Entry {
+	u.mustCheckOutOfBounds(lo, hi)
+	return u.entries[lo-u.offset : hi-u.offset]
+}
+
+// u.offset <= lo <= hi <= u.offset+len(u.entries)
+func (u *unstable) mustCheckOutOfBounds(lo, hi uint64) {
+	if lo > hi {
+		u.logger.Panicf("invalid unstable.slice %d > %d", lo, hi)
+	}
+	upper := u.offset + uint64(len(u.entries))
+	if lo < u.offset || hi > upper {
+		u.logger.Panicf("unstable.slice[%d,%d) out of bound [%d,%d]", lo, hi, u.offset, upper)
+	}
+}