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// 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
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// See the License for the specific language governing permissions and
// limitations under the License.
package mvcc
import "encoding/binary"
// revBytesLen is the byte length of a normal revision.
// First 8 bytes is the revision.main in big-endian format. The 9th byte
// is a '_'. The last 8 bytes is the revision.sub in big-endian format.
const revBytesLen = 8 + 1 + 8
// A revision indicates modification of the key-value space.
// The set of changes that share same main revision changes the key-value space atomically.
type revision struct {
// main is the main revision of a set of changes that happen atomically.
main int64
// sub is the the sub revision of a change in a set of changes that happen
// atomically. Each change has different increasing sub revision in that
// set.
sub int64
func (a revision) GreaterThan(b revision) bool {
if a.main > b.main {
return true
if a.main < b.main {
return false
return a.sub > b.sub
func newRevBytes() []byte {
return make([]byte, revBytesLen, markedRevBytesLen)
func revToBytes(rev revision, bytes []byte) {
binary.BigEndian.PutUint64(bytes, uint64(rev.main))
bytes[8] = '_'
binary.BigEndian.PutUint64(bytes[9:], uint64(rev.sub))
func bytesToRev(bytes []byte) revision {
return revision{
main: int64(binary.BigEndian.Uint64(bytes[0:8])),
sub: int64(binary.BigEndian.Uint64(bytes[9:])),
type revisions []revision
func (a revisions) Len() int { return len(a) }
func (a revisions) Less(i, j int) bool { return a[j].GreaterThan(a[i]) }
func (a revisions) Swap(i, j int) { a[i], a[j] = a[j], a[i] }