mirror of
https://github.com/etcd-io/etcd.git
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123 lines
3.3 KiB
Go
123 lines
3.3 KiB
Go
// Copyright 2015 The etcd Authors
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package mvcc
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import (
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"encoding/binary"
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"fmt"
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)
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const (
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// revBytesLen is the byte length of a normal revision.
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// First 8 bytes is the revision.main in big-endian format. The 9th byte
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// is a '_'. The last 8 bytes is the revision.sub in big-endian format.
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revBytesLen = 8 + 1 + 8
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// markedRevBytesLen is the byte length of marked revision.
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// The first `revBytesLen` bytes represents a normal revision. The last
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// one byte is the mark.
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markedRevBytesLen = revBytesLen + 1
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markBytePosition = markedRevBytesLen - 1
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markTombstone byte = 't'
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)
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type Revision struct {
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// Main is the main revision of a set of changes that happen atomically.
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Main int64
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// Sub is the sub revision of a change in a set of changes that happen
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// atomically. Each change has different increasing sub revision in that
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// set.
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Sub int64
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}
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func (a Revision) GreaterThan(b Revision) bool {
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if a.Main > b.Main {
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return true
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}
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if a.Main < b.Main {
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return false
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}
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return a.Sub > b.Sub
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}
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func RevToBytes(rev Revision, bytes []byte) []byte {
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return BucketKeyToBytes(newBucketKey(rev.Main, rev.Sub, false), bytes)
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}
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func BytesToRev(bytes []byte) Revision {
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return BytesToBucketKey(bytes).Revision
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}
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// BucketKey indicates modification of the key-value space.
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// The set of changes that share same main revision changes the key-value space atomically.
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type BucketKey struct {
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Revision
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tombstone bool
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}
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func newBucketKey(main, sub int64, isTombstone bool) BucketKey {
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return BucketKey{
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Revision: Revision{
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Main: main,
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Sub: sub,
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},
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tombstone: isTombstone,
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}
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}
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func NewRevBytes() []byte {
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return make([]byte, revBytesLen, markedRevBytesLen)
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}
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func BucketKeyToBytes(rev BucketKey, bytes []byte) []byte {
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binary.BigEndian.PutUint64(bytes, uint64(rev.Main))
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bytes[8] = '_'
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binary.BigEndian.PutUint64(bytes[9:], uint64(rev.Sub))
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if rev.tombstone {
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switch len(bytes) {
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case revBytesLen:
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bytes = append(bytes, markTombstone)
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case markedRevBytesLen:
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bytes[markBytePosition] = markTombstone
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}
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}
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return bytes
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}
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func BytesToBucketKey(bytes []byte) BucketKey {
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if (len(bytes) != revBytesLen) && (len(bytes) != markedRevBytesLen) {
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panic(fmt.Sprintf("invalid revision length: %d", len(bytes)))
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}
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if bytes[8] != '_' {
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panic(fmt.Sprintf("invalid separator in bucket key: %q", bytes[8]))
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}
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main := int64(binary.BigEndian.Uint64(bytes[0:8]))
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sub := int64(binary.BigEndian.Uint64(bytes[9:]))
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if main < 0 || sub < 0 {
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panic(fmt.Sprintf("negative revision: main=%d sub=%d", main, sub))
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}
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return BucketKey{
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Revision: Revision{
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Main: main,
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Sub: sub,
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},
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tombstone: isTombstone(bytes),
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}
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}
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// isTombstone checks whether the revision bytes is a tombstone.
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func isTombstone(b []byte) bool {
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return len(b) == markedRevBytesLen && b[markBytePosition] == markTombstone
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}
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