Revision 3fae828623c194feb307c49c15d66dca9366e195 authored by Joe Betz on 10 October 2019, 17:59:40 UTC, committed by Joe Betz on 10 October 2019, 17:59:40 UTC
1 parent 011bd86
key_index.go
// 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 (
"bytes"
"errors"
"fmt"
"github.com/google/btree"
)
var (
ErrRevisionNotFound = errors.New("mvcc: revision not found")
)
// keyIndex stores the revisions of a key in the backend.
// Each keyIndex has at least one key generation.
// Each generation might have several key versions.
// Tombstone on a key appends an tombstone version at the end
// of the current generation and creates a new empty generation.
// Each version of a key has an index pointing to the backend.
//
// For example: put(1.0);put(2.0);tombstone(3.0);put(4.0);tombstone(5.0) on key "foo"
// generate a keyIndex:
// key: "foo"
// rev: 5
// generations:
// {empty}
// {4.0, 5.0(t)}
// {1.0, 2.0, 3.0(t)}
//
// Compact a keyIndex removes the versions with smaller or equal to
// rev except the largest one. If the generation becomes empty
// during compaction, it will be removed. if all the generations get
// removed, the keyIndex should be removed.
//
// For example:
// compact(2) on the previous example
// generations:
// {empty}
// {4.0, 5.0(t)}
// {2.0, 3.0(t)}
//
// compact(4)
// generations:
// {empty}
// {4.0, 5.0(t)}
//
// compact(5):
// generations:
// {empty} -> key SHOULD be removed.
//
// compact(6):
// generations:
// {empty} -> key SHOULD be removed.
type keyIndex struct {
key []byte
modified revision // the main rev of the last modification
generations []generation
}
// put puts a revision to the keyIndex.
func (ki *keyIndex) put(main int64, sub int64) {
rev := revision{main: main, sub: sub}
if !rev.GreaterThan(ki.modified) {
plog.Panicf("store.keyindex: put with unexpected smaller revision [%v / %v]", rev, ki.modified)
}
if len(ki.generations) == 0 {
ki.generations = append(ki.generations, generation{})
}
g := &ki.generations[len(ki.generations)-1]
if len(g.revs) == 0 { // create a new key
keysGauge.Inc()
g.created = rev
}
g.revs = append(g.revs, rev)
g.ver++
ki.modified = rev
}
func (ki *keyIndex) restore(created, modified revision, ver int64) {
if len(ki.generations) != 0 {
plog.Panicf("store.keyindex: cannot restore non-empty keyIndex")
}
ki.modified = modified
g := generation{created: created, ver: ver, revs: []revision{modified}}
ki.generations = append(ki.generations, g)
keysGauge.Inc()
}
// tombstone puts a revision, pointing to a tombstone, to the keyIndex.
// It also creates a new empty generation in the keyIndex.
// It returns ErrRevisionNotFound when tombstone on an empty generation.
func (ki *keyIndex) tombstone(main int64, sub int64) error {
if ki.isEmpty() {
plog.Panicf("store.keyindex: unexpected tombstone on empty keyIndex %s", string(ki.key))
}
if ki.generations[len(ki.generations)-1].isEmpty() {
return ErrRevisionNotFound
}
ki.put(main, sub)
ki.generations = append(ki.generations, generation{})
keysGauge.Dec()
return nil
}
// get gets the modified, created revision and version of the key that satisfies the given atRev.
// Rev must be higher than or equal to the given atRev.
func (ki *keyIndex) get(atRev int64) (modified, created revision, ver int64, err error) {
if ki.isEmpty() {
plog.Panicf("store.keyindex: unexpected get on empty keyIndex %s", string(ki.key))
}
g := ki.findGeneration(atRev)
if g.isEmpty() {
return revision{}, revision{}, 0, ErrRevisionNotFound
}
n := g.walk(func(rev revision) bool { return rev.main > atRev })
if n != -1 {
return g.revs[n], g.created, g.ver - int64(len(g.revs)-n-1), nil
}
return revision{}, revision{}, 0, ErrRevisionNotFound
}
// since returns revisions since the given rev. Only the revision with the
// largest sub revision will be returned if multiple revisions have the same
// main revision.
func (ki *keyIndex) since(rev int64) []revision {
if ki.isEmpty() {
plog.Panicf("store.keyindex: unexpected get on empty keyIndex %s", string(ki.key))
}
since := revision{rev, 0}
var gi int
// find the generations to start checking
for gi = len(ki.generations) - 1; gi > 0; gi-- {
g := ki.generations[gi]
if g.isEmpty() {
continue
}
if since.GreaterThan(g.created) {
break
}
}
var revs []revision
var last int64
for ; gi < len(ki.generations); gi++ {
for _, r := range ki.generations[gi].revs {
if since.GreaterThan(r) {
continue
}
if r.main == last {
// replace the revision with a new one that has higher sub value,
// because the original one should not be seen by external
revs[len(revs)-1] = r
continue
}
revs = append(revs, r)
last = r.main
}
}
return revs
}
// compact compacts a keyIndex by removing the versions with smaller or equal
// revision than the given atRev except the largest one (If the largest one is
// a tombstone, it will not be kept).
// If a generation becomes empty during compaction, it will be removed.
func (ki *keyIndex) compact(atRev int64, available map[revision]struct{}) {
if ki.isEmpty() {
plog.Panicf("store.keyindex: unexpected compact on empty keyIndex %s", string(ki.key))
}
genIdx, revIndex := ki.doCompact(atRev, available)
g := &ki.generations[genIdx]
if !g.isEmpty() {
// remove the previous contents.
if revIndex != -1 {
g.revs = g.revs[revIndex:]
}
// remove any tombstone
if len(g.revs) == 1 && genIdx != len(ki.generations)-1 {
delete(available, g.revs[0])
genIdx++
}
}
// remove the previous generations.
ki.generations = ki.generations[genIdx:]
}
// keep finds the revision to be kept if compact is called at given atRev.
func (ki *keyIndex) keep(atRev int64, available map[revision]struct{}) {
if ki.isEmpty() {
return
}
genIdx, revIndex := ki.doCompact(atRev, available)
g := &ki.generations[genIdx]
if !g.isEmpty() {
// remove any tombstone
if revIndex == len(g.revs)-1 && genIdx != len(ki.generations)-1 {
delete(available, g.revs[revIndex])
}
}
}
func (ki *keyIndex) doCompact(atRev int64, available map[revision]struct{}) (genIdx int, revIndex int) {
// walk until reaching the first revision smaller or equal to "atRev",
// and add the revision to the available map
f := func(rev revision) bool {
if rev.main <= atRev {
available[rev] = struct{}{}
return false
}
return true
}
genIdx, g := 0, &ki.generations[0]
// find first generation includes atRev or created after atRev
for genIdx < len(ki.generations)-1 {
if tomb := g.revs[len(g.revs)-1].main; tomb > atRev {
break
}
genIdx++
g = &ki.generations[genIdx]
}
revIndex = g.walk(f)
return genIdx, revIndex
}
func (ki *keyIndex) isEmpty() bool {
return len(ki.generations) == 1 && ki.generations[0].isEmpty()
}
// findGeneration finds out the generation of the keyIndex that the
// given rev belongs to. If the given rev is at the gap of two generations,
// which means that the key does not exist at the given rev, it returns nil.
func (ki *keyIndex) findGeneration(rev int64) *generation {
lastg := len(ki.generations) - 1
cg := lastg
for cg >= 0 {
if len(ki.generations[cg].revs) == 0 {
cg--
continue
}
g := ki.generations[cg]
if cg != lastg {
if tomb := g.revs[len(g.revs)-1].main; tomb <= rev {
return nil
}
}
if g.revs[0].main <= rev {
return &ki.generations[cg]
}
cg--
}
return nil
}
func (a *keyIndex) Less(b btree.Item) bool {
return bytes.Compare(a.key, b.(*keyIndex).key) == -1
}
func (a *keyIndex) equal(b *keyIndex) bool {
if !bytes.Equal(a.key, b.key) {
return false
}
if a.modified != b.modified {
return false
}
if len(a.generations) != len(b.generations) {
return false
}
for i := range a.generations {
ag, bg := a.generations[i], b.generations[i]
if !ag.equal(bg) {
return false
}
}
return true
}
func (ki *keyIndex) String() string {
var s string
for _, g := range ki.generations {
s += g.String()
}
return s
}
// generation contains multiple revisions of a key.
type generation struct {
ver int64
created revision // when the generation is created (put in first revision).
revs []revision
}
func (g *generation) isEmpty() bool { return g == nil || len(g.revs) == 0 }
// walk walks through the revisions in the generation in descending order.
// It passes the revision to the given function.
// walk returns until: 1. it finishes walking all pairs 2. the function returns false.
// walk returns the position at where it stopped. If it stopped after
// finishing walking, -1 will be returned.
func (g *generation) walk(f func(rev revision) bool) int {
l := len(g.revs)
for i := range g.revs {
ok := f(g.revs[l-i-1])
if !ok {
return l - i - 1
}
}
return -1
}
func (g *generation) String() string {
return fmt.Sprintf("g: created[%d] ver[%d], revs %#v\n", g.created, g.ver, g.revs)
}
func (a generation) equal(b generation) bool {
if a.ver != b.ver {
return false
}
if len(a.revs) != len(b.revs) {
return false
}
for i := range a.revs {
ar, br := a.revs[i], b.revs[i]
if ar != br {
return false
}
}
return true
}
![swh spinner](/static/img/swh-spinner.gif)
Computing file changes ...