golang源码分析：etcd（19）

golangLeetcode

发布于 2023-09-20 08:30:46

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etcd的增删改都会增加全局版本号，删除也是软删除，虽然便于回溯修改历史，但是随之带来问题，数据量的膨胀。因此需要进行压缩，也就是compact。假如我们制定压缩版本是v6，那么v6之前的所有已经删除的key会被删除，没有被删除的key保留最新的版本，丢弃之前的修改历史。

etcd有三种compact策略：1，用户手动执行compact命令；2，定期执行compact，删除掉比较久远的老版本3，根据版本压缩，删除某个版本以前的版本。下面我们通过源码分析下整个compact执行的流程。

server/etcdserver/server.go etcd server在启动的时候会根据配置参数启动compactor，然后周期性执行run方法

 func NewServer(cfg config.ServerConfig) (srv *EtcdServer, err error) {
    if num := cfg.AutoCompactionRetention; num != 0 {
    srv.compactor, err = v3compactor.New(cfg.Logger, cfg.AutoCompactionMode, num, srv.kv, srv)
    if err != nil {
      return nil, err
    }
    srv.compactor.Run()
  }

server/etcdserver/api/v3compactor/compactor.go里根据参数启动不同的compactor

func New(
  lg *zap.Logger,
  mode string,
  retention time.Duration,
  rg RevGetter,
  c Compactable,
) (Compactor, error) {
        switch mode {
  case ModePeriodic:
    return newPeriodic(lg, clockwork.NewRealClock(), retention, rg, c), nil
  case ModeRevision:
    return newRevision(lg, clockwork.NewRealClock(), int64(retention), rg, c), nil

type Compactable interface {
  Compact(ctx context.Context, r *pb.CompactionRequest) (*pb.CompactionResponse, error)
}

server/etcdserver/api/v3compactor/periodic.go具体实现如下

func newPeriodic(lg *zap.Logger, clock clockwork.Clock, h time.Duration, rg RevGetter, c Compactable) *Periodic {

type Periodic struct {
  lg     *zap.Logger
  clock  clockwork.Clock
  period time.Duration


  rg RevGetter
  c  Compactable


  revs   []int64
  ctx    context.Context
  cancel context.CancelFunc


  // mu protects paused
  mu     sync.RWMutex
  paused bool
}

调用srv的Compact方法

func (pc *Periodic) Run() {
        go func() {
            for {
      pc.revs = append(pc.revs, pc.rg.Rev())
          _, err := pc.c.Compact(pc.ctx, &pb.CompactionRequest{Revision: rev})

server/etcdserver/api/v3compactor/revision.go

func newRevision(lg *zap.Logger, clock clockwork.Clock, retention int64, rg RevGetter, c Compactable) *Revision {

type Revision struct {
  lg *zap.Logger


  clock     clockwork.Clock
  retention int64


  rg RevGetter
  c  Compactable


  ctx    context.Context
  cancel context.CancelFunc


  mu     sync.Mutex
  paused bool
}

func (rc *Revision) Run() {
   go func() {
    for {
          _, err := rc.c.Compact(rc.ctx, &pb.CompactionRequest{Revision: rev})

最后一个参数srv调用的是server的Compact函数，向集群提交raft请求，然后等待Physc里返回结果

server/etcdserver/v3_server.go

func (s *EtcdServer) Compact(ctx context.Context, r *pb.CompactionRequest) (*pb.CompactionResponse, error) {
      result, err := s.processInternalRaftRequestOnce(ctx, pb.InternalRaftRequest{Compaction: r})
        <-result.Physc

func (s *EtcdServer) processInternalRaftRequestOnce(ctx context.Context, r pb.InternalRaftRequest) (*apply2.Result, error) {
      err = s.r.Propose(cctx, data)
      return nil, s.parseProposeCtxErr(cctx.Err(), start)

server在后台启动了一个协程，等处理完成后把结果放入Physc里面

func (s *EtcdServer) Start() {
      s.start()

func (s *EtcdServer) start() {
      go s.run()

里面调用了ApplayAll方法

func (s *EtcdServer) run() {
   for {
    select {
    case ap := <-s.r.apply():
      f := schedule.NewJob("server_applyAll", func(context.Context) { s.applyAll(&ep, &ap) })
      sched.Schedule(f)

func (s *EtcdServer) applyAll(ep *etcdProgress, apply *toApply) {
      s.applyEntries(ep, apply)

func (s *EtcdServer) applyEntries(ep *etcdProgress, apply *toApply) {
        if ep.appliedt, ep.appliedi, shouldstop = s.apply(ents, &ep.confState); shouldstop {

func (s *EtcdServer) apply(
  es []raftpb.Entry,
  confState *raftpb.ConfState,
) (appliedt uint64, appliedi uint64, shouldStop bool) {
 switch e.Type {
    case raftpb.EntryNormal:
      s.applyEntryNormal(&e)
      s.setAppliedIndex(e.Index)
      s.setTerm(e.Term)

func (s *EtcdServer) applyEntryNormal(e *raftpb.Entry) {
    if needResult || !noSideEffect(&raftReq) {
    if !needResult && raftReq.Txn != nil {
      removeNeedlessRangeReqs(raftReq.Txn)
    }
    ar = s.uberApply.Apply(&raftReq, shouldApplyV3)

server/etcdserver/apply/uber_applier.go

func (a *uberApplier) Apply(r *pb.InternalRaftRequest, shouldApplyV3 membership.ShouldApplyV3) *Result {
      return a.applyV3.Apply(context.TODO(), r, shouldApplyV3, a.dispatch)

在Apply里面会根据消息类型来进行分发处理

func (a *uberApplier) dispatch(ctx context.Context, r *pb.InternalRaftRequest, shouldApplyV3 membership.ShouldApplyV3) *Result {
    case r.Compaction != nil:
    op = "Compaction"
    ar.Resp, ar.Physc, ar.Trace, ar.Err = a.applyV3.Compaction(r.Compaction)

server/etcdserver/apply/apply.go最终调用kv的Compact方法来进行压缩操作，至此完成了前端部分的流程

func (a *applierV3backend) Compaction(compaction *pb.CompactionRequest) (*pb.CompactionResponse, <-chan struct{}, *traceutil.Trace, error) {
      ch, err := a.kv.Compact(trace, compaction.Revision)

接着我们看下后端操作 server/storage/mvcc/kv.go

type KV interface {
      Compact(trace *traceutil.Trace, rev int64) (<-chan struct{}, error)

server/storage/mvcc/kvstore.go

    func (s *store) Compact(trace *traceutil.Trace, rev int64) (<-chan struct{}, error) {
      return s.compact(trace, rev, prevCompactRev)

func (s *store) compact(trace *traceutil.Trace, rev, prevCompactRev int64) (<-chan struct{}, error) {
  j := schedule.NewJob("kvstore_compact", func(ctx context.Context) {
  if ctx.Err() != nil {
  s.compactBarrier(ctx, ch)
  return
  }
  hash, err := s.scheduleCompaction(rev, prevCompactRev)
  s.fifoSched.Schedule(j)

server/storage/mvcc/kvstore_compaction.go里面是核心的处理流程，先从btree上删除需要压缩的revision，然后使用tx的UndafeDelete方法，将revision从bolt里删除。

func (s *store) scheduleCompaction(compactMainRev, prevCompactRev int64) (KeyValueHash, error) {
  keep := s.kvindex.Compact(compactMainRev)
  for {
    keys, values := tx.UnsafeRange(schema.Key, last, end, int64(batchNum))
     for i := range keys {
      rev = bytesToRev(keys[i])
      if _, ok := keep[rev]; !ok {
        tx.UnsafeDelete(schema.Key, keys[i])

server/storage/mvcc/index.go keyIndex里的删除流程如下，先计算需要删除的revision，然后调用Delete方法从btree删除

func (ti *treeIndex) Compact(rev int64) map[revision]struct{} {
      keyi.compact(ti.lg, rev, available)
     if keyi.isEmpty() {
      _, ok := ti.tree.Delete(keyi)

server/storage/mvcc/key_index.go里计算方法如下：

func (ki *keyIndex) compact(lg *zap.Logger, atRev int64, available map[revision]struct{}) {
      genIdx, revIndex := ki.doCompact(atRev, available)

func (ki *keyIndex) doCompact(atRev int64, available map[revision]struct{}) (genIdx int, revIndex int) {
   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)

整体链路还是相对复杂的，通过channel来同步压缩结果，通过raft协议来保证节点之间的一致性。

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原始发表：2023-09-17 00:00，如有侵权请联系 cloudcommunity@tencent.com 删除

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