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leader.go
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leader.go
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// Copyright 2016 PingCAP, Inc.
//
// 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,
// See the License for the specific language governing permissions and
// limitations under the License.
package server
import (
"context"
"fmt"
"math/rand"
"path"
"strings"
"time"
"github.com/coreos/etcd/clientv3"
"github.com/coreos/etcd/mvcc/mvccpb"
"github.com/pingcap/kvproto/pkg/pdpb"
"github.com/pingcap/pd/pkg/etcdutil"
"github.com/pingcap/pd/pkg/logutil"
"github.com/pkg/errors"
log "github.com/sirupsen/logrus"
)
// IsLeader returns whether server is leader or not.
func (s *Server) IsLeader() bool {
// If server is not started. Both leaderID and ID could be 0.
return !s.isClosed() && s.GetLeaderID() == s.ID()
}
// GetLeaderID returns current leader's member ID.
func (s *Server) GetLeaderID() uint64 {
return s.GetLeader().GetMemberId()
}
// GetLeader returns current leader of pd cluster.
func (s *Server) GetLeader() *pdpb.Member {
leader := s.leader.Load()
if leader == nil {
return nil
}
member := leader.(*pdpb.Member)
if member.GetMemberId() == 0 {
return nil
}
return member
}
func (s *Server) enableLeader() {
s.leader.Store(s.member)
}
func (s *Server) disableLeader() {
s.leader.Store(&pdpb.Member{})
}
func (s *Server) getLeaderPath() string {
return path.Join(s.rootPath, "leader")
}
func (s *Server) leaderLoop() {
defer logutil.LogPanic()
defer s.serverLoopWg.Done()
for {
if s.isClosed() {
log.Infof("server is closed, return leader loop")
return
}
if s.GetEtcdLeader() == 0 {
log.Error("no etcd leader, check leader later")
time.Sleep(200 * time.Millisecond)
continue
}
leader, rev, err := getLeader(s.client, s.getLeaderPath())
if err != nil {
log.Errorf("get leader err %v", err)
time.Sleep(200 * time.Millisecond)
continue
}
if leader != nil {
if s.isSameLeader(leader) {
// oh, we are already leader, we may meet something wrong
// in previous campaignLeader. we can delete and campaign again.
log.Warnf("leader is still %s, delete and campaign again", leader)
if err = s.deleteLeaderKey(); err != nil {
log.Errorf("delete leader key err %s", err)
time.Sleep(200 * time.Millisecond)
continue
}
} else {
log.Infof("leader is %s, watch it", leader)
s.watchLeader(leader, rev)
log.Info("leader changed, try to campaign leader")
}
}
etcdLeader := s.GetEtcdLeader()
if etcdLeader != s.ID() {
log.Infof("%v is not etcd leader, skip campaign leader and check later", s.Name())
time.Sleep(200 * time.Millisecond)
continue
}
if err = s.campaignLeader(); err != nil {
log.Errorf("campaign leader err %s", fmt.Sprintf("%+v", err))
}
}
}
func (s *Server) etcdLeaderLoop() {
defer logutil.LogPanic()
defer s.serverLoopWg.Done()
ctx, cancel := context.WithCancel(s.serverLoopCtx)
defer cancel()
for {
select {
case <-time.After(s.cfg.leaderPriorityCheckInterval.Duration):
etcdLeader := s.GetEtcdLeader()
if etcdLeader == s.ID() || etcdLeader == 0 {
break
}
myPriority, err := s.GetMemberLeaderPriority(s.ID())
if err != nil {
log.Errorf("failed to load leader priority: %v", err)
break
}
leaderPriority, err := s.GetMemberLeaderPriority(etcdLeader)
if err != nil {
log.Errorf("failed to load leader priority: %v", err)
break
}
if myPriority > leaderPriority {
err := s.etcd.Server.MoveLeader(ctx, etcdLeader, s.ID())
if err != nil {
log.Errorf("failed to transfer etcd leader: %v", err)
} else {
log.Infof("etcd leader moved from %v to %v", etcdLeader, s.ID())
}
}
case <-ctx.Done():
log.Info("server is closed, exit etcd leader loop")
return
}
}
}
// getLeader gets server leader from etcd.
func getLeader(c *clientv3.Client, leaderPath string) (*pdpb.Member, int64, error) {
leader := &pdpb.Member{}
ok, rev, err := getProtoMsgWithModRev(c, leaderPath, leader)
if err != nil {
return nil, 0, err
}
if !ok {
return nil, 0, nil
}
return leader, rev, nil
}
// GetEtcdLeader returns the etcd leader ID.
func (s *Server) GetEtcdLeader() uint64 {
return s.etcd.Server.Lead()
}
func (s *Server) isSameLeader(leader *pdpb.Member) bool {
return leader.GetMemberId() == s.ID()
}
func (s *Server) memberInfo() (member *pdpb.Member, marshalStr string) {
leader := &pdpb.Member{
Name: s.Name(),
MemberId: s.ID(),
ClientUrls: strings.Split(s.cfg.AdvertiseClientUrls, ","),
PeerUrls: strings.Split(s.cfg.AdvertisePeerUrls, ","),
}
data, err := leader.Marshal()
if err != nil {
// can't fail, so panic here.
log.Fatalf("marshal leader %s err %v", leader, err)
}
return leader, string(data)
}
func (s *Server) campaignLeader() error {
log.Infof("start to campaign leader %s", s.Name())
lessor := clientv3.NewLease(s.client)
defer func() {
lessor.Close()
log.Info("exit campaign leader")
}()
start := time.Now()
ctx, cancel := context.WithTimeout(s.client.Ctx(), requestTimeout)
leaseResp, err := lessor.Grant(ctx, s.cfg.LeaderLease)
cancel()
if cost := time.Since(start); cost > slowRequestTime {
log.Warnf("lessor grants too slow, cost %s", cost)
}
if err != nil {
return errors.WithStack(err)
}
leaderKey := s.getLeaderPath()
// The leader key must not exist, so the CreateRevision is 0.
resp, err := s.txn().
If(clientv3.Compare(clientv3.CreateRevision(leaderKey), "=", 0)).
Then(clientv3.OpPut(leaderKey, s.memberValue, clientv3.WithLease(leaseResp.ID))).
Commit()
if err != nil {
return errors.WithStack(err)
}
if !resp.Succeeded {
return errors.New("failed to campaign leader, other server may campaign ok")
}
// Make the leader keepalived.
ctx, cancel = context.WithCancel(s.serverLoopCtx)
defer cancel()
ch, err := lessor.KeepAlive(ctx, leaseResp.ID)
if err != nil {
return errors.WithStack(err)
}
log.Infof("campaign leader ok %s", s.Name())
err = s.scheduleOpt.reload(s.kv)
if err != nil {
return err
}
// Try to create raft cluster.
err = s.createRaftCluster()
if err != nil {
return err
}
defer s.stopRaftCluster()
log.Debug("sync timestamp for tso")
if err = s.syncTimestamp(); err != nil {
return err
}
defer s.ts.Store(&atomicObject{
physical: zeroTime,
})
s.enableLeader()
defer s.disableLeader()
log.Infof("cluster version is %s", s.scheduleOpt.loadClusterVersion())
log.Infof("PD cluster leader %s is ready to serve", s.Name())
CheckPDVersion(s.scheduleOpt)
tsTicker := time.NewTicker(updateTimestampStep)
defer tsTicker.Stop()
for {
select {
case _, ok := <-ch:
if !ok {
log.Info("keep alive channel is closed")
return nil
}
case <-tsTicker.C:
if err = s.updateTimestamp(); err != nil {
log.Info("failed to update timestamp")
return err
}
etcdLeader := s.GetEtcdLeader()
if etcdLeader != s.ID() {
log.Infof("etcd leader changed, %s resigns leadership", s.Name())
return nil
}
case <-ctx.Done():
return errors.New("server closed")
}
}
}
func (s *Server) watchLeader(leader *pdpb.Member, revision int64) {
s.leader.Store(leader)
defer s.leader.Store(&pdpb.Member{})
watcher := clientv3.NewWatcher(s.client)
defer watcher.Close()
ctx, cancel := context.WithCancel(s.serverLoopCtx)
defer cancel()
// The revision is the revision of last modification on this key.
// If the revision is compacted, will meet required revision has been compacted error.
// In this case, use the compact revision to re-watch the key.
for {
// gofail: var delayWatcher struct{}
rch := watcher.Watch(ctx, s.getLeaderPath(), clientv3.WithRev(revision))
for wresp := range rch {
// meet compacted error, use the compact revision.
if wresp.CompactRevision != 0 {
log.Warnf("required revision %d has been compacted, use the compact revision %d", revision, wresp.CompactRevision)
revision = wresp.CompactRevision
break
}
if wresp.Canceled {
log.Errorf("leader watcher is canceled with revision: %d, error: %s", revision, wresp.Err())
return
}
for _, ev := range wresp.Events {
if ev.Type == mvccpb.DELETE {
log.Info("leader is deleted")
return
}
}
}
select {
case <-ctx.Done():
// server closed, return
return
default:
}
}
}
// ResignLeader resigns current PD's leadership. If nextLeader is empty, all
// other pd-servers can campaign.
func (s *Server) ResignLeader(nextLeader string) error {
log.Infof("%s tries to resign leader with next leader directive: %v", s.Name(), nextLeader)
// Determine next leaders.
var leaderIDs []uint64
res, err := etcdutil.ListEtcdMembers(s.client)
if err != nil {
return err
}
for _, member := range res.Members {
if (nextLeader == "" && member.ID != s.id) || (nextLeader != "" && member.Name == nextLeader) {
leaderIDs = append(leaderIDs, member.GetID())
}
}
if len(leaderIDs) == 0 {
return errors.New("no valid pd to transfer leader")
}
nextLeaderID := leaderIDs[rand.Intn(len(leaderIDs))]
log.Infof("%s ready to resign leader, next leader: %v", s.Name(), nextLeaderID)
err = s.etcd.Server.MoveLeader(s.serverLoopCtx, s.ID(), nextLeaderID)
return errors.WithStack(err)
}
func (s *Server) deleteLeaderKey() error {
// delete leader itself and let others start a new election again.
leaderKey := s.getLeaderPath()
resp, err := s.leaderTxn().Then(clientv3.OpDelete(leaderKey)).Commit()
if err != nil {
return errors.WithStack(err)
}
if !resp.Succeeded {
return errors.New("resign leader failed, we are not leader already")
}
return nil
}
func (s *Server) leaderCmp() clientv3.Cmp {
return clientv3.Compare(clientv3.Value(s.getLeaderPath()), "=", s.memberValue)
}