forked from tikv/pd
/
leader.go
368 lines (319 loc) · 8.91 KB
/
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"
"path"
"strconv"
"strings"
"sync/atomic"
"time"
log "github.com/Sirupsen/logrus"
"github.com/coreos/etcd/clientv3"
"github.com/coreos/etcd/mvcc/mvccpb"
"github.com/juju/errors"
"github.com/pingcap/kvproto/pkg/pdpb"
"github.com/pingcap/pd/pkg/etcdutil"
)
var (
errNoLeader = errors.New("no leader")
resignLeaderTimeout = time.Second * 5
nextLeaderTTL = 10 // in seconds
)
// IsLeader returns whether server is leader or not.
func (s *Server) IsLeader() bool {
return atomic.LoadInt64(&s.isLeader) == 1
}
func (s *Server) enableLeader(b bool) {
value := int64(0)
if b {
value = 1
}
atomic.StoreInt64(&s.isLeader, value)
}
func (s *Server) getLeaderPath() string {
return path.Join(s.rootPath, "leader")
}
func (s *Server) getNextLeaderPath() string {
return path.Join(s.rootPath, "next_leader")
}
func (s *Server) leaderLoop() {
defer s.wg.Done()
for {
if s.isClosed() {
log.Infof("server is closed, return leader loop")
return
}
leader, 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()
log.Info("leader changed, try to campaign leader")
}
}
// Check if current pd is expected to be next leader.
nextLeaders, err := getNextLeaders(s.client, s.getNextLeaderPath())
if err != nil {
log.Errorf("check next leader failed: %v", err)
time.Sleep(200 * time.Millisecond)
continue
}
if len(nextLeaders) > 0 {
if _, ok := nextLeaders[s.id]; !ok {
time.Sleep(200 * time.Millisecond)
continue
}
}
if err = s.campaignLeader(); err != nil {
log.Errorf("campaign leader err %s", errors.ErrorStack(err))
}
}
}
func getLeaderAddr(leader *pdpb.Member) string {
return strings.Join(leader.GetClientUrls(), ",")
}
// getLeader gets server leader from etcd.
func getLeader(c *clientv3.Client, leaderPath string) (*pdpb.Member, error) {
leader := &pdpb.Member{}
ok, err := getProtoMsg(c, leaderPath, leader)
if err != nil {
return nil, errors.Trace(err)
}
if !ok {
return nil, nil
}
return leader, nil
}
func getNextLeaders(c *clientv3.Client, path string) (map[uint64]struct{}, error) {
val, err := getValue(c, path)
if err != nil {
return nil, errors.Trace(err)
}
if len(val) == 0 {
return nil, nil
}
ids := make(map[uint64]struct{})
for _, idStr := range strings.Split(string(val), ",") {
id, err := strconv.ParseUint(idStr, 10, 64)
if err != nil {
return nil, errors.Trace(err)
}
ids[id] = struct{}{}
}
return ids, nil
}
// GetLeader gets pd cluster leader.
func (s *Server) GetLeader() (*pdpb.Member, error) {
if s.isClosed() {
return nil, errors.New("server is closed")
}
leader, err := getLeader(s.client, s.getLeaderPath())
if err != nil {
return nil, errors.Trace(err)
}
if leader == nil {
return nil, errors.Trace(errNoLeader)
}
return leader, nil
}
func (s *Server) isSameLeader(leader *pdpb.Member) bool {
return leader.GetMemberId() == s.ID()
}
func (s *Server) marshalLeader() 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 string(data)
}
func (s *Server) campaignLeader() error {
log.Debugf("begin to campaign leader %s", s.Name())
lessor := clientv3.NewLease(s.client)
defer lessor.Close()
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.Trace(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.leaderValue, clientv3.WithLease(clientv3.LeaseID(leaseResp.ID)))).
Commit()
if err != nil {
return errors.Trace(err)
}
if !resp.Succeeded {
return errors.New("campaign leader failed, other server may campaign ok")
}
// Make the leader keepalived.
ctx, cancel = context.WithCancel(s.client.Ctx())
defer cancel()
ch, err := lessor.KeepAlive(ctx, clientv3.LeaseID(leaseResp.ID))
if err != nil {
return errors.Trace(err)
}
log.Debugf("campaign leader ok %s", s.Name())
err = s.scheduleOpt.reload(s.kv)
if err != nil {
return errors.Trace(err)
}
// Try to create raft cluster.
err = s.createRaftCluster()
if err != nil {
return errors.Trace(err)
}
defer s.stopRaftCluster()
log.Debug("sync timestamp for tso")
if err = s.syncTimestamp(); err != nil {
return errors.Trace(err)
}
defer s.ts.Store(&atomicObject{
physical: zeroTime,
})
s.enableLeader(true)
defer s.enableLeader(false)
log.Infof("PD cluster leader %s is ready to serve", s.Name())
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 {
return errors.Trace(err)
}
case <-s.resignCh:
log.Infof("%s resigns leadership", s.Name())
return nil
case <-ctx.Done():
return errors.New("server closed")
}
}
}
func (s *Server) watchLeader() {
watcher := clientv3.NewWatcher(s.client)
defer watcher.Close()
ctx, cancel := context.WithCancel(s.client.Ctx())
defer cancel()
for {
rch := watcher.Watch(ctx, s.getLeaderPath())
for wresp := range rch {
if wresp.Canceled {
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 []string
res, err := etcdutil.ListEtcdMembers(s.client)
if err != nil {
return errors.Trace(err)
}
for _, member := range res.Members {
if (nextLeader == "" && member.ID != s.id) || (nextLeader != "" && member.Name == nextLeader) {
leaderIDs = append(leaderIDs, strconv.FormatUint(member.ID, 10))
}
}
nextLeaderValue := strings.Join(leaderIDs, ",")
// Save expect leader(s) to etcd.
lease := clientv3.NewLease(s.client)
defer lease.Close()
ctx, cancel := context.WithTimeout(s.client.Ctx(), requestTimeout)
leaseRes, err := lease.Grant(ctx, int64(nextLeaderTTL))
cancel()
if err != nil {
return errors.Trace(err)
}
resp, err := s.leaderTxn().
Then(clientv3.OpPut(s.getNextLeaderPath(), nextLeaderValue, clientv3.WithLease(clientv3.LeaseID(leaseRes.ID)))).
Commit()
if err != nil {
return errors.Trace(err)
}
if !resp.Succeeded {
return errors.New("save next leader failed, maybe lost leadership")
}
log.Infof("%s ready to resign leader, expect next leaders: %v", s.Name(), nextLeaderValue)
// Resign leader.
select {
case s.resignCh <- struct{}{}:
return nil
case <-time.After(resignLeaderTimeout):
return errors.Errorf("failed to send resign signal, maybe not leader")
}
}
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.Trace(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.leaderValue)
}