func (this *Paxos) doUpdateLearner(change *thispb.LearnerChange) error {
if this.chosenValue != nil {
return nil
}
if !this.wal.IsRecovering() {
walRecord := thispb.WALRecord{}
walRecord.LearnerChange = change
_, errQueue := wal.QueueChangeProto(this.wal, this.uid, &walRecord)
if errQueue != nil {
this.Errorf("could not write learner change record: %v", errQueue)
return errQueue
}
}
if change.ChosenValue != nil {
this.chosenValue = change.GetChosenValue()
this.Infof("consensus result learned from proposer is %s",
this.chosenValue)
if this.watch != nil {
this.watch.ConsensusUpdate(this.uid, -1, this.chosenValue)
}
return nil
}
acceptor := change.GetVotedAcceptor()
for index := range change.VotedBallotList {
ballot := change.VotedBallotList[index]
value := change.VotedValueList[index]
this.ballotValueMap[ballot] = value
acceptorSet, found := this.ballotAcceptorsMap[ballot]
if !found {
acceptorSet = make(map[string]struct{})
this.ballotAcceptorsMap[ballot] = acceptorSet
}
acceptorSet[acceptor] = struct{}{}
if len(acceptorSet) >= this.MajoritySize() {
this.chosenValue = value
this.Infof("consensus result learned through votes is %s", value)
if this.watch != nil {
this.watch.ConsensusUpdate(this.uid, -1, this.chosenValue)
}
}
}
return nil
}
// LearnRPC handles ClassicPaxos.Learn rpc.
func (this *Paxos) LearnRPC(header *msgpb.Header,
request *thispb.LearnRequest) (status error) {
if !this.IsLearner() {
this.Errorf("this paxos instance is not a learner; rejecting %s", header)
return errs.ErrInvalid
}
lock, errLock := this.ctlr.TimedLock(msg.RequestTimeout(header), "learner")
if errLock != nil {
return errLock
}
defer lock.Unlock()
acceptor := header.GetMessengerId()
if this.chosenValue == nil {
change := thispb.LearnerChange{}
change.VotedBallotList = request.VotedBallotList
change.VotedValueList = request.VotedValueList
change.VotedAcceptor = proto.String(acceptor)
if err := this.doUpdateLearner(&change); err != nil {
this.Errorf("could not update learner state: %v", err)
return err
}
}
response := thispb.LearnResponse{}
if this.chosenValue != nil {
response.KnowsChosenValue = proto.Bool(true)
}
message := thispb.PaxosMessage{}
message.LearnResponse = &response
errSend := msg.SendResponseProto(this.msn, header, &message)
if errSend != nil {
this.Errorf("could not respond to learn request from %s: %v", acceptor,
errSend)
return errSend
}
return nil
}
// ProposeRPC handles ClassicPaxos.Propose rpc.
func (this *Paxos) ProposeRPC(header *msgpb.Header,
request *thispb.ProposeRequest) (status error) {
if !this.IsProposer() {
this.Errorf("this paxos instance is not a proposer; rejecting %s", header)
return errs.ErrInvalid
}
// OPTIMIZATION If this object is also a learner and already knows the
// consensus result, we don't need to perform expensive proposal.
if this.IsLearner() {
lock := this.ctlr.ReadLock("learner")
defer lock.Unlock()
if this.chosenValue != nil {
response := thispb.ProposeResponse{}
response.ChosenValue = this.chosenValue
message := thispb.PaxosMessage{}
message.ProposeResponse = &response
errSend := msg.SendResponseProto(this.msn, header, &message)
if errSend != nil {
this.Errorf("could not send known chosen value as the propose "+
"response: %v", errSend)
return errSend
}
return nil
}
lock.Unlock()
}
var chosen []byte
proposal := request.GetProposedValue()
for ii := 0; chosen == nil && msg.RequestTimeout(header) > 0; ii++ {
if ii > 0 {
time.Sleep(this.opts.ProposeRetryInterval)
}
// Get the next proposal ballot number.
ballot, errNext := this.GetNextProposalBallot(msg.RequestTimeout(header))
if errNext != nil {
this.Errorf("could not select higher ballot: %v", errNext)
return errNext
}
this.Infof("using ballot number %d for the proposal", ballot)
lock := this.ctlr.ReadLock("config")
phase1AcceptorList := this.getPhase1AcceptorList(ballot)
lock.Unlock()
// Collect phase1 promises from majority number of acceptors.
votedValue, acceptorList, errPhase1 := this.doPhase1(header, ballot,
phase1AcceptorList)
if errPhase1 != nil {
this.Warningf("could not complete paxos phase1: %v", errPhase1)
continue
}
// If a value was already voted, it may have been chosen, so propose it
// instead.
value := proposal
if votedValue != nil {
value = votedValue
}
// Collect phase2 votes from majority number of acceptors.
errPhase2 := this.doPhase2(header, ballot, value, acceptorList)
if errPhase2 != nil {
this.Warningf("could not complete paxos phase2: %v", errPhase2)
continue
}
// A value is chosen, break out of the loop.
chosen = value
break
}
if chosen == nil {
this.Errorf("could not propose value %s", proposal)
return errs.ErrRetry
}
// If local node is a learner, update him with the consensus result directly.
defer func() {
if this.IsLearner() {
lock, errLock := this.ctlr.Lock("learner")
if errLock != nil {
return
}
defer lock.Unlock()
change := thispb.LearnerChange{}
change.ChosenValue = chosen
if err := this.doUpdateLearner(&change); err != nil {
this.Warningf("could not update local learner with the consensus "+
"result (ignored): %v", err)
}
}
}()
// Send propose response with chosen value.
response := thispb.ProposeResponse{}
response.ChosenValue = chosen
message := thispb.PaxosMessage{}
message.ProposeResponse = &response
errSend := msg.SendResponseProto(this.msn, header, &message)
if errSend != nil {
this.Errorf("could not send propose response: %v", errSend)
return errSend
}
return nil
}
