// checkAndRecoverDeadCoMaster checks a given analysis, decides whether to take action, and possibly takes action
// Returns true when action was taken.
func checkAndRecoverDeadCoMaster(analysisEntry inst.ReplicationAnalysis, candidateInstanceKey *inst.InstanceKey, forceInstanceRecovery bool, skipProcesses bool) (bool, *TopologyRecovery, error) {
	failedInstanceKey := &analysisEntry.AnalyzedInstanceKey
	if !(forceInstanceRecovery || analysisEntry.ClusterDetails.HasAutomatedMasterRecovery) {
		return false, nil, nil
	}
	topologyRecovery, err := AttemptRecoveryRegistration(&analysisEntry, !forceInstanceRecovery, !forceInstanceRecovery)
	if topologyRecovery == nil {
		log.Debugf("topology_recovery: found an active or recent recovery on %+v. Will not issue another RecoverDeadCoMaster.", analysisEntry.AnalyzedInstanceKey)
		return false, nil, err
	}

	// That's it! We must do recovery!
	recoverDeadCoMasterCounter.Inc(1)
	coMaster, lostSlaves, err := RecoverDeadCoMaster(topologyRecovery, skipProcesses)
	ResolveRecovery(topologyRecovery, coMaster)
	if coMaster == nil {
		inst.AuditOperation("recover-dead-co-master", failedInstanceKey, "Failure: no slave promoted.")
	} else {
		inst.AuditOperation("recover-dead-co-master", failedInstanceKey, fmt.Sprintf("promoted co-master: %+v", coMaster.Key))
	}
	topologyRecovery.LostSlaves.AddInstances(lostSlaves)
	if coMaster != nil {
		// success
		recoverDeadCoMasterSuccessCounter.Inc(1)

		if !skipProcesses {
			// Execute post intermediate-master-failover processes
			topologyRecovery.SuccessorKey = &coMaster.Key
			executeProcesses(config.Config.PostMasterFailoverProcesses, "PostMasterFailoverProcesses", topologyRecovery, false)
		}
	} else {
		recoverDeadCoMasterFailureCounter.Inc(1)
	}
	return true, topologyRecovery, err
}

func RecoverDeadIntermediateMaster(analysisEntry inst.ReplicationAnalysis) (actionTaken bool, successorInstance *inst.Instance, err error) {
	failedInstanceKey := &analysisEntry.AnalyzedInstanceKey
	if ok, err := AttemptRecoveryRegistration(&analysisEntry); !ok {
		log.Debugf("topology_recovery: found an active or recent recovery on %+v. Will not issue another RecoverDeadIntermediateMaster.", *failedInstanceKey)
		return false, nil, err
	}

	inst.AuditOperation("recover-dead-intermediate-master", failedInstanceKey, "problem found; will recover")
	log.Debugf("topology_recovery: RecoverDeadIntermediateMaster: will recover %+v", *failedInstanceKey)
	if err := executeProcesses(config.Config.PreFailoverProcesses, "PreFailoverProcesses", analysisEntry, nil, true); err != nil {
		return false, nil, err
	}

	// Plan A: find a replacement intermediate master
	if candidateSibling, err := GetCandidateSiblingOfIntermediateMaster(failedInstanceKey); err == nil {
		log.Debugf("topology_recovery: - RecoverDeadIntermediateMaster: will attempt a candidate intermediate master: %+v", candidateSibling.Key)
		// We have a candidate
		if matchedSlaves, candidateSibling, err, errs := inst.MultiMatchSlaves(failedInstanceKey, &candidateSibling.Key, ""); err == nil {
			ResolveRecovery(failedInstanceKey, &candidateSibling.Key)

			successorInstance = candidateSibling
			actionTaken = true

			log.Debugf("topology_recovery: - RecoverDeadIntermediateMaster: move to candidate intermediate master (%+v) went with %d errors", candidateSibling.Key, len(errs))
			inst.AuditOperation("recover-dead-intermediate-master", failedInstanceKey, fmt.Sprintf("Done. Matched %d slaves under candidate sibling: %+v; %d errors: %+v", len(matchedSlaves), candidateSibling.Key, len(errs), errs))
		} else {
			log.Debugf("topology_recovery: - RecoverDeadIntermediateMaster: move to candidate intermediate master (%+v) did not complete: %+v", candidateSibling.Key, err)
			inst.AuditOperation("recover-dead-intermediate-master", failedInstanceKey, fmt.Sprintf("Matched %d slaves under candidate sibling: %+v; %d errors: %+v", len(matchedSlaves), candidateSibling.Key, len(errs), errs))
		}
	}
	if !actionTaken {
		// Either no candidate or only partial match of slaves. Regroup as plan B
		inst.RegroupSlaves(failedInstanceKey, nil)
		// We don't care much if regroup made it or not. We prefer that it made it, in whcih case we only need to match up
		// one slave, but the operation is still valid if regroup partially/completely failed. We just promote anything
		// not regrouped.
		// So, match up all that's left, plan C
		log.Debugf("topology_recovery: - RecoverDeadIntermediateMaster: will next attempt a match up from %+v", *failedInstanceKey)

		var errs []error
		var matchedSlaves [](*inst.Instance)
		matchedSlaves, successorInstance, err, errs = inst.MatchUpSlaves(failedInstanceKey, "")
		if len(matchedSlaves) == 0 {
			log.Errorf("topology_recovery: RecoverDeadIntermediateMaster failed to match up any slave from %+v", *failedInstanceKey)
			return false, successorInstance, err
		}
		ResolveRecovery(failedInstanceKey, &successorInstance.Key)
		actionTaken = true

		log.Debugf("topology_recovery: - RecoverDeadIntermediateMaster: matched up to %+v", successorInstance.Key)
		inst.AuditOperation("recover-dead-intermediate-master", failedInstanceKey, fmt.Sprintf("Done. Matched slaves under: %+v %d errors: %+v", successorInstance.Key, len(errs), errs))
	}
	return actionTaken, successorInstance, err
}

// AuditAgentOperation creates and writes a new audit entry by given agent
func auditAgentOperation(auditType string, agent *Agent, message string) error {

	instanceKey := &inst.InstanceKey{}
	if agent != nil {
		instanceKey = &inst.InstanceKey{Hostname: agent.Hostname, Port: int(agent.MySQLPort)}
	}
	return inst.AuditOperation(auditType, instanceKey, message)
}

// Force a re-read of a topology instance; this is done because we need to substantiate a suspicion that we may have a failover
// scenario. we want to speed up rading the complete picture.
func emergentlyReadTopologyInstance(instanceKey *inst.InstanceKey, analysisCode inst.AnalysisCode) {
	if err := emergencyReadTopologyInstanceMap.Add(instanceKey.DisplayString(), true, 0); err == nil {
		emergencyReadTopologyInstanceMap.Set(instanceKey.DisplayString(), true, 0)
		go inst.ExecuteOnTopology(func() {
			inst.ReadTopologyInstance(instanceKey)
			inst.AuditOperation("emergently-read-topology-instance", instanceKey, string(analysisCode))
		})
	}
}

// Force a re-read of a topology instance; this is done because we need to substantiate a suspicion that we may have a failover
// scenario. we want to speed up reading the complete picture.
func emergentlyReadTopologyInstance(instanceKey *inst.InstanceKey, analysisCode inst.AnalysisCode) {
	if existsInCacheError := emergencyReadTopologyInstanceMap.Add(instanceKey.DisplayString(), true, cache.DefaultExpiration); existsInCacheError != nil {
		// Just recently attempted
		return
	}
	go inst.ExecuteOnTopology(func() {
		inst.ReadTopologyInstance(instanceKey)
		inst.AuditOperation("emergently-read-topology-instance", instanceKey, string(analysisCode))
	})
}

func RecoverDeadMaster(analysisEntry inst.ReplicationAnalysis) (bool, *inst.Instance, error) {
	failedInstanceKey := &analysisEntry.AnalyzedInstanceKey
	if ok, err := AttemptRecoveryRegistration(&analysisEntry); !ok {
		log.Debugf("topology_recovery: found an active or recent recovery on %+v. Will not issue another RecoverDeadMaster.", *failedInstanceKey)
		return false, nil, err
	}

	inst.AuditOperation("recover-dead-master", failedInstanceKey, "problem found; will recover")
	if err := executeProcesses(config.Config.PreFailoverProcesses, "PreFailoverProcesses", analysisEntry, nil, true); err != nil {
		return false, nil, err
	}

	log.Debugf("topology_recovery: RecoverDeadMaster: will recover %+v", *failedInstanceKey)
	_, _, _, candidateSlave, err := inst.RegroupSlaves(failedInstanceKey, nil)

	ResolveRecovery(failedInstanceKey, &candidateSlave.Key)

	log.Debugf("topology_recovery: - RecoverDeadMaster: candidate slave is %+v", candidateSlave.Key)
	inst.AuditOperation("recover-dead-master", failedInstanceKey, fmt.Sprintf("master: %+v", candidateSlave.Key))

	return true, candidateSlave, err
}

// acceptSignals registers for OS signals
func acceptSignals() {
	c := make(chan os.Signal, 1)

	signal.Notify(c, syscall.SIGHUP)
	go func() {
		for sig := range c {
			switch sig {
			case syscall.SIGHUP:
				log.Debugf("Received SIGHUP. Reloading configuration")
				config.Reload()
				inst.AuditOperation("reload-configuration", nil, "Triggered via SIGHUP")
			}
		}
	}()
}

// Start discovery begins a one time asynchronuous discovery process for the given
// instance and all of its topology connected instances.
// That is, the instance will be investigated for master and slaves, and the routines will follow on
// each and every such found master/slave.
// In essense, assuming all slaves in a replication topology are running, and given a single instance
// in such topology, this function will detect the entire topology.
func StartDiscovery(instanceKey inst.InstanceKey) {
	log.Infof("Starting discovery at %+v", instanceKey)
	pendingTokens := make(chan bool, maxConcurrency)
	completedTokens := make(chan bool, maxConcurrency)

	accountedDiscoverInstance(instanceKey, pendingTokens, completedTokens)
	go handleDiscoveryRequests(pendingTokens, completedTokens)

	// Block until all are complete
	for {
		select {
		case <-pendingTokens:
			<-completedTokens
		default:
			inst.AuditOperation("start-discovery", &instanceKey, "")
			return
		}
	}
}

func RecoverDeadIntermediateMaster(analysisEntry inst.ReplicationAnalysis, skipProcesses bool) (actionTaken bool, successorInstance *inst.Instance, err error) {
	failedInstanceKey := &analysisEntry.AnalyzedInstanceKey
	if ok, err := AttemptRecoveryRegistration(&analysisEntry); !ok {
		log.Debugf("topology_recovery: found an active or recent recovery on %+v. Will not issue another RecoverDeadIntermediateMaster.", *failedInstanceKey)
		return false, nil, err
	}

	inst.AuditOperation("recover-dead-intermediate-master", failedInstanceKey, "problem found; will recover")
	log.Debugf("topology_recovery: RecoverDeadIntermediateMaster: will recover %+v", *failedInstanceKey)
	if !skipProcesses {
		if err := executeProcesses(config.Config.PreFailoverProcesses, "PreFailoverProcesses", analysisEntry, nil, emptySlavesList, true); err != nil {
			return false, nil, err
		}
	}

	intermediateMasterInstance, _, err := inst.ReadInstance(failedInstanceKey)
	if err != nil {
		return false, nil, err
	}
	// Plan A: find a replacement intermediate master in same Data Center
	candidateSiblingOfIntermediateMaster, err := GetCandidateSiblingOfIntermediateMaster(intermediateMasterInstance)

	relocateSlavesToCandidateSibling := func() {
		if candidateSiblingOfIntermediateMaster == nil {
			return
		}
		log.Debugf("topology_recovery: - RecoverDeadIntermediateMaster: will attempt a candidate intermediate master: %+v", candidateSiblingOfIntermediateMaster.Key)
		// We have a candidate
		if relocatedSlaves, candidateSibling, err, errs := inst.RelocateSlaves(failedInstanceKey, &candidateSiblingOfIntermediateMaster.Key, ""); err == nil {
			ResolveRecovery(failedInstanceKey, &candidateSibling.Key)

			successorInstance = candidateSibling
			actionTaken = true

			log.Debugf("topology_recovery: - RecoverDeadIntermediateMaster: move to candidate intermediate master (%+v) went with %d errors", candidateSibling.Key, len(errs))
			inst.AuditOperation("recover-dead-intermediate-master", failedInstanceKey, fmt.Sprintf("Done. Relocated %d slaves under candidate sibling: %+v; %d errors: %+v", len(relocatedSlaves), candidateSibling.Key, len(errs), errs))
		} else {
			log.Debugf("topology_recovery: - RecoverDeadIntermediateMaster: move to candidate intermediate master (%+v) did not complete: %+v", candidateSibling.Key, err)
			inst.AuditOperation("recover-dead-intermediate-master", failedInstanceKey, fmt.Sprintf("Relocated %d slaves under candidate sibling: %+v; %d errors: %+v", len(relocatedSlaves), candidateSibling.Key, len(errs), errs))
		}
	}
	if candidateSiblingOfIntermediateMaster != nil && candidateSiblingOfIntermediateMaster.DataCenter == intermediateMasterInstance.DataCenter {
		relocateSlavesToCandidateSibling()
	}
	if !actionTaken {
		log.Debugf("topology_recovery: - RecoverDeadIntermediateMaster: will next attempt regrouping of slaves")
		// Plan B: regroup (we wish to reduce cross-DC replication streams)
		_, _, _, _, err = inst.RegroupSlaves(failedInstanceKey, true, nil)
		if err != nil {
			log.Debugf("topology_recovery: - RecoverDeadIntermediateMaster: regroup failed on: %+v", err)
		}
		// Plan C: try replacement intermediate master in other DC...
		if candidateSiblingOfIntermediateMaster != nil && candidateSiblingOfIntermediateMaster.DataCenter != intermediateMasterInstance.DataCenter {
			log.Debugf("topology_recovery: - RecoverDeadIntermediateMaster: will next attempt relocating to another DC server")
			relocateSlavesToCandidateSibling()
		}
	}
	if !actionTaken {
		// Do we still have leftovers? Some slaves couldn't move? Couldn't regroup? Only left with regroup's resulting leader?
		// nothing moved?
		// We don't care much if regroup made it or not. We prefer that it made it, in whcih case we only need to relocate up
		// one slave, but the operation is still valid if regroup partially/completely failed. We just promote anything
		// not regrouped.
		// So, match up all that's left, plan D
		log.Debugf("topology_recovery: - RecoverDeadIntermediateMaster: will next attempt to relocate up from %+v", *failedInstanceKey)

		var errs []error
		var relocatedSlaves [](*inst.Instance)
		relocatedSlaves, successorInstance, err, errs = inst.RelocateSlaves(failedInstanceKey, &analysisEntry.AnalyzedInstanceMasterKey, "")

		if len(relocatedSlaves) > 0 {
			actionTaken = true
			log.Debugf("topology_recovery: - RecoverDeadIntermediateMaster: relocated up to %+v", successorInstance.Key)
			inst.AuditOperation("recover-dead-intermediate-master", failedInstanceKey, fmt.Sprintf("Done. Relocated slaves under: %+v %d errors: %+v", successorInstance.Key, len(errs), errs))
		} else {
			err = log.Errorf("topology_recovery: RecoverDeadIntermediateMaster failed to match up any slave from %+v", *failedInstanceKey)
		}
	}
	if successorInstance != nil {
		ResolveRecovery(failedInstanceKey, &successorInstance.Key)
	} else {
		ResolveRecovery(failedInstanceKey, nil)
	}
	return actionTaken, successorInstance, err
}

func RecoverDeadMaster(analysisEntry inst.ReplicationAnalysis, skipProcesses bool) (promotedSlave *inst.Instance, lostSlaves [](*inst.Instance), err error) {
	failedInstanceKey := &analysisEntry.AnalyzedInstanceKey
	if ok, err := AttemptRecoveryRegistration(&analysisEntry); !ok {
		log.Debugf("topology_recovery: found an active or recent recovery on %+v. Will not issue another RecoverDeadMaster.", *failedInstanceKey)
		return nil, lostSlaves, err
	}

	inst.AuditOperation("recover-dead-master", failedInstanceKey, "problem found; will recover")
	if !skipProcesses {
		if err := executeProcesses(config.Config.PreFailoverProcesses, "PreFailoverProcesses", analysisEntry, nil, emptySlavesList, true); err != nil {
			return nil, lostSlaves, err
		}
	}

	log.Debugf("topology_recovery: RecoverDeadMaster: will recover %+v", *failedInstanceKey)

	var masterRecoveryType MasterRecoveryType = MasterRecoveryPseudoGTID
	if (analysisEntry.OracleGTIDImmediateTopology || analysisEntry.MariaDBGTIDImmediateTopology) && !analysisEntry.PseudoGTIDImmediateTopology {
		masterRecoveryType = MasterRecoveryGTID
	} else if analysisEntry.BinlogServerImmediateTopology {
		masterRecoveryType = MasterRecoveryBinlogServer
	}
	log.Debugf("topology_recovery: RecoverDeadMaster: masterRecoveryType=%+v", masterRecoveryType)

	switch masterRecoveryType {
	case MasterRecoveryGTID:
		{
			lostSlaves, _, promotedSlave, err = inst.RegroupSlavesGTID(failedInstanceKey, true, nil)
		}
	case MasterRecoveryPseudoGTID:
		{
			lostSlaves, _, _, promotedSlave, err = inst.RegroupSlavesIncludingSubSlavesOfBinlogServers(failedInstanceKey, true, nil)
		}
	case MasterRecoveryBinlogServer:
		{
			promotedSlave, err = inst.RegroupSlavesBinlogServers(failedInstanceKey, true, nil)
		}
	}
	if promotedSlave != nil && len(lostSlaves) > 0 && config.Config.DetachLostSlavesAfterMasterFailover {
		log.Debugf("topology_recovery: - RecoverDeadMaster: lost %+v slaves during recovery process; detaching them", len(lostSlaves))
		go func() {
			for _, slave := range lostSlaves {
				slave := slave
				inst.DetachSlaveOperation(&slave.Key)
			}
		}()
	}
	if config.Config.MasterFailoverLostInstancesDowntimeMinutes > 0 {
		inst.BeginDowntime(failedInstanceKey, inst.GetMaintenanceOwner(), "RecoverDeadMaster indicates this instance is lost", config.Config.MasterFailoverLostInstancesDowntimeMinutes*60)
		for _, slave := range lostSlaves {
			slave := slave
			inst.BeginDowntime(&slave.Key, inst.GetMaintenanceOwner(), "RecoverDeadMaster indicates this instance is lost", config.Config.MasterFailoverLostInstancesDowntimeMinutes*60)
		}
	}

	if promotedSlave == nil {
		log.Debugf("topology_recovery: - RecoverDeadMaster: Failure: no slave promoted.")
		inst.AuditOperation("recover-dead-master", failedInstanceKey, "Failure: no slave promoted.")
	} else {
		log.Debugf("topology_recovery: - RecoverDeadMaster: promoted slave is %+v", promotedSlave.Key)
		inst.AuditOperation("recover-dead-master", failedInstanceKey, fmt.Sprintf("master: %+v", promotedSlave.Key))
	}
	return promotedSlave, lostSlaves, err
}

// RecoverDeadCoMaster recovers a dead co-master, complete logic inside
func RecoverDeadCoMaster(topologyRecovery *TopologyRecovery, skipProcesses bool) (promotedSlave *inst.Instance, lostSlaves [](*inst.Instance), err error) {
	analysisEntry := &topologyRecovery.AnalysisEntry
	failedInstanceKey := &analysisEntry.AnalyzedInstanceKey
	otherCoMasterKey := &analysisEntry.AnalyzedInstanceMasterKey
	otherCoMaster, found, _ := inst.ReadInstance(otherCoMasterKey)
	if otherCoMaster == nil || !found {
		return nil, lostSlaves, topologyRecovery.AddError(log.Errorf("RecoverDeadCoMaster: could not read info for co-master %+v of %+v", *otherCoMasterKey, *failedInstanceKey))
	}
	inst.AuditOperation("recover-dead-co-master", failedInstanceKey, "problem found; will recover")
	if !skipProcesses {
		if err := executeProcesses(config.Config.PreFailoverProcesses, "PreFailoverProcesses", topologyRecovery, true); err != nil {
			return nil, lostSlaves, topologyRecovery.AddError(err)
		}
	}

	log.Debugf("topology_recovery: RecoverDeadCoMaster: will recover %+v", *failedInstanceKey)

	var coMasterRecoveryType MasterRecoveryType = MasterRecoveryPseudoGTID
	if analysisEntry.OracleGTIDImmediateTopology || analysisEntry.MariaDBGTIDImmediateTopology {
		coMasterRecoveryType = MasterRecoveryGTID
	}

	log.Debugf("topology_recovery: RecoverDeadCoMaster: coMasterRecoveryType=%+v", coMasterRecoveryType)

	switch coMasterRecoveryType {
	case MasterRecoveryGTID:
		{
			lostSlaves, _, promotedSlave, err = inst.RegroupSlavesGTID(failedInstanceKey, true, nil)
		}
	case MasterRecoveryPseudoGTID:
		{
			lostSlaves, _, _, promotedSlave, err = inst.RegroupSlavesPseudoGTIDIncludingSubSlavesOfBinlogServers(failedInstanceKey, true, nil, &topologyRecovery.PostponedFunctionsContainer)
		}
	}
	topologyRecovery.AddError(err)

	mustPromoteOtherCoMaster := config.Config.CoMasterRecoveryMustPromoteOtherCoMaster
	if !otherCoMaster.ReadOnly {
		log.Debugf("topology_recovery: RecoverDeadCoMaster: other co-master %+v is writeable hence has to be promoted", otherCoMaster.Key)
		mustPromoteOtherCoMaster = true
	}
	log.Debugf("topology_recovery: RecoverDeadCoMaster: mustPromoteOtherCoMaster? %+v", mustPromoteOtherCoMaster)

	if promotedSlave != nil {
		topologyRecovery.ParticipatingInstanceKeys.AddKey(promotedSlave.Key)
		if mustPromoteOtherCoMaster {
			log.Debugf("topology_recovery: mustPromoteOtherCoMaster. Verifying that %+v is/can be promoted", *otherCoMasterKey)
			promotedSlave, err = replacePromotedSlaveWithCandidate(failedInstanceKey, promotedSlave, otherCoMasterKey)
		} else {
			// We are allowed to promote any server
			promotedSlave, err = replacePromotedSlaveWithCandidate(failedInstanceKey, promotedSlave, nil)

			if promotedSlave.DataCenter == otherCoMaster.DataCenter &&
				promotedSlave.PhysicalEnvironment == otherCoMaster.PhysicalEnvironment && false {
				// and _still_ we prefer to promote the co-master! They're in same env & DC so no worries about geo issues!
				promotedSlave, err = replacePromotedSlaveWithCandidate(failedInstanceKey, promotedSlave, otherCoMasterKey)
			}
		}
		topologyRecovery.AddError(err)
	}
	if promotedSlave != nil {
		if mustPromoteOtherCoMaster && !promotedSlave.Key.Equals(otherCoMasterKey) {
			topologyRecovery.AddError(log.Errorf("RecoverDeadCoMaster: could not manage to promote other-co-master %+v; was only able to promote %+v; CoMasterRecoveryMustPromoteOtherCoMaster is true, therefore failing", *otherCoMasterKey, promotedSlave.Key))
			promotedSlave = nil
		}
	}
	if promotedSlave != nil {
		topologyRecovery.ParticipatingInstanceKeys.AddKey(promotedSlave.Key)
	}

	// OK, we may have someone promoted. Either this was the other co-master or another slave.
	// Noting down that we DO NOT attempt to set a new co-master topology. We are good with remaining with a single master.
	// I tried solving the "let's promote a slave and create a new co-master setup" but this turns so complex due to various factors.
	// I see this as risky and not worth the questionable benefit.
	// Maybe future me is a smarter person and finds a simple solution. Unlikely. I'm getting dumber.
	//
	// ...
	// Now that we're convinved, take a look at what we can be left with:
	// Say we started with M1<->M2<-S1, with M2 failing, and we promoted S1.
	// We now have M1->S1 (because S1 is promoted), S1->M2 (because that's what it remembers), M2->M1 (because that's what it remembers)
	// !! This is an evil 3-node circle that must be broken.
	// config.Config.ApplyMySQLPromotionAfterMasterFailover, if true, will cause it to break, because we would RESET SLAVE on S1
	// but we want to make sure the circle is broken no matter what.
	// So in the case we promoted not-the-other-co-master, we issue a detach-slave-master-host, which is a reversible operation
	if promotedSlave != nil && !promotedSlave.Key.Equals(otherCoMasterKey) {
		_, err = inst.DetachSlaveMasterHost(&promotedSlave.Key)
		topologyRecovery.AddError(log.Errore(err))
	}

	if promotedSlave != nil && len(lostSlaves) > 0 && config.Config.DetachLostSlavesAfterMasterFailover {
		postponedFunction := func() error {
			log.Debugf("topology_recovery: - RecoverDeadCoMaster: lost %+v slaves during recovery process; detaching them", len(lostSlaves))
			for _, slave := range lostSlaves {
				slave := slave
				inst.DetachSlaveOperation(&slave.Key)
			}
			return nil
		}
		topologyRecovery.AddPostponedFunction(postponedFunction)
//.........这里部分代码省略.........

// RecoverDeadIntermediateMaster performs intermediate master recovery; complete logic inside
func RecoverDeadIntermediateMaster(topologyRecovery *TopologyRecovery, skipProcesses bool) (successorInstance *inst.Instance, err error) {
	analysisEntry := &topologyRecovery.AnalysisEntry
	failedInstanceKey := &analysisEntry.AnalyzedInstanceKey
	recoveryResolved := false

	inst.AuditOperation("recover-dead-intermediate-master", failedInstanceKey, "problem found; will recover")
	if !skipProcesses {
		if err := executeProcesses(config.Config.PreFailoverProcesses, "PreFailoverProcesses", topologyRecovery, true); err != nil {
			return nil, topologyRecovery.AddError(err)
		}
	}

	intermediateMasterInstance, _, err := inst.ReadInstance(failedInstanceKey)
	if err != nil {
		return nil, topologyRecovery.AddError(err)
	}
	// Find possible candidate
	candidateSiblingOfIntermediateMaster, err := GetCandidateSiblingOfIntermediateMaster(intermediateMasterInstance)
	relocateSlavesToCandidateSibling := func() {
		if candidateSiblingOfIntermediateMaster == nil {
			return
		}
		// We have a candidate
		log.Debugf("topology_recovery: - RecoverDeadIntermediateMaster: will attempt a candidate intermediate master: %+v", candidateSiblingOfIntermediateMaster.Key)
		relocatedSlaves, candidateSibling, err, errs := inst.RelocateSlaves(failedInstanceKey, &candidateSiblingOfIntermediateMaster.Key, "")
		topologyRecovery.AddErrors(errs)
		topologyRecovery.ParticipatingInstanceKeys.AddKey(candidateSiblingOfIntermediateMaster.Key)

		if len(relocatedSlaves) == 0 {
			log.Debugf("topology_recovery: - RecoverDeadIntermediateMaster: failed to move any slave to candidate intermediate master (%+v)", candidateSibling.Key)
			return
		}
		if err != nil || len(errs) > 0 {
			log.Debugf("topology_recovery: - RecoverDeadIntermediateMaster: move to candidate intermediate master (%+v) did not complete: %+v", candidateSibling.Key, err)
			return
		}
		if err == nil {
			recoveryResolved = true
			successorInstance = candidateSibling

			inst.AuditOperation("recover-dead-intermediate-master", failedInstanceKey, fmt.Sprintf("Relocated %d slaves under candidate sibling: %+v; %d errors: %+v", len(relocatedSlaves), candidateSibling.Key, len(errs), errs))
		}
	}
	// Plan A: find a replacement intermediate master in same Data Center
	if candidateSiblingOfIntermediateMaster != nil && candidateSiblingOfIntermediateMaster.DataCenter == intermediateMasterInstance.DataCenter {
		relocateSlavesToCandidateSibling()
	}
	if !recoveryResolved {
		log.Debugf("topology_recovery: - RecoverDeadIntermediateMaster: will next attempt regrouping of slaves")
		// Plan B: regroup (we wish to reduce cross-DC replication streams)
		_, _, _, regroupPromotedSlave, err := inst.RegroupSlaves(failedInstanceKey, true, nil, nil)
		if err != nil {
			topologyRecovery.AddError(err)
			log.Debugf("topology_recovery: - RecoverDeadIntermediateMaster: regroup failed on: %+v", err)
		}
		if regroupPromotedSlave != nil {
			topologyRecovery.ParticipatingInstanceKeys.AddKey(regroupPromotedSlave.Key)
		}
		// Plan C: try replacement intermediate master in other DC...
		if candidateSiblingOfIntermediateMaster != nil && candidateSiblingOfIntermediateMaster.DataCenter != intermediateMasterInstance.DataCenter {
			log.Debugf("topology_recovery: - RecoverDeadIntermediateMaster: will next attempt relocating to another DC server")
			relocateSlavesToCandidateSibling()
		}
	}
	if !recoveryResolved {
		// Do we still have leftovers? Some slaves couldn't move? Couldn't regroup? Only left with regroup's resulting leader?
		// nothing moved?
		// We don't care much if regroup made it or not. We prefer that it made it, in whcih case we only need to relocate up
		// one slave, but the operation is still valid if regroup partially/completely failed. We just promote anything
		// not regrouped.
		// So, match up all that's left, plan D
		log.Debugf("topology_recovery: - RecoverDeadIntermediateMaster: will next attempt to relocate up from %+v", *failedInstanceKey)

		var errs []error
		var relocatedSlaves [](*inst.Instance)
		relocatedSlaves, successorInstance, err, errs = inst.RelocateSlaves(failedInstanceKey, &analysisEntry.AnalyzedInstanceMasterKey, "")
		topologyRecovery.AddErrors(errs)
		topologyRecovery.ParticipatingInstanceKeys.AddKey(analysisEntry.AnalyzedInstanceMasterKey)

		if len(relocatedSlaves) > 0 {
			recoveryResolved = true
			inst.AuditOperation("recover-dead-intermediate-master", failedInstanceKey, fmt.Sprintf("Relocated slaves under: %+v %d errors: %+v", successorInstance.Key, len(errs), errs))
		} else {
			err = log.Errorf("topology_recovery: RecoverDeadIntermediateMaster failed to match up any slave from %+v", *failedInstanceKey)
			topologyRecovery.AddError(err)
		}
	}
	if !recoveryResolved {
		successorInstance = nil
	}
	ResolveRecovery(topologyRecovery, successorInstance)
	return successorInstance, err
}

// RecoverDeadMaster recovers a dead master, complete logic inside
func RecoverDeadMaster(topologyRecovery *TopologyRecovery, skipProcesses bool) (promotedSlave *inst.Instance, lostSlaves [](*inst.Instance), err error) {
	analysisEntry := &topologyRecovery.AnalysisEntry
	failedInstanceKey := &analysisEntry.AnalyzedInstanceKey

	inst.AuditOperation("recover-dead-master", failedInstanceKey, "problem found; will recover")
	if !skipProcesses {
		if err := executeProcesses(config.Config.PreFailoverProcesses, "PreFailoverProcesses", topologyRecovery, true); err != nil {
			return nil, lostSlaves, topologyRecovery.AddError(err)
		}
	}

	log.Debugf("topology_recovery: RecoverDeadMaster: will recover %+v", *failedInstanceKey)

	var masterRecoveryType MasterRecoveryType = MasterRecoveryPseudoGTID
	if analysisEntry.OracleGTIDImmediateTopology || analysisEntry.MariaDBGTIDImmediateTopology {
		masterRecoveryType = MasterRecoveryGTID
	} else if analysisEntry.BinlogServerImmediateTopology {
		masterRecoveryType = MasterRecoveryBinlogServer
	}
	log.Debugf("topology_recovery: RecoverDeadMaster: masterRecoveryType=%+v", masterRecoveryType)

	switch masterRecoveryType {
	case MasterRecoveryGTID:
		{
			lostSlaves, _, promotedSlave, err = inst.RegroupSlavesGTID(failedInstanceKey, true, nil)
		}
	case MasterRecoveryPseudoGTID:
		{
			lostSlaves, _, _, promotedSlave, err = inst.RegroupSlavesPseudoGTIDIncludingSubSlavesOfBinlogServers(failedInstanceKey, true, nil, &topologyRecovery.PostponedFunctionsContainer)
		}
	case MasterRecoveryBinlogServer:
		{
			promotedSlave, err = recoverDeadMasterInBinlogServerTopology(topologyRecovery)
		}
	}
	topologyRecovery.AddError(err)

	if promotedSlave != nil && len(lostSlaves) > 0 && config.Config.DetachLostSlavesAfterMasterFailover {
		postponedFunction := func() error {
			log.Debugf("topology_recovery: - RecoverDeadMaster: lost %+v slaves during recovery process; detaching them", len(lostSlaves))
			for _, slave := range lostSlaves {
				slave := slave
				inst.DetachSlaveOperation(&slave.Key)
			}
			return nil
		}
		topologyRecovery.AddPostponedFunction(postponedFunction)
	}
	if config.Config.MasterFailoverLostInstancesDowntimeMinutes > 0 {
		postponedFunction := func() error {
			inst.BeginDowntime(failedInstanceKey, inst.GetMaintenanceOwner(), "RecoverDeadMaster indicates this instance is lost", config.Config.MasterFailoverLostInstancesDowntimeMinutes*60)
			for _, slave := range lostSlaves {
				slave := slave
				inst.BeginDowntime(&slave.Key, inst.GetMaintenanceOwner(), "RecoverDeadMaster indicates this instance is lost", config.Config.MasterFailoverLostInstancesDowntimeMinutes*60)
			}
			return nil
		}
		topologyRecovery.AddPostponedFunction(postponedFunction)
	}

	if promotedSlave == nil {
		inst.AuditOperation("recover-dead-master", failedInstanceKey, "Failure: no slave promoted.")
	} else {
		inst.AuditOperation("recover-dead-master", failedInstanceKey, fmt.Sprintf("promoted slave: %+v", promotedSlave.Key))
	}
	return promotedSlave, lostSlaves, err
}

// DiscoverInstance will attempt discovering an instance (unless it is already up to date) and will
// list down its master and slaves (if any) for further discovery.
func DiscoverInstance(instanceKey inst.InstanceKey) {
	instanceKey.Formalize()
	if !instanceKey.IsValid() {
		return
	}

	instance, found, err := inst.ReadInstance(&instanceKey)

	if found && instance.IsUpToDate && instance.IsLastCheckValid {
		// we've already discovered this one. Skip!
		goto Cleanup
	}
	// First we've ever heard of this instance. Continue investigation:
	instance, err = inst.ReadTopologyInstance(&instanceKey)
	// panic can occur (IO stuff). Therefore it may happen
	// that instance is nil. Check it.
	if err != nil || instance == nil {
		log.Warningf("instance is nil in DiscoverInstance. key=%+v, error=%+v", instanceKey, err)
		goto Cleanup
	}

	log.Debugf("Discovered host: %+v, master: %+v", instance.Key, instance.MasterKey)

	// Investigate slaves:
	for _, slaveKey := range instance.SlaveHosts.GetInstanceKeys() {
		discoveryInstanceKeys <- slaveKey
	}
	// Investigate master:
	discoveryInstanceKeys <- instance.MasterKey

Cleanup:
}

// Start discovery begins a one time asynchronuous discovery process for the given
// instance and all of its topology connected instances.
// That is, the instance will be investigated for master and slaves, and the routines will follow on
// each and every such found master/slave.
// In essense, assuming all slaves in a replication topology are running, and given a single instance
// in such topology, this function will detect the entire topology.
func StartDiscovery(instanceKey inst.InstanceKey) {
	log.Infof("Starting discovery at %+v", instanceKey)
	pendingTokens := make(chan bool, maxConcurrency)
	completedTokens := make(chan bool, maxConcurrency)

	AccountedDiscoverInstance(instanceKey, pendingTokens, completedTokens)
	go handleDiscoveryRequests(pendingTokens, completedTokens)

	// Block until all are complete
	for {
		select {
		case <-pendingTokens:
			<-completedTokens
		default:
			inst.AuditOperation("start-discovery", &instanceKey, "")
			return
		}
	}
}

// ContinuousDiscovery starts an asynchronuous infinite discovery process where instances are
// periodically investigated and their status captured, and long since unseen instances are
// purged and forgotten.
func ContinuousDiscovery() {
	log.Infof("Starting continuous discovery")
	inst.LoadHostnameResolveCacheFromDatabase()
	go handleDiscoveryRequests(nil, nil)
	tick := time.Tick(time.Duration(config.Config.DiscoveryPollSeconds) * time.Second)
	forgetUnseenTick := time.Tick(time.Minute)
	recoverTick := time.Tick(10 * time.Second)

	var snapshotTopologiesTick <-chan time.Time
	if config.Config.SnapshotTopologiesIntervalHours > 0 {
		snapshotTopologiesTick = time.Tick(time.Duration(config.Config.SnapshotTopologiesIntervalHours) * time.Hour)
	}

	elected := false
	_ = CreateElectionAnchor(false)
	for {
		select {
		case <-tick:
			if elected, _ = AttemptElection(); elected {
				instanceKeys, _ := inst.ReadOutdatedInstanceKeys()
				log.Debugf("outdated keys: %+v", instanceKeys)
				for _, instanceKey := range instanceKeys {
					discoveryInstanceKeys <- instanceKey
				}
			} else {
				log.Debugf("Not elected as active node; polling")
			}
		case <-forgetUnseenTick:
			// See if we should also forget objects (lower frequency)
			go func() {
				if elected {
					inst.ForgetLongUnseenInstances()
					inst.ForgetUnseenInstancesDifferentlyResolved()
					inst.ForgetExpiredHostnameResolves()
					inst.DeleteInvalidHostnameResolves()
					inst.ReviewUnseenInstances()
//.........这里部分代码省略.........

// RecoverDeadCoMaster recovers a dead co-master, complete logic inside
func RecoverDeadCoMaster(topologyRecovery *TopologyRecovery, skipProcesses bool) (otherCoMaster *inst.Instance, lostSlaves [](*inst.Instance), err error) {
	analysisEntry := &topologyRecovery.AnalysisEntry
	failedInstanceKey := &analysisEntry.AnalyzedInstanceKey
	otherCoMasterKey := &analysisEntry.AnalyzedInstanceMasterKey

	inst.AuditOperation("recover-dead-co-master", failedInstanceKey, "problem found; will recover")
	if !skipProcesses {
		if err := executeProcesses(config.Config.PreFailoverProcesses, "PreFailoverProcesses", topologyRecovery, true); err != nil {
			return nil, lostSlaves, topologyRecovery.AddError(err)
		}
	}

	log.Debugf("topology_recovery: RecoverDeadCoMaster: will recover %+v", *failedInstanceKey)

	var coMasterRecoveryType MasterRecoveryType = MasterRecoveryPseudoGTID
	if (analysisEntry.OracleGTIDImmediateTopology || analysisEntry.MariaDBGTIDImmediateTopology) && !analysisEntry.PseudoGTIDImmediateTopology {
		coMasterRecoveryType = MasterRecoveryGTID
	}

	log.Debugf("topology_recovery: RecoverDeadCoMaster: coMasterRecoveryType=%+v", coMasterRecoveryType)

	var promotedSlave *inst.Instance
	switch coMasterRecoveryType {
	case MasterRecoveryGTID:
		{
			lostSlaves, _, promotedSlave, err = inst.RegroupSlavesGTID(failedInstanceKey, true, nil)
		}
	case MasterRecoveryPseudoGTID:
		{
			lostSlaves, _, _, promotedSlave, err = inst.RegroupSlavesPseudoGTIDIncludingSubSlavesOfBinlogServers(failedInstanceKey, true, nil, &topologyRecovery.PostponedFunctionsContainer)
		}
	}
	topologyRecovery.AddError(err)

	if promotedSlave != nil {
		topologyRecovery.ParticipatingInstanceKeys.AddKey(promotedSlave.Key)
		promotedSlave, err = replacePromotedSlaveWithCandidate(failedInstanceKey, promotedSlave, otherCoMasterKey)
		topologyRecovery.AddError(err)
	}
	if promotedSlave != nil {
		if promotedSlave.Key.Equals(otherCoMasterKey) {
			topologyRecovery.ParticipatingInstanceKeys.AddKey(*otherCoMasterKey)
			otherCoMaster = promotedSlave
		} else {
			err = log.Errorf("RecoverDeadCoMaster: could not manage to promote other-co-master %+v; was only able to promote %+v", *otherCoMasterKey, promotedSlave.Key)
			promotedSlave = nil
		}
	}

	if promotedSlave != nil && len(lostSlaves) > 0 && config.Config.DetachLostSlavesAfterMasterFailover {
		postponedFunction := func() error {
			log.Debugf("topology_recovery: - RecoverDeadCoMaster: lost %+v slaves during recovery process; detaching them", len(lostSlaves))
			for _, slave := range lostSlaves {
				slave := slave
				inst.DetachSlaveOperation(&slave.Key)
			}
			return nil
		}
		topologyRecovery.AddPostponedFunction(postponedFunction)
	}
	if config.Config.MasterFailoverLostInstancesDowntimeMinutes > 0 {
		postponedFunction := func() error {
			inst.BeginDowntime(failedInstanceKey, inst.GetMaintenanceOwner(), "RecoverDeadCoMaster indicates this instance is lost", config.Config.MasterFailoverLostInstancesDowntimeMinutes*60)
			for _, slave := range lostSlaves {
				slave := slave
				inst.BeginDowntime(&slave.Key, inst.GetMaintenanceOwner(), "RecoverDeadCoMaster indicates this instance is lost", config.Config.MasterFailoverLostInstancesDowntimeMinutes*60)
			}
			return nil
		}
		topologyRecovery.AddPostponedFunction(postponedFunction)
	}

	return otherCoMaster, lostSlaves, err
}

// discoverInstance will attempt discovering an instance (unless it is already up to date) and will
// list down its master and slaves (if any) for further discovery.
func discoverInstance(instanceKey inst.InstanceKey) {
	instanceKey.Formalize()
	if !instanceKey.IsValid() {
		return
	}

	instance, found, err := inst.ReadInstance(&instanceKey)

	if found && instance.IsUpToDate && instance.IsLastCheckValid {
		// we've already discovered this one. Skip!
		goto Cleanup
	}
	discoveriesCounter.Inc(1)
	// First we've ever heard of this instance. Continue investigation:
	instance, err = inst.ReadTopologyInstance(&instanceKey)
	// panic can occur (IO stuff). Therefore it may happen
	// that instance is nil. Check it.
	if err != nil || instance == nil {
		failedDiscoveriesCounter.Inc(1)
		log.Warningf("instance is nil in discoverInstance. key=%+v, error=%+v", instanceKey, err)
		goto Cleanup
	}

	log.Debugf("Discovered host: %+v, master: %+v", instance.Key, instance.MasterKey)

	if !isElectedNode {
		// Maybe this node was elected before, but isn't elected anymore.
		// If not elected, stop drilling down to further investigate slaves.
		return
	}

	// Investigate slaves:
	for _, slaveKey := range instance.SlaveHosts.GetInstanceKeys() {
		discoveryInstanceKeys <- slaveKey
	}
	// Investigate master:
	discoveryInstanceKeys <- instance.MasterKey

Cleanup:
}

// Start discovery begins a one time asynchronuous discovery process for the given
// instance and all of its topology connected instances.
// That is, the instance will be investigated for master and slaves, and the routines will follow on
// each and every such found master/slave.
// In essense, assuming all slaves in a replication topology are running, and given a single instance
// in such topology, this function will detect the entire topology.
func StartDiscovery(instanceKey inst.InstanceKey) {
	log.Infof("Starting discovery at %+v", instanceKey)
	pendingTokens := make(chan bool, maxConcurrency)
	completedTokens := make(chan bool, maxConcurrency)

	accountedDiscoverInstance(instanceKey, pendingTokens, completedTokens)
	go handle