func (agent *ActionAgent) verifyServingAddrs(ctx context.Context) error {
	ti := agent.Tablet()
	if !topo.IsRunningQueryService(ti.Type) {
		return nil
	}

	// Check to see our address is registered in the right place.
	return topotools.UpdateTabletEndpoints(ctx, agent.TopoServer, ti.Tablet)
}

// runHealthCheck takes the action mutex, runs the health check,
// and if we need to change our state, do it.
// If we are the master, we don't change our type, healthy or not.
// If we are not the master, we change to spare if not healthy,
// or to the passed in targetTabletType if healthy.
//
// Note we only update the topo record if we need to, that is if our type or
// health details changed.
func (agent *ActionAgent) runHealthCheck(targetTabletType pbt.TabletType) {
	agent.actionMutex.Lock()
	defer agent.actionMutex.Unlock()

	// read the current tablet record and tablet control
	agent.mutex.Lock()
	tablet := agent._tablet
	tabletControl := agent._tabletControl
	agent.mutex.Unlock()

	// figure out if we should be running the query service
	shouldQueryServiceBeRunning := false
	var blacklistedTables []string
	if topo.IsRunningQueryService(targetTabletType) && !agent.BinlogPlayerMap.isRunningFilteredReplication() {
		shouldQueryServiceBeRunning = true
		if tabletControl != nil {
			blacklistedTables = tabletControl.BlacklistedTables
			if tabletControl.DisableQueryService {
				shouldQueryServiceBeRunning = false
			}
		}
	}

	// run the health check
	typeForHealthCheck := targetTabletType
	if tablet.Type == pbt.TabletType_MASTER {
		typeForHealthCheck = pbt.TabletType_MASTER
	}
	replicationDelay, err := agent.HealthReporter.Report(topo.IsSlaveType(typeForHealthCheck), shouldQueryServiceBeRunning)
	health := make(map[string]string)
	if err == nil {
		if replicationDelay > *unhealthyThreshold {
			err = fmt.Errorf("reported replication lag: %v higher than unhealthy threshold: %v", replicationDelay.Seconds(), unhealthyThreshold.Seconds())
		} else if replicationDelay > *degradedThreshold {
			health[topo.ReplicationLag] = topo.ReplicationLagHigh
		}
	}
	agent.lastHealthMapCount.Set(int64(len(health)))

	// Figure out if we should be running QueryService, see if we are,
	// and reconcile.
	if err != nil {
		if tablet.Type != pbt.TabletType_WORKER {
			// We are not healthy and must shut down QueryService.
			// At the moment, the only exception to this are "worker" tablets which
			// still must serve queries e.g. as source tablet during a "SplitClone".
			shouldQueryServiceBeRunning = false
		}
	}
	isQueryServiceRunning := agent.QueryServiceControl.IsServing()
	if shouldQueryServiceBeRunning {
		if !isQueryServiceRunning {
			// send the type we want to be, not the type we are
			currentType := tablet.Type
			if tablet.Type == pbt.TabletType_SPARE {
				tablet.Type = targetTabletType
			}

			// we remember this new possible error
			err = agent.allowQueries(tablet.Tablet, blacklistedTables)

			// restore the current type
			tablet.Type = currentType
		}
	} else {
		if isQueryServiceRunning {
			// we are not healthy or should not be running the
			// query service, shut it down.
			agent.stopQueryService()
		}
	}

	// save the health record
	record := &HealthRecord{
		Error:            err,
		ReplicationDelay: replicationDelay,
		Time:             time.Now(),
	}
	agent.History.Add(record)

	// try to figure out the mysql port if we don't have it yet
	if _, ok := tablet.PortMap["mysql"]; !ok {
		// we don't know the port, try to get it from mysqld
		mysqlPort, err := agent.MysqlDaemon.GetMysqlPort()
		if err != nil {
			// Don't log if we're already in a waiting-for-mysql state.
			agent.mutex.Lock()
			if !agent._waitingForMysql {
				log.Warningf("Can't get mysql port, won't populate Tablet record in topology (will retry silently at healthcheck interval %v): %v", *healthCheckInterval, err)
				agent._waitingForMysql = true
			}
			agent.mutex.Unlock()
//.........这里部分代码省略.........

// runHealthCheck takes the action mutex, runs the health check,
// and if we need to change our state, do it.
// If we are the master, we don't change our type, healthy or not.
// If we are not the master, we change to spare if not healthy,
// or to the passed in targetTabletType if healthy.
//
// Note we only update the topo record if we need to, that is if our type or
// health details changed.
func (agent *ActionAgent) runHealthCheck(targetTabletType topo.TabletType) {
	agent.actionMutex.Lock()
	defer agent.actionMutex.Unlock()

	// read the current tablet record and blacklisted tables
	agent.mutex.Lock()
	tablet := agent._tablet
	blacklistedTables := agent._blacklistedTables
	agent.mutex.Unlock()

	// run the health check
	typeForHealthCheck := targetTabletType
	if tablet.Type == topo.TYPE_MASTER {
		typeForHealthCheck = topo.TYPE_MASTER
	}
	health, err := health.Run(typeForHealthCheck)

	// Figure out if we should be running QueryService. If we should,
	// and we aren't, and we're otherwise healthy, try to start it.
	if err == nil && topo.IsRunningQueryService(targetTabletType) && agent.BinlogPlayerMap.size() == 0 {
		err = agent.allowQueries(tablet.Tablet, blacklistedTables)
	}

	// save the health record
	record := &HealthRecord{
		Error:  err,
		Result: health,
		Time:   time.Now(),
	}
	agent.History.Add(record)

	// try to figure out the mysql port if we don't have it yet
	if _, ok := tablet.Portmap["mysql"]; !ok {
		// we don't know the port, try to get it from mysqld
		mysqlPort, err := agent.Mysqld.GetMysqlPort()
		if err != nil {
			// Don't log if we're already in a waiting-for-mysql state.
			agent.mutex.Lock()
			if !agent._waitingForMysql {
				log.Warningf("Can't get mysql port, won't populate Tablet record in topology (will retry silently at healthcheck interval %v): %v", *healthCheckInterval, err)
				agent._waitingForMysql = true
			}
			agent.mutex.Unlock()
		} else {
			log.Infof("Updating tablet mysql port to %v", mysqlPort)
			if err := agent.TopoServer.UpdateTabletFields(tablet.Alias, func(tablet *topo.Tablet) error {
				tablet.Portmap["mysql"] = mysqlPort
				return nil
			}); err != nil {
				log.Infof("Error updating mysql port in tablet record: %v", err)
				return
			}

			// save the port so we don't update it again next time
			// we do the health check.
			agent.mutex.Lock()
			agent._tablet.Portmap["mysql"] = mysqlPort
			agent._waitingForMysql = false
			agent.mutex.Unlock()
		}
	}

	// Update our topo.Server state, start with no change
	newTabletType := tablet.Type
	if err != nil {
		// The tablet is not healthy, let's see what we need to do
		if tablet.Type != targetTabletType {
			if tablet.Type != topo.TYPE_SPARE {
				// we only log if we're not in spare,
				// as the spare state is normal for a
				// failed health check.
				log.Infof("Tablet not healthy and in state %v, not changing it: %v", tablet.Type, err)
			}
			return
		}

		// Note that if the query service is running, we may
		// need to stop it. The post-action callback will do
		// it, and it will be done after we change our state,
		// so it's the right order, let it do it.
		log.Infof("Tablet not healthy, converting it from %v to spare: %v", targetTabletType, err)
		newTabletType = topo.TYPE_SPARE
	} else {
		// We are healthy, maybe with health, see if we need
		// to update the record. We only change from spare to
		// our target type.
		if tablet.Type == topo.TYPE_SPARE {
			newTabletType = targetTabletType
		}
		if tablet.Type == newTabletType && tablet.IsHealthEqual(health) {
			// no change in health, not logging anything,
			// and we're done
//.........这里部分代码省略.........

// changeCallback is run after every action that might
// have changed something in the tablet record.
func (agent *ActionAgent) changeCallback(ctx context.Context, oldTablet, newTablet *pbt.Tablet) error {
	span := trace.NewSpanFromContext(ctx)
	span.StartLocal("ActionAgent.changeCallback")
	defer span.Finish()

	allowQuery := topo.IsRunningQueryService(newTablet.Type)

	// Read the shard to get SourceShards / TabletControlMap if
	// we're going to use it.
	var shardInfo *topo.ShardInfo
	var tabletControl *pbt.Shard_TabletControl
	var blacklistedTables []string
	var err error
	var disallowQueryReason string
	if allowQuery {
		shardInfo, err = agent.TopoServer.GetShard(ctx, newTablet.Keyspace, newTablet.Shard)
		if err != nil {
			log.Errorf("Cannot read shard for this tablet %v, might have inaccurate SourceShards and TabletControls: %v", newTablet.Alias, err)
		} else {
			if newTablet.Type == pbt.TabletType_MASTER {
				if len(shardInfo.SourceShards) > 0 {
					allowQuery = false
					disallowQueryReason = "old master is still in shard info"
				}
			}
			if tc := shardInfo.GetTabletControl(newTablet.Type); tc != nil {
				if topo.InCellList(newTablet.Alias.Cell, tc.Cells) {
					if tc.DisableQueryService {
						allowQuery = false
						disallowQueryReason = "query service disabled by tablet control"
					}
					blacklistedTables = tc.BlacklistedTables
					tabletControl = tc
				}
			}
		}
	} else {
		disallowQueryReason = fmt.Sprintf("not a serving tablet type(%v)", newTablet.Type)
	}

	// Read the keyspace on masters to get ShardingColumnType,
	// for binlog replication, only if source shards are set.
	var keyspaceInfo *topo.KeyspaceInfo
	if newTablet.Type == pbt.TabletType_MASTER && shardInfo != nil && len(shardInfo.SourceShards) > 0 {
		keyspaceInfo, err = agent.TopoServer.GetKeyspace(ctx, newTablet.Keyspace)
		if err != nil {
			log.Errorf("Cannot read keyspace for this tablet %v: %v", newTablet.Alias, err)
			keyspaceInfo = nil
		}
	}

	if allowQuery {
		// There are a few transitions when we need to restart the query service:
		switch {
		// If either InitMaster or InitSlave was called, because those calls
		// (or a prior call to ResetReplication) may have silently broken the
		// rowcache invalidator by executing RESET MASTER.
		// Note that we don't care about fixing it after ResetReplication itself
		// since that call breaks everything on purpose, and we don't expect
		// anything to start working until either InitMaster or InitSlave.
		case agent.initReplication:
			agent.initReplication = false
			agent.stopQueryService("initialize replication")

		// Transitioning from replica to master, so clients that were already
		// connected don't keep on using the master as replica or rdonly.
		case newTablet.Type == pbt.TabletType_MASTER && oldTablet.Type != pbt.TabletType_MASTER:
			agent.stopQueryService("tablet promoted to master")

		// Having different parameters for the query service.
		// It needs to stop and restart with the new parameters.
		// That includes:
		//   - changing KeyRange
		//   - changing the BlacklistedTables list
		case (newTablet.KeyRange != oldTablet.KeyRange),
			!reflect.DeepEqual(blacklistedTables, agent.BlacklistedTables()):
			agent.stopQueryService("keyrange/blacklistedtables changed")
		}

		if err := agent.allowQueries(newTablet, blacklistedTables); err != nil {
			log.Errorf("Cannot start query service: %v", err)
		}
	} else {
		agent.stopQueryService(disallowQueryReason)
	}

	// save the tabletControl we've been using, so the background
	// healthcheck makes the same decisions as we've been making.
	agent.setTabletControl(tabletControl)

	// update stream needs to be started or stopped too
	if agent.DBConfigs != nil {
		if topo.IsRunningUpdateStream(newTablet.Type) {
			binlog.EnableUpdateStreamService(agent.DBConfigs.App.DbName, agent.MysqlDaemon)
		} else {
			binlog.DisableUpdateStreamService()
		}
	}
//.........这里部分代码省略.........

// runHealthCheck takes the action mutex, runs the health check,
// and if we need to change our state, do it.
// If we are the master, we don't change our type, healthy or not.
// If we are not the master, we change to spare if not healthy,
// or to the passed in targetTabletType if healthy.
//
// Note we only update the topo record if we need to, that is if our type or
// health details changed.
func (agent *ActionAgent) runHealthCheck(targetTabletType topo.TabletType, lockTimeout time.Duration) {
	agent.actionMutex.Lock()
	defer agent.actionMutex.Unlock()

	// read the current tablet record
	agent.mutex.Lock()
	tablet := agent._tablet
	agent.mutex.Unlock()

	// run the health check
	typeForHealthCheck := targetTabletType
	if tablet.Type == topo.TYPE_MASTER {
		typeForHealthCheck = topo.TYPE_MASTER
	}
	health, err := health.Run(typeForHealthCheck)

	// Figure out if we should be running QueryService. If we should,
	// and we aren't, and we're otherwise healthy, try to start it
	if err == nil && topo.IsRunningQueryService(targetTabletType) {
		err = agent.allowQueries(tablet.Tablet)
	}

	// save the health record
	record := &HealthRecord{
		Error:  err,
		Result: health,
		Time:   time.Now(),
	}
	agent.History.Add(record)

	// Update our topo.Server state, start with no change
	newTabletType := tablet.Type
	if err != nil {
		// The tablet is not healthy, let's see what we need to do
		if tablet.Type != targetTabletType {
			if tablet.Type != topo.TYPE_SPARE {
				// we onyl log if we're not in spare,
				// as the spare state is normal for a
				// failed health check.
				log.Infof("Tablet not healthy and in state %v, not changing it: %v", tablet.Type, err)
			}
			return
		}

		// Note that if the query service is running, we may
		// need to stop it. The post-action callback will do
		// it, and it will be done after we change our state,
		// so it's the right order, let it do it.
		log.Infof("Tablet not healthy, converting it from %v to spare: %v", targetTabletType, err)
		newTabletType = topo.TYPE_SPARE
	} else {
		// We are healthy, maybe with health, see if we need
		// to update the record. We only change from spare to
		// our target type.
		if tablet.Type == topo.TYPE_SPARE {
			newTabletType = targetTabletType
		}
		if tablet.Type == newTabletType && tablet.IsHealthEqual(health) {
			// no change in health, not logging anything,
			// and we're done
			return
		}

		// we need to update our state
		log.Infof("Updating tablet record as healthy type %v -> %v with health details %v -> %v", tablet.Type, newTabletType, tablet.Health, health)
		agent.lastHealthMapCount.Set(int64(len(health)))
	}

	// Change the Type, update the health. Note we pass in a map
	// that's not nil, meaning if it's empty, we will clear it.
	if err := topotools.ChangeType(agent.TopoServer, tablet.Alias, newTabletType, health, true /*runHooks*/); err != nil {
		log.Infof("Error updating tablet record: %v", err)
		return
	}

	// Rebuild the serving graph in our cell, only if we're dealing with
	// a serving type
	if err := agent.rebuildShardIfNeeded(tablet, targetTabletType, lockTimeout); err != nil {
		log.Warningf("rebuildShardIfNeeded failed, not running post action callbacks: %v", err)
		return
	}

	// run the post action callbacks
	agent.afterAction("healthcheck", false /* reloadSchema */)
}

// runHealthCheck takes the action mutex, runs the health check,
// and if we need to change our state, do it.
// If we are the master, we don't change our type, healthy or not.
// If we are not the master, we change to spare if not healthy,
// or to the passed in targetTabletType if healthy.
//
// Note we only update the topo record if we need to, that is if our type or
// health details changed.
//
// This will not change the BinlogPlayerMap, but if it is not empty,
// we will think we should not be running the query service.
//
// This will not change the TabletControl record, but will use it
// to see if we should be running the query service.
func (agent *ActionAgent) runHealthCheck(targetTabletType topodatapb.TabletType) {
	agent.actionMutex.Lock()
	defer agent.actionMutex.Unlock()

	// read the current tablet record and tablet control
	agent.mutex.Lock()
	tablet := proto.Clone(agent._tablet).(*topodatapb.Tablet)
	tabletControl := proto.Clone(agent._tabletControl).(*topodatapb.Shard_TabletControl)
	agent.mutex.Unlock()

	// figure out if we should be running the query service
	shouldBeServing := false
	if topo.IsRunningQueryService(targetTabletType) && !agent.BinlogPlayerMap.isRunningFilteredReplication() {
		shouldBeServing = true
		if tabletControl != nil {
			if tabletControl.DisableQueryService {
				shouldBeServing = false
			}
		}
	}

	// run the health check
	isSlaveType := true
	if tablet.Type == topodatapb.TabletType_MASTER {
		isSlaveType = false
	}
	// Remember the health error as healthErr to be sure we don't accidentally
	// overwrite it with some other err.
	replicationDelay, healthErr := agent.HealthReporter.Report(isSlaveType, shouldBeServing)
	health := make(map[string]string)
	if healthErr == nil {
		if replicationDelay > *unhealthyThreshold {
			healthErr = fmt.Errorf("reported replication lag: %v higher than unhealthy threshold: %v", replicationDelay.Seconds(), unhealthyThreshold.Seconds())
		} else if replicationDelay > *degradedThreshold {
			health[topo.ReplicationLag] = topo.ReplicationLagHigh
		}
	}
	agent.lastHealthMapCount.Set(int64(len(health)))

	// Figure out if we should be running QueryService, see if we are,
	// and reconcile.
	if healthErr != nil {
		if tablet.Type != topodatapb.TabletType_WORKER {
			// We are not healthy and must shut down QueryService.
			// At the moment, the only exception to this are "worker" tablets which
			// still must serve queries e.g. as source tablet during a "SplitClone".
			shouldBeServing = false
		}
	}
	isServing := agent.QueryServiceControl.IsServing()
	if shouldBeServing {
		if !isServing {
			// It might be that we're ready to serve, but we just need to start
			// queryservice. Send the type we want to be, not the type we are.
			desiredType := tablet.Type
			if desiredType == topodatapb.TabletType_SPARE {
				desiredType = targetTabletType
			}

			// If starting queryservice fails, that's our new reason for being unhealthy.
			healthErr = agent.allowQueries(desiredType)
		}
	} else {
		if isServing {
			// We are not healthy or should not be running the query service.
			//
			// We do NOT enter lameduck in this case, because we should only hit this
			// in the following scenarios:
			//
			// * Healthcheck fails: We're probably serving errors anyway, so no point.
			// * Replication lag exceeds unhealthy threshold: This is very rare, so it
			//   isn't worth optimizing the potential 1s of errors away. It will also
			//   go away when vtgate is the only one looking at lag.
			// * We're in a special state where queryservice should be disabled
			//   despite being non-SPARE: This is not a live serving instance anyway.
			agent.disallowQueries(tablet.Type,
				fmt.Sprintf("health-check failure(%v)", healthErr),
			)
		}
	}

	// save the health record
	record := &HealthRecord{
		Error:            healthErr,
		ReplicationDelay: replicationDelay,
		Time:             time.Now(),
//.........这里部分代码省略.........

// changeCallback is run after every action that might
// have changed something in the tablet record or in the topology.
//
// It owns making changes to the BinlogPlayerMap. The input for this is the
// tablet type (has to be master), and the shard's SourceShards.
//
// It owns updating the blacklisted tables.
//
// It owns updating the stats record for 'TabletType'.
//
// It owns starting and stopping the update stream service.
//
// It owns reading the TabletControl for the current tablet, and storing it.
func (agent *ActionAgent) changeCallback(ctx context.Context, oldTablet, newTablet *topodatapb.Tablet) {
	span := trace.NewSpanFromContext(ctx)
	span.StartLocal("ActionAgent.changeCallback")
	defer span.Finish()

	allowQuery := topo.IsRunningQueryService(newTablet.Type)
	broadcastHealth := false
	runUpdateStream := allowQuery

	// Read the shard to get SourceShards / TabletControlMap if
	// we're going to use it.
	var shardInfo *topo.ShardInfo
	var err error
	var disallowQueryReason string
	var blacklistedTables []string
	updateBlacklistedTables := true
	if allowQuery {
		shardInfo, err = agent.TopoServer.GetShard(ctx, newTablet.Keyspace, newTablet.Shard)
		if err != nil {
			log.Errorf("Cannot read shard for this tablet %v, might have inaccurate SourceShards and TabletControls: %v", newTablet.Alias, err)
			updateBlacklistedTables = false
		} else {
			if newTablet.Type == topodatapb.TabletType_MASTER {
				if len(shardInfo.SourceShards) > 0 {
					allowQuery = false
					disallowQueryReason = "master tablet with filtered replication on"
				}
			}
			if tc := shardInfo.GetTabletControl(newTablet.Type); tc != nil {
				if topo.InCellList(newTablet.Alias.Cell, tc.Cells) {
					if tc.DisableQueryService {
						allowQuery = false
						disallowQueryReason = "TabletControl.DisableQueryService set"
					}
					blacklistedTables = tc.BlacklistedTables
				}
			}
		}
	} else {
		disallowQueryReason = fmt.Sprintf("not a serving tablet type(%v)", newTablet.Type)
	}
	agent.setServicesDesiredState(disallowQueryReason, runUpdateStream)
	if updateBlacklistedTables {
		if err := agent.loadBlacklistRules(newTablet, blacklistedTables); err != nil {
			// FIXME(alainjobart) how to handle this error?
			log.Errorf("Cannot update blacklisted tables rule: %v", err)
		} else {
			agent.setBlacklistedTables(blacklistedTables)
		}
	}

	if allowQuery {
		// Query service should be running.
		if oldTablet.Type == topodatapb.TabletType_REPLICA &&
			newTablet.Type == topodatapb.TabletType_MASTER {
			// When promoting from replica to master, allow both master and replica
			// queries to be served during gracePeriod.
			if _, err := agent.QueryServiceControl.SetServingType(newTablet.Type,
				true, []topodatapb.TabletType{oldTablet.Type}); err == nil {
				// If successful, broadcast to vtgate and then wait.
				agent.broadcastHealth()
				time.Sleep(*gracePeriod)
			} else {
				log.Errorf("Can't start query service for MASTER+REPLICA mode: %v", err)
			}
		}

		if stateChanged, err := agent.QueryServiceControl.SetServingType(newTablet.Type, true, nil); err == nil {
			// If the state changed, broadcast to vtgate.
			// (e.g. this happens when the tablet was already master, but it just
			// changed from NOT_SERVING to SERVING due to
			// "vtctl MigrateServedFrom ... master".)
			if stateChanged {
				broadcastHealth = true
			}
		} else {
			runUpdateStream = false
			log.Errorf("Cannot start query service: %v", err)
		}
	} else {
		// Query service should be stopped.
		if topo.IsSubjectToLameduck(oldTablet.Type) &&
			newTablet.Type == topodatapb.TabletType_SPARE &&
			*gracePeriod > 0 {
			// When a non-MASTER serving type is going SPARE,
			// put query service in lameduck during gracePeriod.
			agent.lameduck(disallowQueryReason)
//.........这里部分代码省略.........

// changeCallback is run after every action that might
// have changed something in the tablet record or in the topology.
func (agent *ActionAgent) changeCallback(ctx context.Context, oldTablet, newTablet *pbt.Tablet) error {
	span := trace.NewSpanFromContext(ctx)
	span.StartLocal("ActionAgent.changeCallback")
	defer span.Finish()

	allowQuery := topo.IsRunningQueryService(newTablet.Type)

	// Read the shard to get SourceShards / TabletControlMap if
	// we're going to use it.
	var shardInfo *topo.ShardInfo
	var tabletControl *pbt.Shard_TabletControl
	var blacklistedTables []string
	var err error
	var disallowQueryReason string
	if allowQuery {
		shardInfo, err = agent.TopoServer.GetShard(ctx, newTablet.Keyspace, newTablet.Shard)
		if err != nil {
			log.Errorf("Cannot read shard for this tablet %v, might have inaccurate SourceShards and TabletControls: %v", newTablet.Alias, err)
		} else {
			if newTablet.Type == pbt.TabletType_MASTER {
				if len(shardInfo.SourceShards) > 0 {
					allowQuery = false
					disallowQueryReason = "master tablet with filtered replication on"
				}
			}
			if tc := shardInfo.GetTabletControl(newTablet.Type); tc != nil {
				if topo.InCellList(newTablet.Alias.Cell, tc.Cells) {
					if tc.DisableQueryService {
						allowQuery = false
						disallowQueryReason = "query service disabled by tablet control"
					}
					blacklistedTables = tc.BlacklistedTables
					tabletControl = tc
				}
			}
		}
	} else {
		disallowQueryReason = fmt.Sprintf("not a serving tablet type(%v)", newTablet.Type)
	}

	if allowQuery {
		if err := agent.allowQueries(newTablet, blacklistedTables); err != nil {
			log.Errorf("Cannot start query service: %v", err)
		}
	} else {
		agent.disallowQueries(newTablet, disallowQueryReason)
	}

	// save the tabletControl we've been using, so the background
	// healthcheck makes the same decisions as we've been making.
	agent.setTabletControl(tabletControl)

	// update stream needs to be started or stopped too
	if topo.IsRunningUpdateStream(newTablet.Type) {
		agent.UpdateStream.Enable()
	} else {
		agent.UpdateStream.Disable()
	}

	statsType.Set(strings.ToLower(newTablet.Type.String()))
	statsKeyspace.Set(newTablet.Keyspace)
	statsShard.Set(newTablet.Shard)
	if newTablet.KeyRange != nil {
		statsKeyRangeStart.Set(hex.EncodeToString(newTablet.KeyRange.Start))
		statsKeyRangeEnd.Set(hex.EncodeToString(newTablet.KeyRange.End))
	} else {
		statsKeyRangeStart.Set("")
		statsKeyRangeEnd.Set("")
	}

	// See if we need to start or stop any binlog player
	if agent.BinlogPlayerMap != nil {
		if newTablet.Type == pbt.TabletType_MASTER {
			// Read the keyspace on masters to get
			// ShardingColumnType, for binlog replication,
			// only if source shards are set.
			var keyspaceInfo *topo.KeyspaceInfo
			if shardInfo != nil && len(shardInfo.SourceShards) > 0 {
				keyspaceInfo, err = agent.TopoServer.GetKeyspace(ctx, newTablet.Keyspace)
				if err != nil {
					keyspaceInfo = nil
				}
			}
			agent.BinlogPlayerMap.RefreshMap(agent.batchCtx, newTablet, keyspaceInfo, shardInfo)
		} else {
			agent.BinlogPlayerMap.StopAllPlayersAndReset()
		}
	}
	return nil
}

// changeCallback is run after every action that might
// have changed something in the tablet record or in the topology.
//
// It owns making changes to the BinlogPlayerMap. The input for this is the
// tablet type (has to be master), and the shard's SourceShards.
//
// It owns updating the blacklisted tables.
//
// It owns updating the stats record for 'TabletType'.
//
// It owns starting and stopping the update stream service.
//
// It owns reading the TabletControl for the current tablet, and storing it.
func (agent *ActionAgent) changeCallback(ctx context.Context, oldTablet, newTablet *topodatapb.Tablet) error {
	span := trace.NewSpanFromContext(ctx)
	span.StartLocal("ActionAgent.changeCallback")
	defer span.Finish()

	allowQuery := topo.IsRunningQueryService(newTablet.Type)

	// Read the shard to get SourceShards / TabletControlMap if
	// we're going to use it.
	var shardInfo *topo.ShardInfo
	var tabletControl *topodatapb.Shard_TabletControl
	var err error
	var disallowQueryReason string
	var blacklistedTables []string
	updateBlacklistedTables := true
	if allowQuery {
		shardInfo, err = agent.TopoServer.GetShard(ctx, newTablet.Keyspace, newTablet.Shard)
		if err != nil {
			log.Errorf("Cannot read shard for this tablet %v, might have inaccurate SourceShards and TabletControls: %v", newTablet.Alias, err)
			updateBlacklistedTables = false
		} else {
			if newTablet.Type == topodatapb.TabletType_MASTER {
				if len(shardInfo.SourceShards) > 0 {
					allowQuery = false
					disallowQueryReason = "master tablet with filtered replication on"
				}
			}
			if tc := shardInfo.GetTabletControl(newTablet.Type); tc != nil {
				if topo.InCellList(newTablet.Alias.Cell, tc.Cells) {
					if tc.DisableQueryService {
						allowQuery = false
						disallowQueryReason = "query service disabled by tablet control"
					}
					blacklistedTables = tc.BlacklistedTables
					tabletControl = tc
				}
			}
		}
	} else {
		disallowQueryReason = fmt.Sprintf("not a serving tablet type(%v)", newTablet.Type)
	}
	if updateBlacklistedTables {
		if err := agent.loadBlacklistRules(newTablet, blacklistedTables); err != nil {
			// FIXME(alainjobart) how to handle this error?
			log.Errorf("Cannot update blacklisted tables rule: %v", err)
		}
	}

	if allowQuery {
		// Query service should be running.
		if oldTablet.Type == topodatapb.TabletType_REPLICA &&
			newTablet.Type == topodatapb.TabletType_MASTER {
			// When promoting from replica to master, allow both master and replica
			// queries to be served during gracePeriod.
			if err := agent.QueryServiceControl.SetServingType(newTablet.Type, true,
				[]topodatapb.TabletType{oldTablet.Type}); err != nil {
				log.Errorf("Can't start query service for MASTER+REPLICA mode: %v", err)
			} else {
				// If successful, broadcast to vtgate and then wait.
				agent.broadcastHealth()
				time.Sleep(*gracePeriod)
			}
		}
		if err := agent.allowQueries(newTablet.Type); err != nil {
			log.Errorf("Cannot start query service: %v", err)
		}
	} else {
		// Query service should be stopped.
		if (oldTablet.Type == topodatapb.TabletType_REPLICA ||
			oldTablet.Type == topodatapb.TabletType_RDONLY) &&
			newTablet.Type == topodatapb.TabletType_SPARE {
			// When a non-MASTER serving type is going SPARE,
			// put query service in lameduck during gracePeriod.
			agent.enterLameduck(disallowQueryReason)
			agent.broadcastHealth()
			time.Sleep(*gracePeriod)
		}
		agent.disallowQueries(newTablet.Type, disallowQueryReason)
	}

	// save the tabletControl we've been using, so the background
	// healthcheck makes the same decisions as we've been making.
	agent.setTabletControl(tabletControl)

	// update stream needs to be started or stopped too
	if topo.IsRunningUpdateStream(newTablet.Type) {
		agent.UpdateStream.Enable()
//.........这里部分代码省略.........

// runHealthCheck takes the action mutex, runs the health check,
// and if we need to change our state, do it.
// If we are the master, we don't change our type, healthy or not.
// If we are not the master, we change to spare if not healthy,
// or to the passed in targetTabletType if healthy.
//
// Note we only update the topo record if we need to, that is if our type or
// health details changed.
func (agent *ActionAgent) runHealthCheck(targetTabletType topo.TabletType) {
	agent.actionMutex.Lock()
	defer agent.actionMutex.Unlock()

	// read the current tablet record and tablet control
	agent.mutex.Lock()
	tablet := agent._tablet
	tabletControl := agent._tabletControl
	agent.mutex.Unlock()

	// figure out if we should be running the query service
	shouldQueryServiceBeRunning := false
	var blacklistedTables []string
	if topo.IsRunningQueryService(targetTabletType) && agent.BinlogPlayerMap.size() == 0 {
		shouldQueryServiceBeRunning = true
		if tabletControl != nil {
			blacklistedTables = tabletControl.BlacklistedTables
			if tabletControl.DisableQueryService {
				shouldQueryServiceBeRunning = false
			}
		}
	}

	// run the health check
	typeForHealthCheck := targetTabletType
	if tablet.Type == topo.TYPE_MASTER {
		typeForHealthCheck = topo.TYPE_MASTER
	}
	replicationDelay, err := agent.HealthReporter.Report(topo.IsSlaveType(typeForHealthCheck), shouldQueryServiceBeRunning)
	health := make(map[string]string)
	if err == nil {
		if replicationDelay > *unhealthyThreshold {
			err = fmt.Errorf("reported replication lag: %v higher than unhealthy threshold: %v", replicationDelay.Seconds(), unhealthyThreshold.Seconds())
		} else if replicationDelay > *degradedThreshold {
			health[topo.ReplicationLag] = topo.ReplicationLagHigh
		}
	}

	// Figure out if we should be running QueryService, see if we are,
	// and reconcile.
	if err != nil {
		// we are not healthy, we should not be running QueryService
		shouldQueryServiceBeRunning = false
	}
	isQueryServiceRunning := agent.QueryServiceControl.IsServing()
	if shouldQueryServiceBeRunning {
		if !isQueryServiceRunning {
			// we remember this new possible error
			err = agent.allowQueries(tablet.Tablet, blacklistedTables)
		}
	} else {
		if isQueryServiceRunning {
			// we are not healthy or should not be running the
			// query service, shut it down.
			agent.disallowQueries()
		}
	}

	// save the health record
	record := &HealthRecord{
		Error:            err,
		ReplicationDelay: replicationDelay,
		Time:             time.Now(),
	}
	agent.History.Add(record)

	// try to figure out the mysql port if we don't have it yet
	if _, ok := tablet.Portmap["mysql"]; !ok {
		// we don't know the port, try to get it from mysqld
		mysqlPort, err := agent.MysqlDaemon.GetMysqlPort()
		if err != nil {
			// Don't log if we're already in a waiting-for-mysql state.
			agent.mutex.Lock()
			if !agent._waitingForMysql {
				log.Warningf("Can't get mysql port, won't populate Tablet record in topology (will retry silently at healthcheck interval %v): %v", *healthCheckInterval, err)
				agent._waitingForMysql = true
			}
			agent.mutex.Unlock()
		} else {
			log.Infof("Updating tablet mysql port to %v", mysqlPort)
			if err := agent.TopoServer.UpdateTabletFields(agent.batchCtx, tablet.Alias, func(tablet *topo.Tablet) error {
				tablet.Portmap["mysql"] = mysqlPort
				return nil
			}); err != nil {
				log.Infof("Error updating mysql port in tablet record: %v", err)
				return
			}

			// save the port so we don't update it again next time
			// we do the health check.
			agent.mutex.Lock()
			agent._tablet.Portmap["mysql"] = mysqlPort
//.........这里部分代码省略.........