func (bpc *BinlogPlayerController) Iteration() (err error) {
	defer func() {
		if x := recover(); x != nil {
			log.Errorf("%v: caught panic: %v", bpc, x)
			err = fmt.Errorf("panic: %v", x)
		}
	}()

	// Enable any user to set the timestamp.
	// We do it on every iteration to be sure, in case mysql was
	// restarted.
	bpc.DisableSuperToSetTimestamp()

	// create the db connection, connect it
	vtClient := binlogplayer.NewDbClient(bpc.dbConfig)
	if err := vtClient.Connect(); err != nil {
		return fmt.Errorf("can't connect to database: %v", err)
	}
	defer vtClient.Close()

	// Read the start position
	startPosition, err := binlogplayer.ReadStartPosition(vtClient, bpc.sourceShard.Uid)
	if err != nil {
		return fmt.Errorf("can't read startPosition: %v", err)
	}

	// Find the server list for the source shard in our cell
	addrs, err := bpc.ts.GetEndPoints(bpc.cell, bpc.sourceShard.Keyspace, bpc.sourceShard.Shard, topo.TYPE_REPLICA)
	if err != nil {
		return fmt.Errorf("can't find any source tablet for %v %v %v: %v", bpc.cell, bpc.sourceShard.String(), topo.TYPE_REPLICA, err)
	}
	if len(addrs.Entries) == 0 {
		return fmt.Errorf("empty source tablet list for %v %v %v", bpc.cell, bpc.sourceShard.String(), topo.TYPE_REPLICA)
	}
	newServerIndex := rand.Intn(len(addrs.Entries))
	addr := fmt.Sprintf("%v:%v", addrs.Entries[newServerIndex].Host, addrs.Entries[newServerIndex].NamedPortMap["_vtocc"])

	// check which kind of replication we're doing, tables or keyrange
	if len(bpc.sourceShard.Tables) > 0 {
		// tables, just get them
		player := binlogplayer.NewBinlogPlayerTables(vtClient, addr, bpc.sourceShard.Tables, startPosition, bpc.stopAtGroupId)
		return player.ApplyBinlogEvents(bpc.interrupted)
	} else {
		// the data we have to replicate is the intersection of the
		// source keyrange and our keyrange
		overlap, err := key.KeyRangesOverlap(bpc.sourceShard.KeyRange, bpc.keyRange)
		if err != nil {
			return fmt.Errorf("Source shard %v doesn't overlap destination shard %v", bpc.sourceShard.KeyRange, bpc.keyRange)
		}

		player := binlogplayer.NewBinlogPlayerKeyRange(vtClient, addr, overlap, startPosition, bpc.stopAtGroupId)
		return player.ApplyBinlogEvents(bpc.interrupted)
	}
}

// BlpPositionList returns the current position of all the players.
func (blm *BinlogPlayerMap) BlpPositionList() (*blproto.BlpPositionList, error) {
	// create a db connection for this purpose
	vtClient := binlogplayer.NewDbClient(blm.dbConfig)
	if err := vtClient.Connect(); err != nil {
		return nil, fmt.Errorf("can't connect to database: %v", err)
	}
	defer vtClient.Close()

	result := &blproto.BlpPositionList{}
	blm.mu.Lock()
	defer blm.mu.Unlock()
	for _, bpc := range blm.players {
		blp, _, err := bpc.BlpPosition(vtClient)
		if err != nil {
			return nil, fmt.Errorf("can't read current position for %v: %v", bpc, err)
		}

		result.Entries = append(result.Entries, *blp)
	}
	return result, nil
}

// NewActionAgent creates a new ActionAgent and registers all the
// associated services.
//
// batchCtx is the context that the agent will use for any background tasks
// it spawns.
func NewActionAgent(
	batchCtx context.Context,
	mysqld mysqlctl.MysqlDaemon,
	queryServiceControl tabletserver.Controller,
	tabletAlias *topodatapb.TabletAlias,
	dbcfgs dbconfigs.DBConfigs,
	mycnf *mysqlctl.Mycnf,
	port, gRPCPort int32,
	overridesFile string,
) (agent *ActionAgent, err error) {
	schemaOverrides := loadSchemaOverrides(overridesFile)

	topoServer := topo.GetServer()

	agent = &ActionAgent{
		QueryServiceControl: queryServiceControl,
		HealthReporter:      health.DefaultAggregator,
		batchCtx:            batchCtx,
		TopoServer:          topoServer,
		TabletAlias:         tabletAlias,
		MysqlDaemon:         mysqld,
		DBConfigs:           dbcfgs,
		SchemaOverrides:     schemaOverrides,
		History:             history.New(historyLength),
		lastHealthMapCount:  stats.NewInt("LastHealthMapCount"),
		_healthy:            fmt.Errorf("healthcheck not run yet"),
	}
	agent.registerQueryRuleSources()

	// try to initialize the tablet if we have to
	if err := agent.InitTablet(port, gRPCPort); err != nil {
		return nil, fmt.Errorf("agent.InitTablet failed: %v", err)
	}

	// Publish and set the TargetTabletType. Not a global var
	// since it should never be changed.
	statsTabletType := stats.NewString("TargetTabletType")
	statsTabletType.Set(*targetTabletType)

	// Create the TabletType stats
	agent.exportStats = true
	agent.statsTabletType = stats.NewString("TabletType")

	// Start the binlog player services, not playing at start.
	agent.BinlogPlayerMap = NewBinlogPlayerMap(topoServer, mysqld, func() binlogplayer.VtClient {
		return binlogplayer.NewDbClient(&agent.DBConfigs.Filtered)
	})
	// Stop all binlog players upon entering lameduck.
	servenv.OnTerm(agent.BinlogPlayerMap.StopAllPlayersAndReset)
	RegisterBinlogPlayerMap(agent.BinlogPlayerMap)

	// try to figure out the mysql port
	mysqlPort := mycnf.MysqlPort
	if mysqlPort == 0 {
		// we don't know the port, try to get it from mysqld
		var err error
		mysqlPort, err = mysqld.GetMysqlPort()
		if err != nil {
			log.Warningf("Cannot get current mysql port, will use 0 for now: %v", err)
		}
	}

	// Start will get the tablet info, and update our state from it
	if err := agent.Start(batchCtx, int32(mysqlPort), port, gRPCPort, true); err != nil {
		return nil, err
	}

	// register the RPC services from the agent
	agent.registerQueryService()

	// two cases then:
	// - restoreFromBackup is set: we restore, then initHealthCheck, all
	//   in the background
	// - restoreFromBackup is not set: we initHealthCheck right away
	if *restoreFromBackup {
		go func() {
			// restoreFromBackup wil just be a regular action
			// (same as if it was triggered remotely)
			if err := agent.RestoreFromBackup(batchCtx); err != nil {
				println(fmt.Sprintf("RestoreFromBackup failed: %v", err))
				log.Fatalf("RestoreFromBackup failed: %v", err)
			}

			// after the restore is done, start health check
			agent.initHealthCheck()
		}()
	} else {
		// synchronously start health check if needed
		agent.initHealthCheck()
	}

	return agent, nil
}

// Iteration is a single iteration for the player: get the current status,
// try to play, and plays until interrupted, or until an error occurs.
func (bpc *BinlogPlayerController) Iteration() (err error) {
	defer func() {
		if x := recover(); x != nil {
			log.Errorf("%v: caught panic: %v", bpc, x)
			err = fmt.Errorf("panic: %v", x)
		}
	}()

	// Apply any special settings necessary for playback of binlogs.
	// We do it on every iteration to be sure, in case MySQL was restarted.
	if err := bpc.mysqld.EnableBinlogPlayback(); err != nil {
		// We failed to apply the required settings, so we shouldn't keep going.
		return err
	}

	// create the db connection, connect it
	vtClient := binlogplayer.NewDbClient(bpc.dbConfig)
	if err := vtClient.Connect(); err != nil {
		return fmt.Errorf("can't connect to database: %v", err)
	}
	defer vtClient.Close()

	// Read the start position
	startPosition, flags, err := binlogplayer.ReadStartPosition(vtClient, bpc.sourceShard.Uid)
	if err != nil {
		return fmt.Errorf("can't read startPosition: %v", err)
	}

	// if we shouldn't start, we just error out and try again later
	if strings.Index(flags, binlogplayer.BlpFlagDontStart) != -1 {
		return fmt.Errorf("not starting because flag '%v' is set", binlogplayer.BlpFlagDontStart)
	}

	// Find the server list for the source shard in our cell
	addrs, _, err := bpc.ts.GetEndPoints(bpc.ctx, bpc.cell, bpc.sourceShard.Keyspace, bpc.sourceShard.Shard, topo.TYPE_REPLICA)
	if err != nil {
		// If this calls fails because the context was canceled,
		// we need to return nil.
		select {
		case <-bpc.ctx.Done():
			if bpc.ctx.Err() == context.Canceled {
				return nil
			}
		default:
		}
		return fmt.Errorf("can't find any source tablet for %v %v %v: %v", bpc.cell, bpc.sourceShard.String(), topo.TYPE_REPLICA, err)
	}
	if len(addrs.Entries) == 0 {
		return fmt.Errorf("empty source tablet list for %v %v %v", bpc.cell, bpc.sourceShard.String(), topo.TYPE_REPLICA)
	}
	newServerIndex := rand.Intn(len(addrs.Entries))
	endPoint := addrs.Entries[newServerIndex]

	// save our current server
	bpc.playerMutex.Lock()
	bpc.sourceTablet = topo.TabletAlias{
		Cell: bpc.cell,
		Uid:  addrs.Entries[newServerIndex].Uid,
	}
	bpc.lastError = nil
	bpc.playerMutex.Unlock()

	// check which kind of replication we're doing, tables or keyrange
	if len(bpc.sourceShard.Tables) > 0 {
		// tables, first resolve wildcards
		tables, err := mysqlctl.ResolveTables(bpc.mysqld, bpc.dbName, bpc.sourceShard.Tables)
		if err != nil {
			return fmt.Errorf("failed to resolve table names: %v", err)
		}

		// tables, just get them
		player := binlogplayer.NewBinlogPlayerTables(vtClient, endPoint, tables, startPosition, bpc.stopPosition, bpc.binlogPlayerStats)
		return player.ApplyBinlogEvents(bpc.ctx)
	}
	// the data we have to replicate is the intersection of the
	// source keyrange and our keyrange
	overlap, err := key.KeyRangesOverlap3(bpc.sourceShard.KeyRange, bpc.keyRange)
	if err != nil {
		return fmt.Errorf("Source shard %v doesn't overlap destination shard %v", bpc.sourceShard.KeyRange, bpc.keyRange)
	}

	player := binlogplayer.NewBinlogPlayerKeyRange(vtClient, endPoint, bpc.keyspaceIDType, overlap, startPosition, bpc.stopPosition, bpc.binlogPlayerStats)
	return player.ApplyBinlogEvents(bpc.ctx)
}

// NewActionAgent creates a new ActionAgent and registers all the
// associated services.
//
// batchCtx is the context that the agent will use for any background tasks
// it spawns.
func NewActionAgent(
	batchCtx context.Context,
	mysqld mysqlctl.MysqlDaemon,
	queryServiceControl tabletserver.Controller,
	tabletAlias *topodatapb.TabletAlias,
	dbcfgs dbconfigs.DBConfigs,
	mycnf *mysqlctl.Mycnf,
	port, gRPCPort int32,
) (agent *ActionAgent, err error) {
	topoServer := topo.GetServer()

	orc, err := newOrcClient()
	if err != nil {
		return nil, err
	}

	agent = &ActionAgent{
		QueryServiceControl: queryServiceControl,
		HealthReporter:      health.DefaultAggregator,
		batchCtx:            batchCtx,
		TopoServer:          topoServer,
		TabletAlias:         tabletAlias,
		MysqlDaemon:         mysqld,
		DBConfigs:           dbcfgs,
		History:             history.New(historyLength),
		_healthy:            fmt.Errorf("healthcheck not run yet"),
		orc:                 orc,
	}
	agent.registerQueryRuleSources()

	// try to initialize the tablet if we have to
	if err := agent.InitTablet(port, gRPCPort); err != nil {
		return nil, fmt.Errorf("agent.InitTablet failed: %v", err)
	}

	// Create the TabletType stats
	agent.exportStats = true
	agent.statsTabletType = stats.NewString("TabletType")

	// Start the binlog player services, not playing at start.
	agent.BinlogPlayerMap = NewBinlogPlayerMap(topoServer, mysqld, func() binlogplayer.VtClient {
		return binlogplayer.NewDbClient(&agent.DBConfigs.Filtered)
	})
	// Stop all binlog players upon entering lameduck.
	servenv.OnTerm(agent.BinlogPlayerMap.StopAllPlayersAndReset)
	RegisterBinlogPlayerMap(agent.BinlogPlayerMap)

	// try to figure out the mysql port
	mysqlPort := mycnf.MysqlPort
	if mysqlPort == 0 {
		// we don't know the port, try to get it from mysqld
		var err error
		mysqlPort, err = mysqld.GetMysqlPort()
		if err != nil {
			log.Warningf("Cannot get current mysql port, will use 0 for now: %v", err)
		}
	}

	// Start will get the tablet info, and update our state from it
	if err := agent.Start(batchCtx, int32(mysqlPort), port, gRPCPort, true); err != nil {
		return nil, err
	}

	// register the RPC services from the agent
	servenv.OnRun(func() {
		agent.registerQueryService()
	})

	// two cases then:
	// - restoreFromBackup is set: we restore, then initHealthCheck, all
	//   in the background
	// - restoreFromBackup is not set: we initHealthCheck right away
	if *restoreFromBackup {
		go func() {
			// restoreFromBackup wil just be a regular action
			// (same as if it was triggered remotely)
			if err := agent.RestoreData(batchCtx, logutil.NewConsoleLogger(), false /* deleteBeforeRestore */); err != nil {
				println(fmt.Sprintf("RestoreFromBackup failed: %v", err))
				log.Fatalf("RestoreFromBackup failed: %v", err)
			}

			// after the restore is done, start health check
			agent.initHealthCheck()
		}()
	} else {
		// update our state
		if err := agent.refreshTablet(batchCtx, "Start"); err != nil {
			return nil, err
		}

		// synchronously start health check if needed
		agent.initHealthCheck()
	}

	// Start periodic Orchestrator self-registration, if configured.
//.........这里部分代码省略.........

// Iteration is a single iteration for the player: get the current status,
// try to play, and plays until interrupted, or until an error occurs.
func (bpc *BinlogPlayerController) Iteration() (err error) {
	defer func() {
		if x := recover(); x != nil {
			log.Errorf("%v: caught panic: %v", bpc, x)
			err = fmt.Errorf("panic: %v", x)
		}
	}()

	// Enable any user to set the timestamp.
	// We do it on every iteration to be sure, in case mysql was
	// restarted.
	bpc.DisableSuperToSetTimestamp()

	// create the db connection, connect it
	vtClient := binlogplayer.NewDbClient(bpc.dbConfig)
	if err := vtClient.Connect(); err != nil {
		return fmt.Errorf("can't connect to database: %v", err)
	}
	defer vtClient.Close()

	// Read the start position
	startPosition, flags, err := binlogplayer.ReadStartPosition(vtClient, bpc.sourceShard.Uid)
	if err != nil {
		return fmt.Errorf("can't read startPosition: %v", err)
	}

	// if we shouldn't start, we just error out and try again later
	if strings.Index(flags, binlogplayer.BLP_FLAG_DONT_START) != -1 {
		return fmt.Errorf("not starting because flag '%v' is set", binlogplayer.BLP_FLAG_DONT_START)
	}

	// Find the server list for the source shard in our cell
	addrs, err := bpc.ts.GetEndPoints(bpc.cell, bpc.sourceShard.Keyspace, bpc.sourceShard.Shard, topo.TYPE_REPLICA)
	if err != nil {
		return fmt.Errorf("can't find any source tablet for %v %v %v: %v", bpc.cell, bpc.sourceShard.String(), topo.TYPE_REPLICA, err)
	}
	if len(addrs.Entries) == 0 {
		return fmt.Errorf("empty source tablet list for %v %v %v", bpc.cell, bpc.sourceShard.String(), topo.TYPE_REPLICA)
	}
	newServerIndex := rand.Intn(len(addrs.Entries))
	addr := fmt.Sprintf("%v:%v", addrs.Entries[newServerIndex].Host, addrs.Entries[newServerIndex].NamedPortMap["_vtocc"])

	// save our current server
	bpc.playerMutex.Lock()
	bpc.sourceTablet = topo.TabletAlias{
		Cell: bpc.cell,
		Uid:  addrs.Entries[newServerIndex].Uid,
	}
	bpc.lastError = nil
	bpc.playerMutex.Unlock()

	// check which kind of replication we're doing, tables or keyrange
	if len(bpc.sourceShard.Tables) > 0 {
		// tables, first resolve wildcards
		tables, err := bpc.mysqld.ResolveTables(bpc.dbName, bpc.sourceShard.Tables)
		if err != nil {
			return fmt.Errorf("failed to resolve table names: %v", err)
		}

		// tables, just get them
		player := binlogplayer.NewBinlogPlayerTables(vtClient, addr, tables, startPosition, bpc.stopAtGTID, bpc.binlogPlayerStats)
		return player.ApplyBinlogEvents(bpc.interrupted)
	} else {
		// the data we have to replicate is the intersection of the
		// source keyrange and our keyrange
		overlap, err := key.KeyRangesOverlap(bpc.sourceShard.KeyRange, bpc.keyRange)
		if err != nil {
			return fmt.Errorf("Source shard %v doesn't overlap destination shard %v", bpc.sourceShard.KeyRange, bpc.keyRange)
		}

		player := binlogplayer.NewBinlogPlayerKeyRange(vtClient, addr, bpc.keyspaceIdType, overlap, startPosition, bpc.stopAtGTID, bpc.binlogPlayerStats)
		return player.ApplyBinlogEvents(bpc.interrupted)
	}
}