func (agent *ActionAgent) initHealthCheck() {
	if !agent.IsRunningHealthCheck() {
		log.Infof("No target_tablet_type specified, disabling any health check")
		return
	}

	tt, err := topoproto.ParseTabletType(*targetTabletType)
	if err != nil {
		log.Fatalf("Invalid target tablet type %v: %v", *targetTabletType, err)
	}

	log.Infof("Starting periodic health check every %v with target_tablet_type=%v", *healthCheckInterval, *targetTabletType)
	t := timer.NewTimer(*healthCheckInterval)
	servenv.OnTermSync(func() {
		// When we enter lameduck mode, we want to not call
		// the health check any more. After this returns, we
		// are guaranteed to not call it.
		log.Info("Stopping periodic health check timer")
		t.Stop()

		// Now we can finish up and force ourselves to not healthy.
		agent.terminateHealthChecks(tt)
	})
	t.Start(func() {
		agent.runHealthCheck(tt)
	})
	t.Trigger()
}

func main() {
	defer exit.Recover()

	flag.Parse()
	servenv.Init()

	ts := topo.GetServer()
	defer topo.CloseServers()

	resilientSrvTopoServer = vtgate.NewResilientSrvTopoServer(ts, "ResilientSrvTopoServer")

	healthCheck = discovery.NewHealthCheck(*healthCheckConnTimeout, *healthCheckRetryDelay, *healthCheckTimeout)
	healthCheck.RegisterStats()

	tabletTypes := make([]topodatapb.TabletType, 0, 1)
	if len(*tabletTypesToWait) != 0 {
		for _, ttStr := range strings.Split(*tabletTypesToWait, ",") {
			tt, err := topoproto.ParseTabletType(ttStr)
			if err != nil {
				log.Errorf("unknown tablet type: %v", ttStr)
				continue
			}
			tabletTypes = append(tabletTypes, tt)
		}
	}
	l2vtg := l2vtgate.Init(healthCheck, ts, resilientSrvTopoServer, *cell, *retryCount, tabletTypes)

	servenv.OnRun(func() {
		addStatusParts(l2vtg)
	})
	servenv.RunDefault()
}

// TabletTypeToProto turns a TabletType into a proto
func TabletTypeToProto(t TabletType) pb.TabletType {
	if result, err := topoproto.ParseTabletType(string(t)); err != nil {
		panic(fmt.Errorf("unknown tablet type: %v", t))
	} else {
		return result
	}
}

func main() {
	defer exit.Recover()

	flag.Parse()
	servenv.Init()

	if initFakeZK != nil {
		initFakeZK()
	}
	ts := topo.GetServer()
	defer topo.CloseServers()

	resilientSrvTopoServer = vtgate.NewResilientSrvTopoServer(ts, "ResilientSrvTopoServer")

	healthCheck = discovery.NewHealthCheck(*connTimeoutTotal, *healthCheckRetryDelay, *healthCheckTimeout, "" /* statsSuffix */)

	tabletTypes := make([]topodatapb.TabletType, 0, 1)
	if len(*tabletTypesToWait) != 0 {
		for _, ttStr := range strings.Split(*tabletTypesToWait, ",") {
			tt, err := topoproto.ParseTabletType(ttStr)
			if err != nil {
				log.Errorf("unknown tablet type: %v", ttStr)
				continue
			}
			tabletTypes = append(tabletTypes, tt)
		}
	}
	vtg := vtgate.Init(context.Background(), healthCheck, ts, resilientSrvTopoServer, *cell, *retryDelay, *retryCount, *connTimeoutTotal, *connTimeoutPerConn, *connLife, tabletTypes, *maxInFlight, *testGateway)

	servenv.OnRun(func() {
		addStatusParts(vtg)
	})
	servenv.RunDefault()
}

// tabletTypesLocked returns the tablet types needed to be displayed in the heatmap based on the dropdown filters.
// It returns tablet type if a specific one was chosen or returns all of them if 'all' is chosen for keyspace and/or cell.
// This method is used by heatmapData to traverse over the desired tablet types.
func (c *tabletStatsCache) tabletTypesLocked(keyspace, cell, tabletType string) []topodata.TabletType {
	if tabletType != "all" {
		tabletTypeObj, _ := topoproto.ParseTabletType(tabletType)
		return []topodata.TabletType{tabletTypeObj}
	}
	return c.typesInTopology(keyspace, cell)
}

func main() {
	defer exit.Recover()

	flag.Parse()
	servenv.Init()

	if initFakeZK != nil {
		initFakeZK()
	}
	ts := topo.GetServer()
	defer topo.CloseServers()

	var schema *planbuilder.Schema
	if *schemaFile != "" {
		var err error
		if schema, err = planbuilder.LoadFile(*schemaFile); err != nil {
			log.Error(err)
			exit.Return(1)
		}
		log.Infof("v3 is enabled: loaded schema from file: %v", *schemaFile)
	} else {
		ctx := context.Background()
		schemaJSON, err := ts.GetVSchema(ctx)
		if err != nil {
			log.Warningf("Skipping v3 initialization: GetVSchema failed: %v", err)
			goto startServer
		}
		schema, err = planbuilder.NewSchema([]byte(schemaJSON))
		if err != nil {
			log.Warningf("Skipping v3 initialization: GetVSchema failed: %v", err)
			goto startServer
		}
		log.Infof("v3 is enabled: loaded schema from topo")
	}

startServer:
	resilientSrvTopoServer = vtgate.NewResilientSrvTopoServer(ts, "ResilientSrvTopoServer")

	healthCheck = discovery.NewHealthCheck(*connTimeoutTotal, *healthCheckRetryDelay, *healthCheckTimeout, "" /* statsSuffix */)

	tabletTypes := make([]topodatapb.TabletType, 0, 1)
	if len(*tabletTypesToWait) != 0 {
		for _, ttStr := range strings.Split(*tabletTypesToWait, ",") {
			tt, err := topoproto.ParseTabletType(ttStr)
			if err != nil {
				log.Errorf("unknown tablet type: %v", ttStr)
				continue
			}
			tabletTypes = append(tabletTypes, tt)
		}
	}
	vtg := vtgate.Init(healthCheck, ts, resilientSrvTopoServer, schema, *cell, *retryDelay, *retryCount, *connTimeoutTotal, *connTimeoutPerConn, *connLife, tabletTypes, *maxInFlight, *testGateway)

	servenv.OnRun(func() {
		addStatusParts(vtg)
	})
	servenv.RunDefault()
}

// handleExplorerRedirect returns the redirect target URL.
func handleExplorerRedirect(r *http.Request) (string, error) {
	keyspace := r.FormValue("keyspace")
	shard := r.FormValue("shard")
	cell := r.FormValue("cell")

	switch r.FormValue("type") {
	case "keyspace":
		if keyspace == "" {
			return "", errors.New("keyspace is required for this redirect")
		}
		return explorer.GetKeyspacePath(keyspace), nil
	case "shard":
		if keyspace == "" || shard == "" {
			return "", errors.New("keyspace and shard are required for this redirect")
		}
		return explorer.GetShardPath(keyspace, shard), nil
	case "srv_keyspace":
		if keyspace == "" || cell == "" {
			return "", errors.New("keyspace and cell are required for this redirect")
		}
		return explorer.GetSrvKeyspacePath(cell, keyspace), nil
	case "srv_shard":
		if keyspace == "" || shard == "" || cell == "" {
			return "", errors.New("keyspace, shard, and cell are required for this redirect")
		}
		return explorer.GetSrvShardPath(cell, keyspace, shard), nil
	case "srv_type":
		tabletType := r.FormValue("tablet_type")
		if keyspace == "" || shard == "" || cell == "" || tabletType == "" {
			return "", errors.New("keyspace, shard, cell, and tablet_type are required for this redirect")
		}
		tt, err := topoproto.ParseTabletType(tabletType)
		if err != nil {
			return "", fmt.Errorf("cannot parse tablet type %v: %v", tabletType, err)
		}
		return explorer.GetSrvTypePath(cell, keyspace, shard, tt), nil
	case "tablet":
		alias := r.FormValue("alias")
		if alias == "" {
			return "", errors.New("alias is required for this redirect")
		}
		tabletAlias, err := topoproto.ParseTabletAlias(alias)
		if err != nil {
			return "", fmt.Errorf("bad tablet alias %q: %v", alias, err)
		}
		return explorer.GetTabletPath(tabletAlias), nil
	case "replication":
		if keyspace == "" || shard == "" || cell == "" {
			return "", errors.New("keyspace, shard, and cell are required for this redirect")
		}
		return explorer.GetReplicationSlaves(cell, keyspace, shard), nil
	default:
		return "", errors.New("bad redirect type")
	}
}

func commandVtTabletExecute(ctx context.Context, wr *wrangler.Wrangler, subFlags *flag.FlagSet, args []string) error {
	transactionID := subFlags.Int("transaction_id", 0, "transaction id to use, if inside a transaction.")
	bindVariables := newBindvars(subFlags)
	keyspace := subFlags.String("keyspace", "", "keyspace the tablet belongs to")
	shard := subFlags.String("shard", "", "shard the tablet belongs to")
	tabletType := subFlags.String("tablet_type", "unknown", "tablet type we expect from the tablet (use unknown to use sessionId)")
	connectTimeout := subFlags.Duration("connect_timeout", 30*time.Second, "Connection timeout for vttablet client")
	json := subFlags.Bool("json", false, "Output JSON instead of human-readable table")

	if err := subFlags.Parse(args); err != nil {
		return err
	}
	if subFlags.NArg() != 2 {
		return fmt.Errorf("the <tablet_alias> and <sql> arguments are required for the VtTabletExecute command")
	}
	tt, err := topoproto.ParseTabletType(*tabletType)
	if err != nil {
		return err
	}
	tabletAlias, err := topoproto.ParseTabletAlias(subFlags.Arg(0))
	if err != nil {
		return err
	}
	tabletInfo, err := wr.TopoServer().GetTablet(ctx, tabletAlias)
	if err != nil {
		return err
	}
	ep, err := topo.TabletEndPoint(tabletInfo.Tablet)
	if err != nil {
		return fmt.Errorf("cannot get EndPoint from tablet record: %v", err)
	}

	conn, err := tabletconn.GetDialer()(ctx, ep, *keyspace, *shard, tt, *connectTimeout)
	if err != nil {
		return fmt.Errorf("cannot connect to tablet %v: %v", tabletAlias, err)
	}
	defer conn.Close()

	qr, err := conn.Execute(ctx, subFlags.Arg(1), *bindVariables, int64(*transactionID))
	if err != nil {
		return fmt.Errorf("Execute failed: %v", err)
	}
	if *json {
		return printJSON(wr.Logger(), qr)
	}
	printQueryResult(loggerWriter{wr.Logger()}, qr)
	return nil
}

// Open must be called with a JSON string that looks like this:
// {"protocol": "gorpc", "address": "localhost:1111", "tablet_type": "master", "timeout": 1000000000}
// protocol specifies the rpc protocol to use.
// address specifies the address for the VTGate to connect to.
// tablet_type represents the consistency level of your operations.
// For example "replica" means eventually consistent reads, while
// "master" supports transactions and gives you read-after-write consistency.
// timeout is specified in nanoseconds. It applies for all operations.
func (d drv) Open(name string) (driver.Conn, error) {
	c := &conn{TabletType: "master"}
	err := json.Unmarshal([]byte(name), c)
	if err != nil {
		return nil, err
	}
	c.tabletType, err = topoproto.ParseTabletType(c.TabletType)
	if err != nil {
		return nil, err
	}
	err = c.dial()
	if err != nil {
		return nil, err
	}
	return c, nil
}

func (agent *ActionAgent) isMasterEligible() (bool, error) {
	switch agent.Tablet().Type {
	case topodatapb.TabletType_MASTER, topodatapb.TabletType_REPLICA:
		return true, nil
	case topodatapb.TabletType_SPARE:
		// If we're SPARE, it could be because healthcheck is enabled.
		tt, err := topoproto.ParseTabletType(*targetTabletType)
		if err != nil {
			return false, fmt.Errorf("can't determine if tablet is master-eligible: currently SPARE and no -target_tablet_type flag specified")
		}
		if tt == topodatapb.TabletType_REPLICA {
			return true, nil
		}
	}

	return false, nil
}

func commandVtTabletBegin(ctx context.Context, wr *wrangler.Wrangler, subFlags *flag.FlagSet, args []string) error {
	keyspace := subFlags.String("keyspace", "", "keyspace the tablet belongs to")
	shard := subFlags.String("shard", "", "shard the tablet belongs to")
	tabletType := subFlags.String("tablet_type", "unknown", "tablet type we expect from the tablet (use unknown to use sessionId)")
	connectTimeout := subFlags.Duration("connect_timeout", 30*time.Second, "Connection timeout for vttablet client")
	if err := subFlags.Parse(args); err != nil {
		return err
	}
	if subFlags.NArg() != 1 {
		return fmt.Errorf("the <tablet_alias> argument is required for the VtTabletBegin command")
	}
	tt, err := topoproto.ParseTabletType(*tabletType)
	if err != nil {
		return err
	}
	tabletAlias, err := topoproto.ParseTabletAlias(subFlags.Arg(0))
	if err != nil {
		return err
	}
	tabletInfo, err := wr.TopoServer().GetTablet(ctx, tabletAlias)
	if err != nil {
		return err
	}
	ep, err := topo.TabletEndPoint(tabletInfo.Tablet)
	if err != nil {
		return fmt.Errorf("cannot get EndPoint from tablet record: %v", err)
	}

	conn, err := tabletconn.GetDialer()(ctx, ep, *keyspace, *shard, tt, *connectTimeout)
	if err != nil {
		return fmt.Errorf("cannot connect to tablet %v: %v", tabletAlias, err)
	}
	defer conn.Close()

	transactionID, err := conn.Begin(ctx)
	if err != nil {
		return fmt.Errorf("Begin failed: %v", err)
	}
	result := map[string]int64{
		"transaction_id": transactionID,
	}
	return printJSON(wr, result)
}

// GetSrvTabletTypesPerShard is part of the topo.Server interface
func (zkts *Server) GetSrvTabletTypesPerShard(ctx context.Context, cell, keyspace, shard string) ([]topodatapb.TabletType, error) {
	zkSgShardPath := zkPathForVtShard(cell, keyspace, shard)
	children, _, err := zkts.zconn.Children(zkSgShardPath)
	if err != nil {
		if zookeeper.IsError(err, zookeeper.ZNONODE) {
			err = topo.ErrNoNode
		}
		return nil, err
	}
	result := make([]topodatapb.TabletType, 0, len(children))
	for _, tt := range children {
		// these two are used for locking
		if tt == "action" || tt == "actionlog" {
			continue
		}
		if ptt, err := topoproto.ParseTabletType(tt); err == nil {
			result = append(result, ptt)
		}
	}
	return result, nil
}

// Open implements the database/sql/driver.Driver interface.
//
// For "name", the Vitess driver requires that a JSON object is passed in.
//
// Instead of using this call and passing in a hand-crafted JSON string, it's
// recommended to use the public Vitess helper functions like
// Open(), OpenShard() or OpenWithConfiguration() instead. These will generate
// the required JSON string behind the scenes for you.
//
// Example for a JSON string:
//
//   {"protocol": "grpc", "address": "localhost:1111", "tablet_type": "master", "timeout": 1000000000}
//
// For a description of the available fields, see the Configuration struct.
// Note: In the JSON string, timeout has to be specified in nanoseconds.
func (d drv) Open(name string) (driver.Conn, error) {
	c := &conn{Configuration: newDefaultConfiguration()}
	err := json.Unmarshal([]byte(name), c)
	if err != nil {
		return nil, err
	}
	if c.Keyspace == "" && c.Shard != "" {
		return nil, fmt.Errorf("the shard parameter requires a keyspace parameter. shard: %v", c.Shard)
	}
	if c.useExecuteShards() {
		log.Infof("Sending queries only to keyspace/shard: %v/%v", c.Keyspace, c.Shard)
	}
	c.tabletTypeProto, err = topoproto.ParseTabletType(c.TabletType)
	if err != nil {
		return nil, err
	}
	err = c.dial()
	if err != nil {
		return nil, err
	}
	return c, nil
}

// Open implements the database/sql/driver.Driver interface.
//
// For "name", the Vitess driver requires that a JSON object is passed in.
//
// Instead of using this call and passing in a hand-crafted JSON string, it's
// recommended to use the public Vitess helper functions like
// Open(), OpenShard() or OpenWithConfiguration() instead. These will generate
// the required JSON string behind the scenes for you.
//
// Example for a JSON string:
//
//   {"protocol": "gorpc", "address": "localhost:1111", "tablet_type": "master", "timeout": 1000000000}
//
// For a description of the available fields, see the Configuration struct.
// Note: In the JSON string, timeout has to be specified in nanoseconds.
func (d drv) Open(name string) (driver.Conn, error) {
	c := &conn{Configuration: newDefaultConfiguration()}
	err := json.Unmarshal([]byte(name), c)
	if err != nil {
		return nil, err
	}
	if (c.Keyspace != "" && c.Shard == "") || (c.Keyspace == "" && c.Shard != "") {
		return nil, fmt.Errorf("Always set both keyspace and shard or leave both empty. keyspace: %v shard: %v", c.Keyspace, c.Shard)
	}
	if c.useExecuteShards() {
		log.Infof("Sending queries only to keyspace/shard: %v/%v", c.Keyspace, c.Shard)
	}
	c.tabletTypeProto, err = topoproto.ParseTabletType(c.TabletType)
	if err != nil {
		return nil, err
	}
	err = c.dial()
	if err != nil {
		return nil, err
	}
	return c, nil
}

// GetSrvTabletTypesPerShard implements topo.Server.
func (s *Server) GetSrvTabletTypesPerShard(ctx context.Context, cellName, keyspace, shard string) ([]topodatapb.TabletType, error) {
	cell, err := s.getCell(cellName)
	if err != nil {
		return nil, err
	}

	resp, err := cell.Get(srvShardDirPath(keyspace, shard), false /* sort */, false /* recursive */)
	if err != nil {
		return nil, convertError(err)
	}
	if resp.Node == nil {
		return nil, ErrBadResponse
	}

	tabletTypes := make([]topodatapb.TabletType, 0, len(resp.Node.Nodes))
	for _, n := range resp.Node.Nodes {
		strType := path.Base(n.Key)
		if tt, err := topoproto.ParseTabletType(strType); err == nil {
			tabletTypes = append(tabletTypes, tt)
		}
	}
	return tabletTypes, nil
}

// InitTablet initializes the tablet record if necessary.
func (agent *ActionAgent) InitTablet(port, gRPCPort int32) error {
	// only enabled if one of init_tablet_type (when healthcheck
	// is disabled) or init_keyspace (when healthcheck is enabled)
	// is passed in, then check other parameters
	if *initTabletType == "" && *initKeyspace == "" {
		return nil
	}

	// figure out our default target type
	var tabletType topodatapb.TabletType
	if *initTabletType != "" {
		if *targetTabletType != "" {
			log.Fatalf("cannot specify both target_tablet_type and init_tablet_type parameters (as they might conflict)")
		}

		// use the type specified on the command line
		var err error
		tabletType, err = topoproto.ParseTabletType(*initTabletType)
		if err != nil {
			log.Fatalf("Invalid init tablet type %v: %v", *initTabletType, err)
		}

		if tabletType == topodatapb.TabletType_MASTER {
			// We disallow MASTER, so we don't have to change
			// shard.MasterAlias, and deal with the corner cases.
			log.Fatalf("init_tablet_type cannot be %v", tabletType)
		}

	} else if *targetTabletType != "" {
		if strings.ToUpper(*targetTabletType) == topodatapb.TabletType_name[int32(topodatapb.TabletType_MASTER)] {
			log.Fatalf("target_tablet_type cannot be '%v'. Use '%v' instead.", tabletType, topodatapb.TabletType_REPLICA)
		}

		// use spare, the healthcheck will turn us into what
		// we need to be eventually
		tabletType = topodatapb.TabletType_SPARE

	} else {
		log.Fatalf("if init tablet is enabled, one of init_tablet_type or target_tablet_type needs to be specified")
	}

	// create a context for this whole operation
	ctx, cancel := context.WithTimeout(agent.batchCtx, *initTimeout)
	defer cancel()

	// since we're assigned to a shard, make sure it exists, see if
	// we are its master, and update its cells list if necessary
	if *initKeyspace == "" || *initShard == "" {
		log.Fatalf("if init tablet is enabled and the target type is not idle, init_keyspace and init_shard also need to be specified")
	}
	shard, _, err := topo.ValidateShardName(*initShard)
	if err != nil {
		log.Fatalf("cannot validate shard name: %v", err)
	}

	log.Infof("Reading shard record %v/%v", *initKeyspace, shard)

	// read the shard, create it if necessary
	si, err := topotools.GetOrCreateShard(ctx, agent.TopoServer, *initKeyspace, shard)
	if err != nil {
		return fmt.Errorf("InitTablet cannot GetOrCreateShard shard: %v", err)
	}
	if si.MasterAlias != nil && topoproto.TabletAliasEqual(si.MasterAlias, agent.TabletAlias) {
		// we are the current master for this shard (probably
		// means the master tablet process was just restarted),
		// so InitTablet as master.
		tabletType = topodatapb.TabletType_MASTER
	}

	// See if we need to add the tablet's cell to the shard's cell
	// list.  If we do, it has to be under the shard lock.
	if !si.HasCell(agent.TabletAlias.Cell) {
		actionNode := actionnode.UpdateShard()
		lockPath, err := actionNode.LockShard(ctx, agent.TopoServer, *initKeyspace, shard)
		if err != nil {
			return fmt.Errorf("LockShard(%v/%v) failed: %v", *initKeyspace, shard, err)
		}

		// re-read the shard with the lock
		si, err = agent.TopoServer.GetShard(ctx, *initKeyspace, shard)
		if err != nil {
			return actionNode.UnlockShard(ctx, agent.TopoServer, *initKeyspace, shard, lockPath, err)
		}

		// see if we really need to update it now
		if !si.HasCell(agent.TabletAlias.Cell) {
			si.Cells = append(si.Cells, agent.TabletAlias.Cell)

			// write it back
			if err := agent.TopoServer.UpdateShard(ctx, si); err != nil {
				return actionNode.UnlockShard(ctx, agent.TopoServer, *initKeyspace, shard, lockPath, err)
			}
		}

		// and unlock
		if err := actionNode.UnlockShard(ctx, agent.TopoServer, *initKeyspace, shard, lockPath, nil); err != nil {
			return err
		}
	}
//.........这里部分代码省略.........

// InitTablet initializes the tablet record if necessary.
func (agent *ActionAgent) InitTablet(port, gRPCPort int32) error {
	// it should be either we have all three of init_keyspace,
	// init_shard and init_tablet_type, or none.
	if *initKeyspace == "" && *initShard == "" && *initTabletType == "" {
		// not initializing the record
		return nil
	}
	if *initKeyspace == "" || *initShard == "" || *initTabletType == "" {
		return fmt.Errorf("either need all of init_keyspace, init_shard and init_tablet_type, or none")
	}

	// parse init_tablet_type
	tabletType, err := topoproto.ParseTabletType(*initTabletType)
	if err != nil {
		return fmt.Errorf("invalid init_tablet_type %v: %v", *initTabletType, err)
	}
	if tabletType == topodatapb.TabletType_MASTER {
		// We disallow MASTER, so we don't have to change
		// shard.MasterAlias, and deal with the corner cases.
		return fmt.Errorf("init_tablet_type cannot be master, use replica instead")
	}

	// parse and validate shard name
	shard, _, err := topo.ValidateShardName(*initShard)
	if err != nil {
		return fmt.Errorf("cannot validate shard name %v: %v", *initShard, err)
	}

	// create a context for this whole operation
	ctx, cancel := context.WithTimeout(agent.batchCtx, *initTimeout)
	defer cancel()

	// read the shard, create it if necessary
	log.Infof("Reading shard record %v/%v", *initKeyspace, shard)
	si, err := agent.TopoServer.GetOrCreateShard(ctx, *initKeyspace, shard)
	if err != nil {
		return fmt.Errorf("InitTablet cannot GetOrCreateShard shard: %v", err)
	}
	if si.MasterAlias != nil && topoproto.TabletAliasEqual(si.MasterAlias, agent.TabletAlias) {
		// We're marked as master in the shard record, which could mean the master
		// tablet process was just restarted. However, we need to check if a new
		// master is in the process of taking over. In that case, it will let us
		// know by forcibly updating the old master's tablet record.
		oldTablet, err := agent.TopoServer.GetTablet(ctx, agent.TabletAlias)
		switch err {
		case topo.ErrNoNode:
			// There's no existing tablet record, so we can assume
			// no one has left us a message to step down.
			tabletType = topodatapb.TabletType_MASTER
		case nil:
			if oldTablet.Type == topodatapb.TabletType_MASTER {
				// We're marked as master in the shard record,
				// and our existing tablet record agrees.
				tabletType = topodatapb.TabletType_MASTER
			}
		default:
			return fmt.Errorf("InitTablet failed to read existing tablet record: %v", err)
		}
	}

	// See if we need to add the tablet's cell to the shard's cell list.
	if !si.HasCell(agent.TabletAlias.Cell) {
		si, err = agent.TopoServer.UpdateShardFields(ctx, *initKeyspace, shard, func(si *topo.ShardInfo) error {
			if si.HasCell(agent.TabletAlias.Cell) {
				// Someone else already did it.
				return topo.ErrNoUpdateNeeded
			}
			si.Cells = append(si.Cells, agent.TabletAlias.Cell)
			return nil
		})
		if err != nil {
			return fmt.Errorf("couldn't add tablet's cell to shard record: %v", err)
		}
	}
	log.Infof("Initializing the tablet for type %v", tabletType)

	// figure out the hostname
	hostname := *tabletHostname
	if hostname != "" {
		log.Infof("Using hostname: %v from -tablet_hostname flag.", hostname)
	} else {
		hostname, err := netutil.FullyQualifiedHostname()
		if err != nil {
			return err
		}
		log.Infof("Using detected machine hostname: %v To change this, fix your machine network configuration or override it with -tablet_hostname.", hostname)
	}

	// create and populate tablet record
	tablet := &topodatapb.Tablet{
		Alias:          agent.TabletAlias,
		Hostname:       hostname,
		PortMap:        make(map[string]int32),
		Keyspace:       *initKeyspace,
		Shard:          *initShard,
		Type:           tabletType,
		DbNameOverride: *initDbNameOverride,
		Tags:           initTags,
	}
//.........这里部分代码省略.........

func (wr *Wrangler) exportVtnsToZkns(ctx context.Context, zconn zk.Conn, vtnsAddrPath, zknsAddrPath string) ([]string, error) {
	zknsPaths := make([]string, 0, 32)
	parts := strings.Split(vtnsAddrPath, "/")
	if len(parts) != 8 && len(parts) != 9 {
		return nil, fmt.Errorf("Invalid leaf zk path: %v", vtnsAddrPath)
	}
	cell := parts[2]
	keyspace := parts[5]
	shard := parts[6]
	tabletTypeStr := parts[7]
	if tabletTypeStr == "action" || tabletTypeStr == "actionlog" {
		return nil, nil
	}
	tabletType, err := topoproto.ParseTabletType(tabletTypeStr)
	if err != nil {
		return nil, err
	}
	addrs, _, err := wr.ts.GetEndPoints(ctx, cell, keyspace, shard, tabletType)
	if err != nil {
		return nil, err
	}

	// Write the individual endpoints and compute the SRV entries.
	vtoccAddrs := LegacyZknsAddrs{make([]string, 0, 8)}
	defaultAddrs := LegacyZknsAddrs{make([]string, 0, 8)}
	for i, entry := range addrs.Entries {
		zknsAddrPath := fmt.Sprintf("%v/%v", zknsAddrPath, i)
		zknsPaths = append(zknsPaths, zknsAddrPath)
		zknsAddr := zkns.ZknsAddr{
			Host:    entry.Host,
			PortMap: entry.PortMap,
		}
		err := writeAddr(zconn, zknsAddrPath, &zknsAddr)
		if err != nil {
			return nil, err
		}
		defaultAddrs.Endpoints = append(defaultAddrs.Endpoints, zknsAddrPath)
		vtoccAddrs.Endpoints = append(vtoccAddrs.Endpoints, zknsAddrPath+":vt")
	}

	// Prune any zkns entries that are no longer referenced by the
	// shard graph.
	deleteIdx := len(addrs.Entries)
	for {
		zknsStaleAddrPath := fmt.Sprintf("%v/%v", zknsAddrPath, deleteIdx)
		// A "delete" is a write of sorts - just communicate up that nothing
		// needs to be done to this node.
		zknsPaths = append(zknsPaths, zknsStaleAddrPath)
		err := zconn.Delete(zknsStaleAddrPath, -1)
		if zookeeper.IsError(err, zookeeper.ZNONODE) {
			break
		}
		if err != nil {
			return nil, err
		}
		deleteIdx++
	}

	// Write the VDNS entries for both vtocc and mysql
	vtoccVdnsPath := fmt.Sprintf("%v/vt.vdns", zknsAddrPath)
	zknsPaths = append(zknsPaths, vtoccVdnsPath)
	if err = writeAddrs(zconn, vtoccVdnsPath, &vtoccAddrs); err != nil {
		return nil, err
	}

	defaultVdnsPath := fmt.Sprintf("%v.vdns", zknsAddrPath)
	zknsPaths = append(zknsPaths, defaultVdnsPath)
	if err = writeAddrs(zconn, defaultVdnsPath, &defaultAddrs); err != nil {
		return nil, err
	}
	return zknsPaths, nil
}

//.........这里部分代码省略.........
			return nil, err
		}

		// Perform an action on a tablet.
		if r.Method == "POST" {
			if err := r.ParseForm(); err != nil {
				return nil, err
			}
			action := r.FormValue("action")
			if action == "" {
				return nil, errors.New("must specify action")
			}
			return actions.ApplyTabletAction(ctx, action, tabletAlias, r), nil
		}

		// Get the tablet record.
		t, err := ts.GetTablet(ctx, tabletAlias)
		// Pass the embedded proto directly or jsonpb will panic.
		return t.Tablet, err
	})

	// Healthcheck real time status per (cell, keyspace, tablet type, metric).
	handleCollection("tablet_statuses", func(r *http.Request) (interface{}, error) {
		targetPath := getItemPath(r.URL.Path)

		// Get the heatmap data based on query parameters.
		if targetPath == "" {
			if err := r.ParseForm(); err != nil {
				return nil, err
			}
			keyspace := r.FormValue("keyspace")
			cell := r.FormValue("cell")
			tabletType := r.FormValue("type")
			_, err := topoproto.ParseTabletType(tabletType)
			// Excluding the case where parse fails because all tabletTypes was chosen.
			if err != nil && tabletType != "all" {
				return nil, fmt.Errorf("invalid tablet type: %v ", err)
			}
			metric := r.FormValue("metric")

			// Setting default values if none was specified in the query params.
			if keyspace == "" {
				keyspace = "all"
			}
			if cell == "" {
				cell = "all"
			}
			if tabletType == "" {
				tabletType = "all"
			}
			if metric == "" {
				metric = "health"
			}

			if realtimeStats == nil {
				return nil, fmt.Errorf("realtimeStats not initialized")
			}

			heatmap, err := realtimeStats.heatmapData(keyspace, cell, tabletType, metric)
			if err != nil {
				return nil, fmt.Errorf("couldn't get heatmap data: %v", err)
			}
			return heatmap, nil
		}

		return nil, fmt.Errorf("invalid target path: %q  expected path: ?keyspace=<keyspace>&cell=<cell>&type=<type>&metric=<metric>", targetPath)

//.........这里部分代码省略.........
				return nil, errors.New("cell param required")
			}
			return ts.GetTabletsByCell(ctx, cell)
		}

		// Get tablet health.
		if parts := strings.Split(tabletPath, "/"); len(parts) == 2 && parts[1] == "health" {
			tabletAlias, err := topoproto.ParseTabletAlias(parts[0])
			if err != nil {
				return nil, err
			}
			return tabletHealthCache.Get(ctx, tabletAlias)
		}

		tabletAlias, err := topoproto.ParseTabletAlias(tabletPath)
		if err != nil {
			return nil, err
		}

		// Perform an action on a tablet.
		if r.Method == "POST" {
			if err := r.ParseForm(); err != nil {
				return nil, err
			}
			action := r.FormValue("action")
			if action == "" {
				return nil, errors.New("must specify action")
			}
			return actions.ApplyTabletAction(ctx, action, tabletAlias, r), nil
		}

		// Get the tablet record.
		return ts.GetTablet(ctx, tabletAlias)
	})

	// EndPoints
	handleCollection("endpoints", func(r *http.Request) (interface{}, error) {
		// We expect cell/keyspace/shard/tabletType.
		epPath := getItemPath(r.URL.Path)
		parts := strings.Split(epPath, "/")
		if len(parts) != 4 {
			return nil, fmt.Errorf("invalid cell/keyspace/shard/tabletType: %q", epPath)
		}

		if parts[3] == "" {
			// tabletType is empty, so list the tablet types.
			return ts.GetSrvTabletTypesPerShard(ctx, parts[0], parts[1], parts[2])
		}

		tabletType, err := topoproto.ParseTabletType(parts[3])
		if err != nil {
			return nil, fmt.Errorf("invalid tablet type %v: %v", parts[3], err)
		}

		// Get the endpoints object for a specific type.
		ep, _, err := ts.GetEndPoints(ctx, parts[0], parts[1], parts[2], tabletType)
		return ep, err
	})

	// Schema Change
	http.HandleFunc(apiPrefix+"schema/apply", func(w http.ResponseWriter, r *http.Request) {
		req := struct{ Keyspace, SQL string }{}
		if err := unmarshalRequest(r, &req); err != nil {
			httpErrorf(w, r, "can't unmarshal request: %v", err)
			return
		}

		executor := schemamanager.NewTabletExecutor(
			tmclient.NewTabletManagerClient(),
			ts)

		schemamanager.Run(ctx,
			schemamanager.NewUIController(req.SQL, req.Keyspace, w), executor)
	})

	// VSchema
	http.HandleFunc(apiPrefix+"vschema/", func(w http.ResponseWriter, r *http.Request) {
		// Save VSchema
		if r.Method == "POST" {
			vschema, err := ioutil.ReadAll(r.Body)
			if err != nil {
				httpErrorf(w, r, "can't read request body: %v", err)
				return
			}
			if err := ts.SaveVSchema(ctx, string(vschema)); err != nil {
				httpErrorf(w, r, "can't save vschema: %v", err)
			}
			return
		}

		// Get VSchema
		vschema, err := ts.GetVSchema(ctx)
		if err != nil {
			httpErrorf(w, r, "can't get vschema: %v", err)
			return
		}
		w.Header().Set("Content-Type", jsonContentType)
		w.Write([]byte(vschema))
	})
}