func (client *fakeTabletManagerClient) GetSchema(ctx context.Context, tablet *topodatapb.Tablet, tables, excludeTables []string, includeViews bool) (*tabletmanagerdatapb.SchemaDefinition, error) {
	result, ok := client.schemaDefinitions[topoproto.TabletDbName(tablet)]
	if !ok {
		return nil, fmt.Errorf("unknown database: %s", topoproto.TabletDbName(tablet))
	}
	return result, nil
}

// loadBlacklistRules loads and builds the blacklist query rules
func (agent *ActionAgent) loadBlacklistRules(tablet *topodatapb.Tablet, blacklistedTables []string) (err error) {
	blacklistRules := tabletserver.NewQueryRules()
	if len(blacklistedTables) > 0 {
		// tables, first resolve wildcards
		tables, err := mysqlctl.ResolveTables(agent.MysqlDaemon, topoproto.TabletDbName(tablet), blacklistedTables)
		if err != nil {
			return err
		}

		// Verify that at least one table matches the wildcards, so
		// that we don't add a rule to blacklist all tables
		if len(tables) > 0 {
			log.Infof("Blacklisting tables %v", strings.Join(tables, ", "))
			qr := tabletserver.NewQueryRule("enforce blacklisted tables", "blacklisted_table", tabletserver.QRFailRetry)
			for _, t := range tables {
				qr.AddTableCond(t)
			}
			blacklistRules.Add(qr)
		}
	}

	loadRuleErr := agent.QueryServiceControl.SetQueryRules(blacklistQueryRules, blacklistRules)
	if loadRuleErr != nil {
		log.Warningf("Fail to load query rule set %s: %s", blacklistQueryRules, loadRuleErr)
	}
	return nil
}

// findDestinationMasters finds for each destination shard the current master.
func (scw *SplitCloneWorker) findDestinationMasters(ctx context.Context) error {
	scw.setState(WorkerStateFindTargets)

	// Make sure we find a master for each destination shard and log it.
	scw.wr.Logger().Infof("Finding a MASTER tablet for each destination shard...")
	for _, si := range scw.destinationShards {
		waitCtx, waitCancel := context.WithTimeout(ctx, *waitForHealthyTabletsTimeout)
		defer waitCancel()
		if err := scw.tsc.WaitForTablets(waitCtx, scw.cell, si.Keyspace(), si.ShardName(), []topodatapb.TabletType{topodatapb.TabletType_MASTER}); err != nil {
			return fmt.Errorf("cannot find MASTER tablet for destination shard for %v/%v (in cell: %v): %v", si.Keyspace(), si.ShardName(), scw.cell, err)
		}
		masters := scw.tsc.GetHealthyTabletStats(si.Keyspace(), si.ShardName(), topodatapb.TabletType_MASTER)
		if len(masters) == 0 {
			return fmt.Errorf("cannot find MASTER tablet for destination shard for %v/%v (in cell: %v) in HealthCheck: empty TabletStats list", si.Keyspace(), si.ShardName(), scw.cell)
		}
		master := masters[0]

		// Get the MySQL database name of the tablet.
		keyspaceAndShard := topoproto.KeyspaceShardString(si.Keyspace(), si.ShardName())
		scw.destinationDbNames[keyspaceAndShard] = topoproto.TabletDbName(master.Tablet)

		// TODO(mberlin): Verify on the destination master that the
		// _vt.blp_checkpoint table has the latest schema.

		scw.wr.Logger().Infof("Using tablet %v as destination master for %v/%v", topoproto.TabletAliasString(master.Tablet.Alias), si.Keyspace(), si.ShardName())
	}
	scw.wr.Logger().Infof("NOTE: The used master of a destination shard might change over the course of the copy e.g. due to a reparent. The HealthCheck module will track and log master changes and any error message will always refer the actually used master address.")

	return nil
}

func (agent *ActionAgent) allowQueries(tablet *pbt.Tablet, blacklistedTables []string) error {
	// if the query service is already running, we're not starting it again
	if agent.QueryServiceControl.IsServing() {
		return nil
	}

	// only for real instances
	if agent.DBConfigs != nil {
		// Update our DB config to match the info we have in the tablet
		if agent.DBConfigs.App.DbName == "" {
			agent.DBConfigs.App.DbName = topoproto.TabletDbName(tablet)
		}
		agent.DBConfigs.App.Keyspace = tablet.Keyspace
		agent.DBConfigs.App.Shard = tablet.Shard
		if tablet.Type != pbt.TabletType_MASTER {
			agent.DBConfigs.App.EnableInvalidator = true
		} else {
			agent.DBConfigs.App.EnableInvalidator = false
		}
	}

	err := agent.loadKeyspaceAndBlacklistRules(tablet, blacklistedTables)
	if err != nil {
		return err
	}

	return agent.QueryServiceControl.StartService(&pb.Target{
		Keyspace:   tablet.Keyspace,
		Shard:      tablet.Shard,
		TabletType: tablet.Type,
	}, agent.DBConfigs, agent.SchemaOverrides, agent.MysqlDaemon)
}

// PreflightSchema will try out the schema change
// Should be called under RPCWrapLockAction.
func (agent *ActionAgent) PreflightSchema(ctx context.Context, change string) (*tmutils.SchemaChangeResult, error) {
	// get the db name from the tablet
	dbName := topoproto.TabletDbName(agent.Tablet())

	// and preflight the change
	return agent.MysqlDaemon.PreflightSchemaChange(dbName, change)
}

// ExecuteFetchAsDba is part of the tmclient.TabletManagerClient interface.
func (client *Client) ExecuteFetchAsDba(ctx context.Context, tablet *topodatapb.Tablet, usePool bool, query []byte, maxRows int, disableBinlogs, reloadSchema bool) (*querypb.QueryResult, error) {
	var c tabletmanagerservicepb.TabletManagerClient
	var err error
	if usePool {
		c, err = client.dialPool(tablet)
		if err != nil {
			return nil, err
		}
	} else {
		var cc *grpc.ClientConn
		cc, c, err = client.dial(tablet)
		if err != nil {
			return nil, err
		}
		defer cc.Close()
	}

	response, err := c.ExecuteFetchAsDba(ctx, &tabletmanagerdatapb.ExecuteFetchAsDbaRequest{
		Query:          query,
		DbName:         topoproto.TabletDbName(tablet),
		MaxRows:        uint64(maxRows),
		DisableBinlogs: disableBinlogs,
		ReloadSchema:   reloadSchema,
	})
	if err != nil {
		return nil, err
	}
	return response.Result, nil
}

// loadKeyspaceAndBlacklistRules does what the name suggests:
// 1. load and build keyrange query rules
// 2. load and build blacklist query rules
func (agent *ActionAgent) loadKeyspaceAndBlacklistRules(tablet *pbt.Tablet, blacklistedTables []string) (err error) {
	// Keyrange rules
	keyrangeRules := tabletserver.NewQueryRules()
	if key.KeyRangeIsPartial(tablet.KeyRange) {
		log.Infof("Restricting to keyrange: %v", tablet.KeyRange)
		dmlPlans := []struct {
			planID   planbuilder.PlanType
			onAbsent bool
		}{
			{planbuilder.PlanInsertPK, true},
			{planbuilder.PlanInsertSubquery, true},
			{planbuilder.PlanPassDML, false},
			{planbuilder.PlanDMLPK, false},
			{planbuilder.PlanDMLSubquery, false},
			{planbuilder.PlanUpsertPK, false},
		}
		for _, plan := range dmlPlans {
			qr := tabletserver.NewQueryRule(
				fmt.Sprintf("enforce keyspace_id range for %v", plan.planID),
				fmt.Sprintf("keyspace_id_not_in_range_%v", plan.planID),
				tabletserver.QRFail,
			)
			qr.AddPlanCond(plan.planID)
			err := qr.AddBindVarCond("keyspace_id", plan.onAbsent, true, tabletserver.QRNotIn, tablet.KeyRange)
			if err != nil {
				return fmt.Errorf("Unable to add keyspace rule: %v", err)
			}
			keyrangeRules.Add(qr)
		}
	}

	// Blacklisted tables
	blacklistRules := tabletserver.NewQueryRules()
	if len(blacklistedTables) > 0 {
		// tables, first resolve wildcards
		tables, err := mysqlctl.ResolveTables(agent.MysqlDaemon, topoproto.TabletDbName(tablet), blacklistedTables)
		if err != nil {
			return err
		}
		log.Infof("Blacklisting tables %v", strings.Join(tables, ", "))
		qr := tabletserver.NewQueryRule("enforce blacklisted tables", "blacklisted_table", tabletserver.QRFailRetry)
		for _, t := range tables {
			qr.AddTableCond(t)
		}
		blacklistRules.Add(qr)
	}
	// Push all three sets of QueryRules to TabletServerRpcService
	loadRuleErr := agent.QueryServiceControl.SetQueryRules(keyrangeQueryRules, keyrangeRules)
	if loadRuleErr != nil {
		log.Warningf("Fail to load query rule set %s: %s", keyrangeQueryRules, loadRuleErr)
	}

	loadRuleErr = agent.QueryServiceControl.SetQueryRules(blacklistQueryRules, blacklistRules)
	if loadRuleErr != nil {
		log.Warningf("Fail to load query rule set %s: %s", blacklistQueryRules, loadRuleErr)
	}
	return nil
}

// PreflightSchema will try out the schema changes in "changes".
func (agent *ActionAgent) PreflightSchema(ctx context.Context, changes []string) ([]*tabletmanagerdatapb.SchemaChangeResult, error) {
	if err := agent.lock(ctx); err != nil {
		return nil, err
	}
	defer agent.unlock()

	// get the db name from the tablet
	dbName := topoproto.TabletDbName(agent.Tablet())

	// and preflight the change
	return agent.MysqlDaemon.PreflightSchemaChange(dbName, changes)
}

// ApplySchema will apply a schema change
// Should be called under RPCWrapLockAction.
func (agent *ActionAgent) ApplySchema(ctx context.Context, change *tmutils.SchemaChange) (*tmutils.SchemaChangeResult, error) {
	// get the db name from the tablet
	dbName := topoproto.TabletDbName(agent.Tablet())

	// apply the change
	scr, err := agent.MysqlDaemon.ApplySchemaChange(dbName, change)
	if err != nil {
		return nil, err
	}

	// and if it worked, reload the schema
	agent.ReloadSchema(ctx)
	return scr, nil
}

// ExecuteFetchAsDba is part of the tmclient.TabletManagerClient interface.
func (client *Client) ExecuteFetchAsDba(ctx context.Context, tablet *topodatapb.Tablet, query []byte, maxRows int, disableBinlogs, reloadSchema bool) (*querypb.QueryResult, error) {
	c, err := client.dialPool(tablet)
	if err != nil {
		return nil, err
	}
	response, err := c.ExecuteFetchAsDba(ctx, &tabletmanagerdatapb.ExecuteFetchAsDbaRequest{
		Query:          query,
		DbName:         topoproto.TabletDbName(tablet),
		MaxRows:        uint64(maxRows),
		DisableBinlogs: disableBinlogs,
		ReloadSchema:   reloadSchema,
	})
	if err != nil {
		return nil, err
	}
	return response.Result, nil
}

// RefreshMap reads the right data from topo.Server and makes sure
// we're playing the right logs.
func (blm *BinlogPlayerMap) RefreshMap(ctx context.Context, tablet *pb.Tablet, keyspaceInfo *topo.KeyspaceInfo, shardInfo *topo.ShardInfo) {
	log.Infof("Refreshing map of binlog players")
	if shardInfo == nil {
		log.Warningf("Could not read shardInfo, not changing anything")
		return
	}

	if len(shardInfo.SourceShards) > 0 && keyspaceInfo == nil {
		log.Warningf("Could not read keyspaceInfo, not changing anything")
		return
	}

	blm.mu.Lock()
	if blm.dbConfig.DbName == "" {
		blm.dbConfig.DbName = topoproto.TabletDbName(tablet)
	}

	// get the existing sources and build a map of sources to remove
	toRemove := make(map[uint32]bool)
	hadPlayers := false
	for source := range blm.players {
		toRemove[source] = true
		hadPlayers = true
	}

	// for each source, add it if not there, and delete from toRemove
	for _, sourceShard := range shardInfo.SourceShards {
		blm.addPlayer(ctx, tablet.Alias.Cell, keyspaceInfo.ShardingColumnType, tablet.KeyRange, sourceShard, topoproto.TabletDbName(tablet))
		delete(toRemove, sourceShard.Uid)
	}
	hasPlayers := len(shardInfo.SourceShards) > 0

	// remove all entries from toRemove
	for source := range toRemove {
		blm.players[source].Stop()
		delete(blm.players, source)
	}

	blm.mu.Unlock()

	if hadPlayers && !hasPlayers {
		// We're done streaming, so turn off special playback settings.
		blm.mysqld.DisableBinlogPlayback()
	}
}

// findTargets phase:
// - find one rdonly in the source shard
// - mark it as 'worker' pointing back to us
// - get the aliases of all the targets
func (vscw *VerticalSplitCloneWorker) findTargets(ctx context.Context) error {
	vscw.setState(WorkerStateFindTargets)

	// find an appropriate tablet in the source shard
	var err error
	vscw.sourceAlias, err = FindWorkerTablet(ctx, vscw.wr, vscw.cleaner, nil /* tsc */, vscw.cell, vscw.sourceKeyspace, "0", vscw.minHealthyRdonlyTablets)
	if err != nil {
		return fmt.Errorf("FindWorkerTablet() failed for %v/%v/0: %v", vscw.cell, vscw.sourceKeyspace, err)
	}
	vscw.wr.Logger().Infof("Using tablet %v as the source", topoproto.TabletAliasString(vscw.sourceAlias))

	// get the tablet info for it
	shortCtx, cancel := context.WithTimeout(ctx, *remoteActionsTimeout)
	ti, err := vscw.wr.TopoServer().GetTablet(shortCtx, vscw.sourceAlias)
	cancel()
	if err != nil {
		return fmt.Errorf("cannot read tablet %v: %v", topoproto.TabletAliasString(vscw.sourceAlias), err)
	}
	vscw.sourceTablet = ti.Tablet

	// stop replication on it
	shortCtx, cancel = context.WithTimeout(ctx, *remoteActionsTimeout)
	err = vscw.wr.TabletManagerClient().StopSlave(shortCtx, vscw.sourceTablet)
	cancel()
	if err != nil {
		return fmt.Errorf("cannot stop replication on tablet %v", topoproto.TabletAliasString(vscw.sourceAlias))
	}

	wrangler.RecordStartSlaveAction(vscw.cleaner, vscw.sourceTablet)

	// Initialize healthcheck and add destination shards to it.
	vscw.healthCheck = discovery.NewHealthCheck(*remoteActionsTimeout, *healthcheckRetryDelay, *healthCheckTimeout)
	vscw.tsc = discovery.NewTabletStatsCache(vscw.healthCheck, vscw.cell)
	watcher := discovery.NewShardReplicationWatcher(vscw.wr.TopoServer(), vscw.healthCheck,
		vscw.cell, vscw.destinationKeyspace, vscw.destinationShard,
		*healthCheckTopologyRefresh, discovery.DefaultTopoReadConcurrency)
	vscw.destinationShardWatchers = append(vscw.destinationShardWatchers, watcher)

	// Make sure we find a master for each destination shard and log it.
	vscw.wr.Logger().Infof("Finding a MASTER tablet for each destination shard...")
	waitCtx, waitCancel := context.WithTimeout(ctx, *waitForHealthyTabletsTimeout)
	defer waitCancel()
	if err := vscw.tsc.WaitForTablets(waitCtx, vscw.cell, vscw.destinationKeyspace, vscw.destinationShard, []topodatapb.TabletType{topodatapb.TabletType_MASTER}); err != nil {
		return fmt.Errorf("cannot find MASTER tablet for destination shard for %v/%v (in cell: %v): %v", vscw.destinationKeyspace, vscw.destinationShard, vscw.cell, err)
	}
	masters := vscw.tsc.GetHealthyTabletStats(vscw.destinationKeyspace, vscw.destinationShard, topodatapb.TabletType_MASTER)
	if len(masters) == 0 {
		return fmt.Errorf("cannot find MASTER tablet for destination shard for %v/%v (in cell: %v) in HealthCheck: empty TabletStats list", vscw.destinationKeyspace, vscw.destinationShard, vscw.cell)
	}
	master := masters[0]

	// Get the MySQL database name of the tablet.
	keyspaceAndShard := topoproto.KeyspaceShardString(vscw.destinationKeyspace, vscw.destinationShard)
	vscw.destinationDbNames[keyspaceAndShard] = topoproto.TabletDbName(master.Tablet)

	// TODO(mberlin): Verify on the destination master that the
	// _vt.blp_checkpoint table has the latest schema.

	vscw.wr.Logger().Infof("Using tablet %v as destination master for %v/%v", topoproto.TabletAliasString(master.Tablet.Alias), vscw.destinationKeyspace, vscw.destinationShard)
	vscw.wr.Logger().Infof("NOTE: The used master of a destination shard might change over the course of the copy e.g. due to a reparent. The HealthCheck module will track and log master changes and any error message will always refer the actually used master address.")

	return nil
}

// Start validates and updates the topology records for the tablet, and performs
// the initial state change callback to start tablet services.
func (agent *ActionAgent) Start(ctx context.Context, mysqlPort, vtPort, gRPCPort int32) error {
	var err error
	if _, err = agent.readTablet(ctx); err != nil {
		return err
	}

	// find our hostname as fully qualified, and IP
	hostname := *tabletHostname
	if hostname == "" {
		hostname, err = netutil.FullyQualifiedHostname()
		if err != nil {
			return err
		}
	}
	ipAddrs, err := net.LookupHost(hostname)
	if err != nil {
		return err
	}
	ipAddr := ipAddrs[0]

	// Update bind addr for mysql and query service in the tablet node.
	f := func(tablet *pb.Tablet) error {
		tablet.Hostname = hostname
		tablet.Ip = ipAddr
		if tablet.PortMap == nil {
			tablet.PortMap = make(map[string]int32)
		}
		if mysqlPort != 0 {
			// only overwrite mysql port if we know it, otherwise
			// leave it as is.
			tablet.PortMap["mysql"] = mysqlPort
		}
		if vtPort != 0 {
			tablet.PortMap["vt"] = vtPort
		} else {
			delete(tablet.PortMap, "vt")
		}
		delete(tablet.PortMap, "vts")
		if gRPCPort != 0 {
			tablet.PortMap["grpc"] = gRPCPort
		} else {
			delete(tablet.PortMap, "grpc")
		}
		return nil
	}
	if err := agent.TopoServer.UpdateTabletFields(ctx, agent.Tablet().Alias, f); err != nil {
		return err
	}

	// Reread to get the changes we just made
	tablet, err := agent.readTablet(ctx)
	if err != nil {
		return err
	}

	if err = agent.verifyTopology(ctx); err != nil {
		return err
	}

	if err = agent.verifyServingAddrs(ctx); err != nil {
		return err
	}

	// initialize tablet server
	if !agent.DBConfigs.IsZero() {
		// Only for real instances
		// Update our DB config to match the info we have in the tablet
		if agent.DBConfigs.App.DbName == "" {
			agent.DBConfigs.App.DbName = topoproto.TabletDbName(tablet.Tablet)
		}
		agent.DBConfigs.App.Keyspace = tablet.Keyspace
		agent.DBConfigs.App.Shard = tablet.Shard
	}
	if err := agent.QueryServiceControl.InitDBConfig(pbq.Target{
		Keyspace:   tablet.Keyspace,
		Shard:      tablet.Shard,
		TabletType: tablet.Type,
	}, agent.DBConfigs, agent.SchemaOverrides, agent.MysqlDaemon); err != nil {
		return fmt.Errorf("failed to InitDBConfig: %v", err)
	}

	// and update our state
	oldTablet := &pb.Tablet{}
	if err = agent.updateState(ctx, oldTablet, "Start"); err != nil {
		log.Warningf("Initial updateState failed, will need a state change before running properly: %v", err)
	}
	return nil
}

func (agent *ActionAgent) restoreDataLocked(ctx context.Context, logger logutil.Logger, deleteBeforeRestore bool) error {
	// change type to RESTORE (using UpdateTabletFields so it's
	// always authorized)
	var originalType topodatapb.TabletType
	if _, err := agent.TopoServer.UpdateTabletFields(ctx, agent.TabletAlias, func(tablet *topodatapb.Tablet) error {
		originalType = tablet.Type
		tablet.Type = topodatapb.TabletType_RESTORE
		return nil
	}); err != nil {
		return fmt.Errorf("Cannot change type to RESTORE: %v", err)
	}

	// let's update our internal state (stop query service and other things)
	if err := agent.refreshTablet(ctx, "restore from backup"); err != nil {
		return fmt.Errorf("failed to update state before restore: %v", err)
	}

	// Try to restore. Depending on the reason for failure, we may be ok.
	// If we're not ok, return an error and the agent will log.Fatalf,
	// causing the process to be restarted and the restore retried.
	// Record local metadata values based on the original type.
	localMetadata := agent.getLocalMetadataValues(originalType)
	tablet := agent.Tablet()
	dir := fmt.Sprintf("%v/%v", tablet.Keyspace, tablet.Shard)
	pos, err := mysqlctl.Restore(ctx, agent.MysqlDaemon, dir, *restoreConcurrency, agent.hookExtraEnv(), localMetadata, logger, deleteBeforeRestore, topoproto.TabletDbName(tablet))
	switch err {
	case nil:
		// Reconnect to master.
		if err := agent.startReplication(ctx, pos); err != nil {
			return err
		}
	case mysqlctl.ErrNoBackup:
		// No-op, starting with empty database.
	case mysqlctl.ErrExistingDB:
		// No-op, assuming we've just restarted.
	default:
		return fmt.Errorf("Can't restore backup: %v", err)
	}

	// Change type back to original type if we're ok to serve.
	if _, err := agent.TopoServer.UpdateTabletFields(ctx, tablet.Alias, func(tablet *topodatapb.Tablet) error {
		tablet.Type = originalType
		return nil
	}); err != nil {
		return fmt.Errorf("Cannot change type back to %v: %v", originalType, err)
	}

	// let's update our internal state (start query service and other things)
	if err := agent.refreshTablet(ctx, "after restore from backup"); err != nil {
		return fmt.Errorf("failed to update state after backup: %v", err)
	}

	return nil
}

// GetSchema returns the schema.
// Should be called under RPCWrap.
func (agent *ActionAgent) GetSchema(ctx context.Context, tables, excludeTables []string, includeViews bool) (*tabletmanagerdatapb.SchemaDefinition, error) {
	return agent.MysqlDaemon.GetSchema(topoproto.TabletDbName(agent.Tablet()), tables, excludeTables, includeViews)
}

// Start validates and updates the topology records for the tablet, and performs
// the initial state change callback to start tablet services.
// If initUpdateStream is set, update stream service will also be registered.
func (agent *ActionAgent) Start(ctx context.Context, mysqlPort, vtPort, gRPCPort int32, initUpdateStream bool) error {
	// find our hostname as fully qualified, and IP
	hostname := *tabletHostname
	if hostname == "" {
		var err error
		hostname, err = netutil.FullyQualifiedHostname()
		if err != nil {
			return err
		}
	}
	ipAddrs, err := net.LookupHost(hostname)
	if err != nil {
		return err
	}
	ipAddr := ipAddrs[0]

	// Update bind addr for mysql and query service in the tablet node.
	f := func(tablet *topodatapb.Tablet) error {
		tablet.Hostname = hostname
		tablet.Ip = ipAddr
		if tablet.PortMap == nil {
			tablet.PortMap = make(map[string]int32)
		}
		if mysqlPort != 0 {
			// only overwrite mysql port if we know it, otherwise
			// leave it as is.
			tablet.PortMap["mysql"] = mysqlPort
		}
		if vtPort != 0 {
			tablet.PortMap["vt"] = vtPort
		} else {
			delete(tablet.PortMap, "vt")
		}
		delete(tablet.PortMap, "vts")
		if gRPCPort != 0 {
			tablet.PortMap["grpc"] = gRPCPort
		} else {
			delete(tablet.PortMap, "grpc")
		}

		// Save the original tablet for ownership tests later.
		agent.initialTablet = tablet
		return nil
	}
	if _, err := agent.TopoServer.UpdateTabletFields(ctx, agent.TabletAlias, f); err != nil {
		return err
	}

	// Verify the topology is correct.
	agent.verifyTopology(ctx)

	// Get and fix the dbname if necessary, only for real instances.
	if !agent.DBConfigs.IsZero() {
		dbname := topoproto.TabletDbName(agent.initialTablet)

		// Update our DB config to match the info we have in the tablet
		if agent.DBConfigs.App.DbName == "" {
			agent.DBConfigs.App.DbName = dbname
		}
		if agent.DBConfigs.Filtered.DbName == "" {
			agent.DBConfigs.Filtered.DbName = dbname
		}
	}

	// create and register the RPC services from UpdateStream
	// (it needs the dbname, so it has to be delayed up to here,
	// but it has to be before updateState below that may use it)
	if initUpdateStream {
		us := binlog.NewUpdateStream(agent.MysqlDaemon, agent.DBConfigs.App.DbName)
		agent.UpdateStream = us
		servenv.OnRun(func() {
			us.RegisterService()
		})
	}
	servenv.OnTerm(func() {
		// Disable UpdateStream (if any) upon entering lameduck.
		// We do this regardless of initUpdateStream, since agent.UpdateStream
		// may have been set from elsewhere.
		if agent.UpdateStream != nil {
			agent.UpdateStream.Disable()
		}
	})

	// initialize tablet server
	if err := agent.QueryServiceControl.InitDBConfig(querypb.Target{
		Keyspace:   agent.initialTablet.Keyspace,
		Shard:      agent.initialTablet.Shard,
		TabletType: agent.initialTablet.Type,
	}, agent.DBConfigs, agent.MysqlDaemon); err != nil {
		return fmt.Errorf("failed to InitDBConfig: %v", err)
	}

	// export a few static variables
	if agent.exportStats {
		statsKeyspace := stats.NewString("TabletKeyspace")
		statsShard := stats.NewString("TabletShard")
		statsKeyRangeStart := stats.NewString("TabletKeyRangeStart")
//.........这里部分代码省略.........

// Start validates and updates the topology records for the tablet, and performs
// the initial state change callback to start tablet services.
// If initUpdateStream is set, update stream service will also be registered.
func (agent *ActionAgent) Start(ctx context.Context, mysqlPort, vtPort, gRPCPort int32, initUpdateStream bool) error {
	var err error
	if _, err = agent.updateTabletFromTopo(ctx); err != nil {
		return err
	}

	// find our hostname as fully qualified, and IP
	hostname := *tabletHostname
	if hostname == "" {
		hostname, err = netutil.FullyQualifiedHostname()
		if err != nil {
			return err
		}
	}
	ipAddrs, err := net.LookupHost(hostname)
	if err != nil {
		return err
	}
	ipAddr := ipAddrs[0]

	// Update bind addr for mysql and query service in the tablet node.
	f := func(tablet *pb.Tablet) error {
		tablet.Hostname = hostname
		tablet.Ip = ipAddr
		if tablet.PortMap == nil {
			tablet.PortMap = make(map[string]int32)
		}
		if mysqlPort != 0 {
			// only overwrite mysql port if we know it, otherwise
			// leave it as is.
			tablet.PortMap["mysql"] = mysqlPort
		}
		if vtPort != 0 {
			tablet.PortMap["vt"] = vtPort
		} else {
			delete(tablet.PortMap, "vt")
		}
		delete(tablet.PortMap, "vts")
		if gRPCPort != 0 {
			tablet.PortMap["grpc"] = gRPCPort
		} else {
			delete(tablet.PortMap, "grpc")
		}
		return nil
	}
	if err := agent.TopoServer.UpdateTabletFields(ctx, agent.Tablet().Alias, f); err != nil {
		return err
	}

	// Reread to get the changes we just made
	tablet, err := agent.updateTabletFromTopo(ctx)
	if err != nil {
		return err
	}

	if err = agent.verifyTopology(ctx); err != nil {
		return err
	}

	if err = agent.verifyServingAddrs(ctx); err != nil {
		return err
	}

	// get and fix the dbname if necessary
	if !agent.DBConfigs.IsZero() {
		// Only for real instances
		// Update our DB config to match the info we have in the tablet
		if agent.DBConfigs.App.DbName == "" {
			agent.DBConfigs.App.DbName = topoproto.TabletDbName(tablet.Tablet)
		}
		agent.DBConfigs.App.Keyspace = tablet.Keyspace
		agent.DBConfigs.App.Shard = tablet.Shard
	}

	// create and register the RPC services from UpdateStream
	// (it needs the dbname, so it has to be delayed up to here,
	// but it has to be before updateState below that may use it)
	if initUpdateStream {
		us := binlog.NewUpdateStream(agent.MysqlDaemon, agent.DBConfigs.App.DbName)
		us.RegisterService()
		agent.UpdateStream = us
	}

	// initialize tablet server
	if err := agent.QueryServiceControl.InitDBConfig(pbq.Target{
		Keyspace:   tablet.Keyspace,
		Shard:      tablet.Shard,
		TabletType: tablet.Type,
	}, agent.DBConfigs, agent.SchemaOverrides, agent.MysqlDaemon); err != nil {
		return fmt.Errorf("failed to InitDBConfig: %v", err)
	}

	// export a few static variables
	if agent.exportStats {
		statsKeyspace := stats.NewString("TabletKeyspace")
		statsShard := stats.NewString("TabletShard")
		statsKeyRangeStart := stats.NewString("TabletKeyRangeStart")
//.........这里部分代码省略.........

// DbName is usually implied by keyspace. Having the shard information in the
// database name complicates mysql replication.
func (ti *TabletInfo) DbName() string {
	return topoproto.TabletDbName(ti.Tablet)
}

// generateChunks returns an array of chunks to use for splitting up a table
// into multiple data chunks. It only works for tables with a primary key
// whose first column is a numeric type.
func generateChunks(ctx context.Context, wr *wrangler.Wrangler, tablet *topodatapb.Tablet, td *tabletmanagerdatapb.TableDefinition, minTableSizeForSplit uint64, chunkCount int) ([]chunk, error) {
	if len(td.PrimaryKeyColumns) == 0 {
		// No explicit primary key. Cannot chunk the rows then.
		return singleCompleteChunk, nil
	}
	if td.DataLength < minTableSizeForSplit {
		// Table is too small to split up.
		return singleCompleteChunk, nil
	}
	if chunkCount == 1 {
		return singleCompleteChunk, nil
	}

	// Get the MIN and MAX of the leading column of the primary key.
	query := fmt.Sprintf("SELECT MIN(%v), MAX(%v) FROM %v.%v", td.PrimaryKeyColumns[0], td.PrimaryKeyColumns[0], topoproto.TabletDbName(tablet), td.Name)
	shortCtx, cancel := context.WithTimeout(ctx, *remoteActionsTimeout)
	qr, err := wr.TabletManagerClient().ExecuteFetchAsApp(shortCtx, tablet, true, []byte(query), 1)
	cancel()
	if err != nil {
		return nil, fmt.Errorf("Cannot determine MIN and MAX of the first primary key column. ExecuteFetchAsApp: %v", err)
	}
	if len(qr.Rows) != 1 {
		return nil, fmt.Errorf("Cannot determine MIN and MAX of the first primary key column. Zero rows were returned for the following query: %v", query)
	}

	result := sqltypes.Proto3ToResult(qr)
	min := result.Rows[0][0].ToNative()
	max := result.Rows[0][1].ToNative()

	if min == nil || max == nil {
		wr.Logger().Infof("Not splitting table %v into multiple chunks, min or max is NULL: %v", td.Name, qr.Rows[0])
		return singleCompleteChunk, nil
	}

	// TODO(mberlin): Write a unit test for this part of the function.
	chunks := make([]chunk, chunkCount)
	switch min := min.(type) {
	case int64:
		max := max.(int64)
		interval := (max - min) / int64(chunkCount)
		if interval == 0 {
			wr.Logger().Infof("Not splitting table %v into multiple chunks, interval=0: %v to %v", td.Name, min, max)
			return singleCompleteChunk, nil
		}

		start := min
		for i := 0; i < chunkCount; i++ {
			end := start + interval
			chunk, err := toChunk(start, end)
			if err != nil {
				return nil, err
			}
			chunks[i] = chunk
			start = end
		}
	case uint64:
		max := max.(uint64)
		interval := (max - min) / uint64(chunkCount)
		if interval == 0 {
			wr.Logger().Infof("Not splitting table %v into multiple chunks, interval=0: %v to %v", td.Name, min, max)
			return singleCompleteChunk, nil
		}

		start := min
		for i := 0; i < chunkCount; i++ {
			end := start + interval
			chunk, err := toChunk(start, end)
			if err != nil {
				return nil, err
			}
			chunks[i] = chunk
			start = end
		}
	case float64:
		max := max.(float64)
		interval := (max - min) / float64(chunkCount)
		if interval == 0 {
			wr.Logger().Infof("Not splitting table %v into multiple chunks, interval=0: %v to %v", td.Name, min, max)
			return singleCompleteChunk, nil
		}

		start := min
		for i := 0; i < chunkCount; i++ {
			end := start + interval
			chunk, err := toChunk(start, end)
			if err != nil {
				return nil, err
			}
			chunks[i] = chunk
			start = end
		}
	default:
		wr.Logger().Infof("Not splitting table %v into multiple chunks, primary key not numeric.", td.Name)
		return singleCompleteChunk, nil
	}

	// Clear out the MIN and MAX on the first and last chunk respectively
//.........这里部分代码省略.........

//.........这里部分代码省略.........
	event.DispatchUpdate(ev, "resetting replication on all tablets")
	wg := sync.WaitGroup{}
	rec := concurrency.AllErrorRecorder{}
	for alias, tabletInfo := range tabletMap {
		wg.Add(1)
		go func(alias topodatapb.TabletAlias, tabletInfo *topo.TabletInfo) {
			defer wg.Done()
			wr.logger.Infof("resetting replication on tablet %v", topoproto.TabletAliasString(&alias))
			if err := wr.TabletManagerClient().ResetReplication(ctx, tabletInfo); err != nil {
				rec.RecordError(fmt.Errorf("Tablet %v ResetReplication failed (either fix it, or Scrap it): %v", topoproto.TabletAliasString(&alias), err))
			}
		}(alias, tabletInfo)
	}
	wg.Wait()
	if err := rec.Error(); err != nil {
		return err
	}

	// Tell the new master to break its slaves, return its replication
	// position
	wr.logger.Infof("initializing master on %v", topoproto.TabletAliasString(masterElectTabletAlias))
	event.DispatchUpdate(ev, "initializing master")
	rp, err := wr.TabletManagerClient().InitMaster(ctx, masterElectTabletInfo)
	if err != nil {
		return err
	}

	// Now tell the new master to insert the reparent_journal row,
	// and tell everybody else to become a slave of the new master,
	// and wait for the row in the reparent_journal table.
	// We start all these in parallel, to handle the semi-sync
	// case: for the master to be able to commit its row in the
	// reparent_journal table, it needs connected slaves.
	event.DispatchUpdate(ev, "reparenting all tablets")
	now := time.Now().UnixNano()
	wgMaster := sync.WaitGroup{}
	wgSlaves := sync.WaitGroup{}
	var masterErr error
	for alias, tabletInfo := range tabletMap {
		if topoproto.TabletAliasEqual(&alias, masterElectTabletAlias) {
			wgMaster.Add(1)
			go func(alias topodatapb.TabletAlias, tabletInfo *topo.TabletInfo) {
				defer wgMaster.Done()
				wr.logger.Infof("populating reparent journal on new master %v", topoproto.TabletAliasString(&alias))
				masterErr = wr.TabletManagerClient().PopulateReparentJournal(ctx, tabletInfo, now, initShardMasterOperation, &alias, rp)
			}(alias, tabletInfo)
		} else {
			wgSlaves.Add(1)
			go func(alias topodatapb.TabletAlias, tabletInfo *topo.TabletInfo) {
				defer wgSlaves.Done()
				wr.logger.Infof("initializing slave %v", topoproto.TabletAliasString(&alias))
				if err := wr.TabletManagerClient().InitSlave(ctx, tabletInfo, masterElectTabletAlias, rp, now); err != nil {
					rec.RecordError(fmt.Errorf("Tablet %v InitSlave failed: %v", topoproto.TabletAliasString(&alias), err))
				}
			}(alias, tabletInfo)
		}
	}

	// After the master is done, we can update the shard record
	// (note with semi-sync, it also means at least one slave is done)
	wgMaster.Wait()
	if masterErr != nil {
		wgSlaves.Wait()
		return fmt.Errorf("failed to PopulateReparentJournal on master: %v", masterErr)
	}
	if !topoproto.TabletAliasEqual(shardInfo.MasterAlias, masterElectTabletAlias) {
		if _, err := wr.ts.UpdateShardFields(ctx, keyspace, shard, func(s *topodatapb.Shard) error {
			s.MasterAlias = masterElectTabletAlias
			return nil
		}); err != nil {
			wgSlaves.Wait()
			return fmt.Errorf("failed to update shard master record: %v", err)
		}
	}

	// Wait for the slaves to complete. If some of them fail, we
	// don't want to rebuild the shard serving graph (the failure
	// will most likely be a timeout, and our context will be
	// expired, so the rebuild will fail anyway)
	wgSlaves.Wait()
	if err := rec.Error(); err != nil {
		return err
	}

	// Create database if necessary on the master. Slaves will get it too through
	// replication. Since the user called InitShardMaster, they've told us to
	// assume that whatever data is on all the slaves is what they intended.
	// If the database doesn't exist, it means the user intends for these tablets
	// to begin serving with no data (i.e. first time initialization).
	createDB := fmt.Sprintf("CREATE DATABASE IF NOT EXISTS `%s`", topoproto.TabletDbName(masterElectTabletInfo.Tablet))
	if _, err := wr.TabletManagerClient().ExecuteFetchAsDba(ctx, masterElectTabletInfo, createDB, 1, false, true); err != nil {
		return fmt.Errorf("failed to create database: %v", err)
	}

	// Then we rebuild the entire serving graph for the shard,
	// to account for all changes.
	event.DispatchUpdate(ev, "rebuilding shard graph")
	_, err = wr.RebuildShardGraph(ctx, keyspace, shard, nil)
	return err
}