legacy_split_clone.go

/*
Copyright 2017 Google Inc.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package worker

// TODO(mberlin): Remove this file when SplitClone supports merge-sorting
// primary key columns based on the MySQL collation.

import (
	"fmt"
	"html/template"
	"io"
	"strings"
	"sync"
	"time"

	"github.com/xsec-lab/go/vt/vterrors"

	"golang.org/x/net/context"

	"github.com/xsec-lab/go/event"
	"github.com/xsec-lab/go/sqlescape"
	"github.com/xsec-lab/go/sync2"
	"github.com/xsec-lab/go/vt/binlog/binlogplayer"
	"github.com/xsec-lab/go/vt/discovery"
	"github.com/xsec-lab/go/vt/throttler"
	"github.com/xsec-lab/go/vt/topo"
	"github.com/xsec-lab/go/vt/topo/topoproto"
	"github.com/xsec-lab/go/vt/topotools"
	"github.com/xsec-lab/go/vt/vtgate/vindexes"
	"github.com/xsec-lab/go/vt/worker/events"
	"github.com/xsec-lab/go/vt/wrangler"

	binlogdatapb "github.com/xsec-lab/go/vt/proto/binlogdata"
	tabletmanagerdatapb "github.com/xsec-lab/go/vt/proto/tabletmanagerdata"
	topodatapb "github.com/xsec-lab/go/vt/proto/topodata"
)

// LegacySplitCloneWorker will clone the data within a keyspace from a
// source set of shards to a destination set of shards.
type LegacySplitCloneWorker struct {
	StatusWorker

	wr                      *wrangler.Wrangler
	cell                    string
	keyspace                string
	shard                   string
	excludeTables           []string
	sourceReaderCount       int
	destinationPackCount    int
	destinationWriterCount  int
	minHealthyRdonlyTablets int
	maxTPS                  int64
	cleaner                 *wrangler.Cleaner

	// populated during WorkerStateInit, read-only after that
	keyspaceInfo      *topo.KeyspaceInfo
	sourceShards      []*topo.ShardInfo
	destinationShards []*topo.ShardInfo

	// populated during WorkerStateFindTargets, read-only after that
	sourceAliases []*topodatapb.TabletAlias
	sourceTablets []*topodatapb.Tablet
	// healthCheck tracks the health of all MASTER and REPLICA tablets.
	// It must be closed at the end of the command.
	healthCheck discovery.HealthCheck
	tsc         *discovery.TabletStatsCache
	// destinationShardWatchers contains a TopologyWatcher for each destination
	// shard. It updates the list of tablets in the healthcheck if replicas are
	// added/removed.
	// Each watcher must be stopped at the end of the command.
	destinationShardWatchers []*discovery.TopologyWatcher
	// destinationDbNames stores for each destination keyspace/shard the MySQL
	// database name.
	// Example Map Entry: test_keyspace/-80 => vt_test_keyspace
	destinationDbNames map[string]string
	// destionThrottlers stores for each destination keyspace/shard the
	// Throttler instance which will limit the write throughput.
	destinationThrottlers map[string]*throttler.Throttler

	// populated during WorkerStateCopy
	// tableStatusList holds the status for each table.
	tableStatusList tableStatusList

	ev *events.SplitClone
}

// NewLegacySplitCloneWorker returns a new LegacySplitCloneWorker object.
func NewLegacySplitCloneWorker(wr *wrangler.Wrangler, cell, keyspace, shard string, excludeTables []string, sourceReaderCount, destinationPackCount, destinationWriterCount, minHealthyRdonlyTablets int, maxTPS int64) (Worker, error) {
	if maxTPS != throttler.MaxRateModuleDisabled {
		wr.Logger().Infof("throttling enabled and set to a max of %v transactions/second", maxTPS)
	}
	if maxTPS != throttler.MaxRateModuleDisabled && maxTPS < int64(destinationWriterCount) {
		return nil, fmt.Errorf("-max_tps must be >= -destination_writer_count: %v >= %v", maxTPS, destinationWriterCount)
	}
	return &LegacySplitCloneWorker{
		StatusWorker:            NewStatusWorker(),
		wr:                      wr,
		cell:                    cell,
		keyspace:                keyspace,
		shard:                   shard,
		excludeTables:           excludeTables,
		sourceReaderCount:       sourceReaderCount,
		destinationPackCount:    destinationPackCount,
		destinationWriterCount:  destinationWriterCount,
		minHealthyRdonlyTablets: minHealthyRdonlyTablets,
		maxTPS:                  maxTPS,
		cleaner:                 &wrangler.Cleaner{},

		destinationDbNames:    make(map[string]string),
		destinationThrottlers: make(map[string]*throttler.Throttler),

		ev: &events.SplitClone{
			Cell:          cell,
			Keyspace:      keyspace,
			Shard:         shard,
			ExcludeTables: excludeTables,
		},
	}, nil
}

func (scw *LegacySplitCloneWorker) setState(state StatusWorkerState) {
	scw.SetState(state)
	event.DispatchUpdate(scw.ev, state.String())
}

func (scw *LegacySplitCloneWorker) setErrorState(err error) {
	scw.SetState(WorkerStateError)
	event.DispatchUpdate(scw.ev, "error: "+err.Error())
}

func (scw *LegacySplitCloneWorker) formatSources() string {
	result := ""
	for _, alias := range scw.sourceAliases {
		result += " " + topoproto.TabletAliasString(alias)
	}
	return result
}

// StatusAsHTML implements the Worker interface
func (scw *LegacySplitCloneWorker) StatusAsHTML() template.HTML {
	state := scw.State()

	result := "<b>Working on:</b> " + scw.keyspace + "/" + scw.shard + "</br>\n"
	result += "<b>State:</b> " + state.String() + "</br>\n"
	switch state {
	case WorkerStateCloneOnline:
		result += "<b>Running</b>:</br>\n"
		result += "<b>Copying from</b>: " + scw.formatSources() + "</br>\n"
		statuses, eta := scw.tableStatusList.format()
		result += "<b>ETA</b>: " + eta.String() + "</br>\n"
		result += strings.Join(statuses, "</br>\n")
	case WorkerStateDone:
		result += "<b>Success</b>:</br>\n"
		statuses, _ := scw.tableStatusList.format()
		result += strings.Join(statuses, "</br>\n")
	}

	return template.HTML(result)
}

// StatusAsText implements the Worker interface
func (scw *LegacySplitCloneWorker) StatusAsText() string {
	state := scw.State()

	result := "Working on: " + scw.keyspace + "/" + scw.shard + "\n"
	result += "State: " + state.String() + "\n"
	switch state {
	case WorkerStateCloneOnline:
		result += "Running:\n"
		result += "Copying from: " + scw.formatSources() + "\n"
		statuses, eta := scw.tableStatusList.format()
		result += "ETA: " + eta.String() + "\n"
		result += strings.Join(statuses, "\n")
	case WorkerStateDone:
		result += "Success:\n"
		statuses, _ := scw.tableStatusList.format()
		result += strings.Join(statuses, "\n")
	}
	return result
}

// Run implements the Worker interface
func (scw *LegacySplitCloneWorker) Run(ctx context.Context) error {
	resetVars()

	// Run the command.
	err := scw.run(ctx)

	// Cleanup.
	scw.setState(WorkerStateCleanUp)
	// Reverse any changes e.g. setting the tablet type of a source RDONLY tablet.
	cerr := scw.cleaner.CleanUp(scw.wr)
	if cerr != nil {
		if err != nil {
			scw.wr.Logger().Errorf("CleanUp failed in addition to job error: %v", cerr)
		} else {
			err = cerr
		}
	}

	// Stop Throttlers.
	for _, throttler := range scw.destinationThrottlers {
		throttler.Close()
	}
	// Stop healthcheck.
	for _, watcher := range scw.destinationShardWatchers {
		watcher.Stop()
	}
	if scw.healthCheck != nil {
		if err := scw.healthCheck.Close(); err != nil {
			scw.wr.Logger().Errorf("HealthCheck.Close() failed: %v", err)
		}
	}

	if err != nil {
		scw.setErrorState(err)
		return err
	}
	scw.setState(WorkerStateDone)
	return nil
}

func (scw *LegacySplitCloneWorker) run(ctx context.Context) error {
	// first state: read what we need to do
	if err := scw.init(ctx); err != nil {
		return vterrors.Wrap(err, "init() failed")
	}
	if err := checkDone(ctx); err != nil {
		return err
	}

	// second state: find targets
	if err := scw.findTargets(ctx); err != nil {
		return vterrors.Wrap(err, "findTargets() failed")
	}
	if err := checkDone(ctx); err != nil {
		return err
	}

	// third state: copy data
	if err := scw.copy(ctx); err != nil {
		return vterrors.Wrap(err, "copy() failed")
	}

	return nil
}

// init phase:
// - read the destination keyspace, make sure it has 'servedFrom' values
func (scw *LegacySplitCloneWorker) init(ctx context.Context) error {
	scw.setState(WorkerStateInit)
	var err error

	// read the keyspace and validate it
	shortCtx, cancel := context.WithTimeout(ctx, *remoteActionsTimeout)
	scw.keyspaceInfo, err = scw.wr.TopoServer().GetKeyspace(shortCtx, scw.keyspace)
	cancel()
	if err != nil {
		return vterrors.Wrapf(err, "cannot read keyspace %v", scw.keyspace)
	}

	// find the OverlappingShards in the keyspace
	shortCtx, cancel = context.WithTimeout(ctx, *remoteActionsTimeout)
	osList, err := topotools.FindOverlappingShards(shortCtx, scw.wr.TopoServer(), scw.keyspace)
	cancel()
	if err != nil {
		return vterrors.Wrapf(err, "cannot FindOverlappingShards in %v", scw.keyspace)
	}

	// find the shard we mentioned in there, if any
	os := topotools.OverlappingShardsForShard(osList, scw.shard)
	if os == nil {
		return fmt.Errorf("the specified shard %v/%v is not in any overlapping shard", scw.keyspace, scw.shard)
	}
	scw.wr.Logger().Infof("Found overlapping shards: %+v\n", os)

	// one side should have served types, the other one none,
	// figure out wich is which, then double check them all
	if len(os.Left[0].ServedTypes) > 0 {
		scw.sourceShards = os.Left
		scw.destinationShards = os.Right
	} else {
		scw.sourceShards = os.Right
		scw.destinationShards = os.Left
	}

	// Verify that filtered replication is not already enabled.
	for _, si := range scw.destinationShards {
		if len(si.SourceShards) > 0 {
			return fmt.Errorf("destination shard %v/%v has filtered replication already enabled from a previous resharding (ShardInfo is set)."+
				" This requires manual intervention e.g. use vtctl SourceShardDelete to remove it",
				si.Keyspace(), si.ShardName())
		}
	}

	// validate all serving types
	servingTypes := []topodatapb.TabletType{topodatapb.TabletType_MASTER, topodatapb.TabletType_REPLICA, topodatapb.TabletType_RDONLY}
	for _, st := range servingTypes {
		for _, si := range scw.sourceShards {
			if si.GetServedType(st) == nil {
				return fmt.Errorf("source shard %v/%v is not serving type %v", si.Keyspace(), si.ShardName(), st)
			}
		}
	}
	for _, si := range scw.destinationShards {
		if len(si.ServedTypes) > 0 {
			return fmt.Errorf("destination shard %v/%v is serving some types", si.Keyspace(), si.ShardName())
		}
	}

	return nil
}

// 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 (scw *LegacySplitCloneWorker) findTargets(ctx context.Context) error {
	scw.setState(WorkerStateFindTargets)
	var err error

	// find an appropriate tablet in the source shards
	scw.sourceAliases = make([]*topodatapb.TabletAlias, len(scw.sourceShards))
	for i, si := range scw.sourceShards {
		scw.sourceAliases[i], err = FindWorkerTablet(ctx, scw.wr, scw.cleaner, scw.tsc, scw.cell, si.Keyspace(), si.ShardName(), scw.minHealthyRdonlyTablets, topodatapb.TabletType_RDONLY)
		if err != nil {
			return vterrors.Wrapf(err, "FindWorkerTablet() failed for %v/%v/%v", scw.cell, si.Keyspace(), si.ShardName())
		}
		scw.wr.Logger().Infof("Using tablet %v as source for %v/%v", topoproto.TabletAliasString(scw.sourceAliases[i]), si.Keyspace(), si.ShardName())
	}

	// get the tablet info for them, and stop their replication
	scw.sourceTablets = make([]*topodatapb.Tablet, len(scw.sourceAliases))
	for i, alias := range scw.sourceAliases {
		shortCtx, cancel := context.WithTimeout(ctx, *remoteActionsTimeout)
		ti, err := scw.wr.TopoServer().GetTablet(shortCtx, alias)
		cancel()
		if err != nil {
			return vterrors.Wrapf(err, "cannot read tablet %v", topoproto.TabletAliasString(alias))
		}
		scw.sourceTablets[i] = ti.Tablet

		shortCtx, cancel = context.WithTimeout(ctx, *remoteActionsTimeout)
		err = scw.wr.TabletManagerClient().StopSlave(shortCtx, scw.sourceTablets[i])
		cancel()
		if err != nil {
			return fmt.Errorf("cannot stop replication on tablet %v", topoproto.TabletAliasString(alias))
		}

		wrangler.RecordStartSlaveAction(scw.cleaner, scw.sourceTablets[i])
	}

	// Initialize healthcheck and add destination shards to it.
	scw.healthCheck = discovery.NewHealthCheck(*healthcheckRetryDelay, *healthCheckTimeout)
	scw.tsc = discovery.NewTabletStatsCache(scw.healthCheck, scw.wr.TopoServer(), scw.cell)
	for _, si := range scw.destinationShards {
		watcher := discovery.NewShardReplicationWatcher(scw.wr.TopoServer(), scw.healthCheck,
			scw.cell, si.Keyspace(), si.ShardName(),
			*healthCheckTopologyRefresh, discovery.DefaultTopoReadConcurrency)
		scw.destinationShardWatchers = append(scw.destinationShardWatchers, watcher)
	}

	// 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, 10*time.Second)
		defer waitCancel()
		if err := scw.tsc.WaitForTablets(waitCtx, scw.cell, si.Keyspace(), si.ShardName(), topodatapb.TabletType_MASTER); err != nil {
			return vterrors.Wrapf(err, "cannot find MASTER tablet for destination shard for %v/%v", si.Keyspace(), si.ShardName())
		}
		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 HealthCheck: empty TabletStats list", si.Keyspace(), si.ShardName())
		}
		master := masters[0]

		// Get the MySQL database name of the tablet.
		shortCtx, cancel := context.WithTimeout(ctx, *remoteActionsTimeout)
		ti, err := scw.wr.TopoServer().GetTablet(shortCtx, master.Tablet.Alias)
		cancel()
		if err != nil {
			return vterrors.Wrapf(err, "cannot get the TabletInfo for destination master (%v) to find out its db name", topoproto.TabletAliasString(master.Tablet.Alias))
		}
		keyspaceAndShard := topoproto.KeyspaceShardString(si.Keyspace(), si.ShardName())
		scw.destinationDbNames[keyspaceAndShard] = ti.DbName()

		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.")

	// Set up the throttler for each destination shard.
	for _, si := range scw.destinationShards {
		keyspaceAndShard := topoproto.KeyspaceShardString(si.Keyspace(), si.ShardName())
		t, err := throttler.NewThrottler(
			keyspaceAndShard, "transactions", scw.destinationWriterCount, scw.maxTPS, throttler.ReplicationLagModuleDisabled)
		if err != nil {
			return vterrors.Wrap(err, "cannot instantiate throttler")
		}
		scw.destinationThrottlers[keyspaceAndShard] = t
	}

	return nil
}

// copy phase:
//	- copy the data from source tablets to destination masters (with replication on)
// Assumes that the schema has already been created on each destination tablet
// (probably from vtctl's CopySchemaShard)
func (scw *LegacySplitCloneWorker) copy(ctx context.Context) error {
	scw.setState(WorkerStateCloneOffline)
	start := time.Now()
	defer func() {
		statsStateDurationsNs.Set(string(WorkerStateCloneOffline), time.Now().Sub(start).Nanoseconds())
	}()

	// get source schema from the first shard
	// TODO(alainjobart): for now, we assume the schema is compatible
	// on all source shards. Furthermore, we estimate the number of rows
	// in each source shard for each table to be about the same
	// (rowCount is used to estimate an ETA)
	shortCtx, cancel := context.WithTimeout(ctx, *remoteActionsTimeout)
	sourceSchemaDefinition, err := scw.wr.GetSchema(shortCtx, scw.sourceAliases[0], nil, scw.excludeTables, false /* includeViews */)
	cancel()
	if err != nil {
		return vterrors.Wrapf(err, "cannot get schema from source %v", topoproto.TabletAliasString(scw.sourceAliases[0]))
	}
	if len(sourceSchemaDefinition.TableDefinitions) == 0 {
		return fmt.Errorf("no tables matching the table filter in tablet %v", topoproto.TabletAliasString(scw.sourceAliases[0]))
	}
	for _, td := range sourceSchemaDefinition.TableDefinitions {
		if len(td.Columns) == 0 {
			return fmt.Errorf("schema for table %v has no columns", td.Name)
		}
	}
	scw.wr.Logger().Infof("Source tablet 0 has %v tables to copy", len(sourceSchemaDefinition.TableDefinitions))
	scw.tableStatusList.initialize(sourceSchemaDefinition)

	// In parallel, setup the channels to send SQL data chunks to for each destination tablet:
	//
	// mu protects the context for cancelation, and firstError
	mu := sync.Mutex{}
	var firstError error

	ctx, cancelCopy := context.WithCancel(ctx)
	processError := func(format string, args ...interface{}) {
		scw.wr.Logger().Errorf(format, args...)
		mu.Lock()
		if firstError == nil {
			firstError = fmt.Errorf(format, args...)
			cancelCopy()
		}
		mu.Unlock()
	}

	insertChannels := make([]chan string, len(scw.destinationShards))
	destinationWaitGroup := sync.WaitGroup{}
	for shardIndex, si := range scw.destinationShards {
		// we create one channel per destination tablet.  It
		// is sized to have a buffer of a maximum of
		// destinationWriterCount * 2 items, to hopefully
		// always have data. We then have
		// destinationWriterCount go routines reading from it.
		insertChannels[shardIndex] = make(chan string, scw.destinationWriterCount*2)

		go func(keyspace, shard string, insertChannel chan string) {
			for j := 0; j < scw.destinationWriterCount; j++ {
				destinationWaitGroup.Add(1)
				go func(threadID int) {
					defer destinationWaitGroup.Done()

					keyspaceAndShard := topoproto.KeyspaceShardString(keyspace, shard)
					throttler := scw.destinationThrottlers[keyspaceAndShard]
					defer throttler.ThreadFinished(threadID)

					executor := newExecutor(scw.wr, scw.tsc, throttler, keyspace, shard, threadID)
					if err := executor.fetchLoop(ctx, insertChannel); err != nil {
						processError("executer.FetchLoop failed: %v", err)
					}
				}(j)
			}
		}(si.Keyspace(), si.ShardName(), insertChannels[shardIndex])
	}

	// read the vschema if needed
	var keyspaceSchema *vindexes.KeyspaceSchema
	if *useV3ReshardingMode {
		kschema, err := scw.wr.TopoServer().GetVSchema(ctx, scw.keyspace)
		if err != nil {
			return vterrors.Wrapf(err, "cannot load VSchema for keyspace %v", scw.keyspace)
		}
		if kschema == nil {
			return fmt.Errorf("no VSchema for keyspace %v", scw.keyspace)
		}

		keyspaceSchema, err = vindexes.BuildKeyspaceSchema(kschema, scw.keyspace)
		if err != nil {
			return vterrors.Wrapf(err, "cannot build vschema for keyspace %v", scw.keyspace)
		}
	}

	// Now for each table, read data chunks and send them to all
	// insertChannels
	sourceWaitGroup := sync.WaitGroup{}
	for shardIndex := range scw.sourceShards {
		sema := sync2.NewSemaphore(scw.sourceReaderCount, 0)
		for tableIndex, td := range sourceSchemaDefinition.TableDefinitions {
			var keyResolver keyspaceIDResolver
			if *useV3ReshardingMode {
				keyResolver, err = newV3ResolverFromTableDefinition(keyspaceSchema, td)
				if err != nil {
					return vterrors.Wrapf(err, "cannot resolve v3 sharding keys for keyspace %v", scw.keyspace)
				}
			} else {
				keyResolver, err = newV2Resolver(scw.keyspaceInfo, td)
				if err != nil {
					return vterrors.Wrapf(err, "cannot resolve sharding keys for keyspace %v", scw.keyspace)
				}
			}
			rowSplitter := NewRowSplitter(scw.destinationShards, keyResolver)

			chunks, err := generateChunks(ctx, scw.wr, scw.sourceTablets[shardIndex], td, scw.sourceReaderCount, defaultMinRowsPerChunk)
			if err != nil {
				return err
			}
			scw.tableStatusList.setThreadCount(tableIndex, len(chunks)-1)

			for _, c := range chunks {
				sourceWaitGroup.Add(1)
				go func(td *tabletmanagerdatapb.TableDefinition, shardIndex, tableIndex int, chunk chunk) {
					defer sourceWaitGroup.Done()

					sema.Acquire()
					defer sema.Release()

					scw.tableStatusList.threadStarted(tableIndex)
					defer scw.tableStatusList.threadDone(tableIndex)

					// Start streaming from the source tablets.
					tp := newSingleTabletProvider(ctx, scw.wr.TopoServer(), scw.sourceAliases[shardIndex])
					rr, err := NewRestartableResultReader(ctx, scw.wr.Logger(), tp, td, chunk, false /* allowMultipleRetries */)
					if err != nil {
						processError("NewRestartableResultReader failed: %v", err)
						return
					}
					defer rr.Close(ctx)

					// process the data
					dbNames := make([]string, len(scw.destinationShards))
					for i, si := range scw.destinationShards {
						keyspaceAndShard := topoproto.KeyspaceShardString(si.Keyspace(), si.ShardName())
						dbNames[i] = scw.destinationDbNames[keyspaceAndShard]
					}
					if err := scw.processData(ctx, dbNames, td, tableIndex, rr, rowSplitter, insertChannels, scw.destinationPackCount); err != nil {
						processError("processData failed: %v", err)
					}
				}(td, shardIndex, tableIndex, c)
			}
		}
	}
	sourceWaitGroup.Wait()

	for shardIndex := range scw.destinationShards {
		close(insertChannels[shardIndex])
	}
	destinationWaitGroup.Wait()
	if firstError != nil {
		return firstError
	}

	sourcePositions := make([]string, len(scw.sourceShards))
	// get the current position from the sources
	for shardIndex := range scw.sourceShards {
		shortCtx, cancel := context.WithTimeout(ctx, *remoteActionsTimeout)
		status, err := scw.wr.TabletManagerClient().SlaveStatus(shortCtx, scw.sourceTablets[shardIndex])
		cancel()
		if err != nil {
			return err
		}
		sourcePositions[shardIndex] = status.Position
	}

	for _, si := range scw.destinationShards {
		destinationWaitGroup.Add(1)
		go func(keyspace, shard string, kr *topodatapb.KeyRange) {
			defer destinationWaitGroup.Done()
			scw.wr.Logger().Infof("Making and populating vreplication table")

			exc := newExecutor(scw.wr, scw.tsc, nil, keyspace, shard, 0)
			for shardIndex, src := range scw.sourceShards {
				bls := &binlogdatapb.BinlogSource{
					Keyspace: src.Keyspace(),
					Shard:    src.ShardName(),
					KeyRange: kr,
				}
				qr, err := exc.vreplicationExec(ctx, binlogplayer.CreateVReplication("LegacySplitClone", bls, sourcePositions[shardIndex], scw.maxTPS, throttler.ReplicationLagModuleDisabled, time.Now().Unix()))
				if err != nil {
					processError("vreplication queries failed: %v", err)
					break
				}
				if err := scw.wr.SourceShardAdd(ctx, keyspace, shard, uint32(qr.InsertID), src.Keyspace(), src.ShardName(), src.Shard.KeyRange, nil); err != nil {
					processError("could not add source shard: %v", err)
					break
				}
			}
			// refreshState will cause the destination to become non-serving because
			// it's now participating in the resharding workflow.
			if err := exc.refreshState(ctx); err != nil {
				processError("RefreshState failed on tablet %v/%v: %v", keyspace, shard, err)
			}
		}(si.Keyspace(), si.ShardName(), si.KeyRange)
	}
	destinationWaitGroup.Wait()
	return firstError
}

// processData pumps the data out of the provided QueryResultReader.
// It returns any error the source encounters.
func (scw *LegacySplitCloneWorker) processData(ctx context.Context, dbNames []string, td *tabletmanagerdatapb.TableDefinition, tableIndex int, rr ResultReader, rowSplitter *RowSplitter, insertChannels []chan string, destinationPackCount int) error {
	// Store the baseCmd per destination shard because each tablet may have a
	// different dbName.
	baseCmds := make([]string, len(dbNames))
	for i, dbName := range dbNames {
		baseCmds[i] = "INSERT INTO " + sqlescape.EscapeID(dbName) + "." + sqlescape.EscapeID(td.Name) + " (" + strings.Join(escapeAll(td.Columns), ", ") + ") VALUES "
	}
	sr := rowSplitter.StartSplit()
	packCount := 0

	fields := rr.Fields()
	for {
		r, err := rr.Next()
		if err != nil {
			// we are done, see if there was an error
			if err != io.EOF {
				return err
			}

			// send the remainder if any (ignoring
			// the return value, we don't care
			// here if we're aborted)
			if packCount > 0 {
				rowSplitter.Send(fields, sr, baseCmds, insertChannels, ctx.Done())
			}
			return nil
		}

		// Split the rows by keyspace ID, and insert each chunk into each destination
		if err := rowSplitter.Split(sr, r.Rows); err != nil {
			return vterrors.Wrapf(err, "RowSplitter failed for table %v", td.Name)
		}
		scw.tableStatusList.addCopiedRows(tableIndex, len(r.Rows))

		// see if we reach the destination pack count
		packCount++
		if packCount < destinationPackCount {
			continue
		}

		// send the rows to be inserted
		if aborted := rowSplitter.Send(fields, sr, baseCmds, insertChannels, ctx.Done()); aborted {
			return nil
		}

		// and reset our row buffer
		sr = rowSplitter.StartSplit()
		packCount = 0
	}
}