- Throttling-check is now an async routine running once per second

- Throttling variables protected by mutex
- Added `--throttle-additional-flag-file`: `operation pauses when this file exists; hint: keep default, use for throttling multiple gh-osc operations`
- ColumnList is not a `struct` which contains ordinal mapping
- More implicit write changelog + audit changelog
- builder now builds `DELETE` and `INSERT` queries from data it will eventually get from DML event
- Sanity check for binlog_row_image
- Restarting replication to be sure binlog settings apply
- Prepare for accepting `SIGHUP` (reloading configuration)

go/base/context.go

@@ -9,6 +9,7 @@ import (
 	"fmt"
 	"strconv"
 	"strings"
+	"sync"
 	"sync/atomic"
 	"time"
 
@@ -50,18 +51,19 @@ type MigrationContext struct {
 	CurrentLag                          int64
 	MaxLagMillisecondsThrottleThreshold int64
 	ThrottleFlagFile                    string
+	ThrottleAdditionalFlagFile          string
 	TotalRowsCopied                     int64
-	isThrottled                         int64
+	isThrottled                         bool
-	ThrottleReason                      string
+	throttleReason                      string
+	throttleMutex                       *sync.Mutex
 	MaxLoad                             map[string]int64
 
-	OriginalTableColumns             sql.ColumnList
+	OriginalTableColumns             *sql.ColumnList
-	OriginalTableColumnsMap          sql.ColumnsMap
 	OriginalTableUniqueKeys          [](*sql.UniqueKey)
-	GhostTableColumns                sql.ColumnList
+	GhostTableColumns                *sql.ColumnList
 	GhostTableUniqueKeys             [](*sql.UniqueKey)
 	UniqueKey                        *sql.UniqueKey
-	SharedColumns                    sql.ColumnList
+	SharedColumns                    *sql.ColumnList
 	MigrationRangeMinValues          *sql.ColumnValues
 	MigrationRangeMaxValues          *sql.ColumnValues
 	Iteration                        int64
@@ -83,7 +85,8 @@ func newMigrationContext() *MigrationContext {
 		InspectorConnectionConfig:           mysql.NewConnectionConfig(),
 		MasterConnectionConfig:              mysql.NewConnectionConfig(),
 		MaxLagMillisecondsThrottleThreshold: 1000,
-		MaxLoad: make(map[string]int64),
+		MaxLoad:       make(map[string]int64),
+		throttleMutex: &sync.Mutex{},
 	}
 }
 
@@ -97,6 +100,11 @@ func (this *MigrationContext) GetGhostTableName() string {
 	return fmt.Sprintf("_%s_New", this.OriginalTableName)
 }
 
+// GetOldTableName generates the name of the "old" table, into which the original table is renamed.
+func (this *MigrationContext) GetOldTableName() string {
+	return fmt.Sprintf("_%s_Old", this.OriginalTableName)
+}
+
 // GetChangelogTableName generates the name of changelog table, based on original table name
 func (this *MigrationContext) GetChangelogTableName() string {
 	return fmt.Sprintf("_%s_OSC", this.OriginalTableName)
@@ -157,16 +165,17 @@ func (this *MigrationContext) GetIteration() int64 {
 	return atomic.LoadInt64(&this.Iteration)
 }
 
-func (this *MigrationContext) SetThrottled(throttle bool) {
+func (this *MigrationContext) SetThrottled(throttle bool, reason string) {
-	if throttle {
+	this.throttleMutex.Lock()
-		atomic.StoreInt64(&this.isThrottled, 1)
+	defer func() { this.throttleMutex.Unlock() }()
-	} else {
+	this.isThrottled = throttle
-		atomic.StoreInt64(&this.isThrottled, 0)
+	this.throttleReason = reason
-	}
 }
 
-func (this *MigrationContext) IsThrottled() bool {
+func (this *MigrationContext) IsThrottled() (bool, string) {
-	return atomic.LoadInt64(&this.isThrottled) != 0
+	this.throttleMutex.Lock()
+	defer func() { this.throttleMutex.Unlock() }()
+	return this.isThrottled, this.throttleReason
 }
 
 func (this *MigrationContext) ReadMaxLoad(maxLoadList string) error {

go/cmd/gh-osc/main.go

@@ -38,7 +38,8 @@ func main() {
 		migrationContext.ChunkSize = 100000
 	}
 	flag.Int64Var(&migrationContext.MaxLagMillisecondsThrottleThreshold, "max-lag-millis", 1000, "replication lag at which to throttle operation")
-	flag.StringVar(&migrationContext.ThrottleFlagFile, "throttle-flag-file", "/tmp/gh-osc.throttle", "operation pauses when this file exists")
+	flag.StringVar(&migrationContext.ThrottleFlagFile, "throttle-flag-file", "", "operation pauses when this file exists; hint: use a file that is specific to the table being altered")
+	flag.StringVar(&migrationContext.ThrottleAdditionalFlagFile, "throttle-additional-flag-file", "/tmp/gh-osc.throttle", "operation pauses when this file exists; hint: keep default, use for throttling multiple gh-osc operations")
 	maxLoad := flag.String("max-load", "", "Comma delimited status-name=threshold. e.g: 'Threads_running=100,Threads_connected=500'")
 	quiet := flag.Bool("quiet", false, "quiet")
 	verbose := flag.Bool("verbose", false, "verbose")

go/logic/applier.go

@@ -12,6 +12,7 @@ import (
 	"time"
 
 	"github.com/github/gh-osc/go/base"
+	"github.com/github/gh-osc/go/binlog"
 	"github.com/github/gh-osc/go/mysql"
 	"github.com/github/gh-osc/go/sql"
 
@@ -63,7 +64,7 @@ func (this *Applier) validateConnection() error {
 	return nil
 }
 
-// CreateGhostTable creates the ghost table on the master
+// CreateGhostTable creates the ghost table on the applier host
 func (this *Applier) CreateGhostTable() error {
 	query := fmt.Sprintf(`create /* gh-osc */ table %s.%s like %s.%s`,
 		sql.EscapeName(this.migrationContext.DatabaseName),
@@ -82,7 +83,7 @@ func (this *Applier) CreateGhostTable() error {
 	return nil
 }
 
-// CreateGhostTable creates the ghost table on the master
+// AlterGhost applies `alter` statement on ghost table
 func (this *Applier) AlterGhost() error {
 	query := fmt.Sprintf(`alter /* gh-osc */ table %s.%s %s`,
 		sql.EscapeName(this.migrationContext.DatabaseName),
@@ -101,7 +102,7 @@ func (this *Applier) AlterGhost() error {
 	return nil
 }
 
-// CreateChangelogTable creates the changelog table on the master
+// CreateChangelogTable creates the changelog table on the applier host
 func (this *Applier) CreateChangelogTable() error {
 	query := fmt.Sprintf(`create /* gh-osc */ table %s.%s (
 			id bigint auto_increment,
@@ -110,7 +111,7 @@ func (this *Applier) CreateChangelogTable() error {
 			value varchar(255) charset ascii not null,
 			primary key(id),
 			unique key hint_uidx(hint)
-		) auto_increment=2
+		) auto_increment=256
 		`,
 		sql.EscapeName(this.migrationContext.DatabaseName),
 		sql.EscapeName(this.migrationContext.GetChangelogTableName()),
@@ -126,23 +127,33 @@ func (this *Applier) CreateChangelogTable() error {
 	return nil
 }
 
-// DropChangelogTable drops the changelog table on the master
+// dropTable drops a given table on the applied host
-func (this *Applier) DropChangelogTable() error {
+func (this *Applier) dropTable(tableName string) error {
 	query := fmt.Sprintf(`drop /* gh-osc */ table if exists %s.%s`,
 		sql.EscapeName(this.migrationContext.DatabaseName),
-		sql.EscapeName(this.migrationContext.GetChangelogTableName()),
+		sql.EscapeName(tableName),
 	)
-	log.Infof("Droppping changelog table %s.%s",
+	log.Infof("Droppping table %s.%s",
 		sql.EscapeName(this.migrationContext.DatabaseName),
-		sql.EscapeName(this.migrationContext.GetChangelogTableName()),
+		sql.EscapeName(tableName),
 	)
 	if _, err := sqlutils.ExecNoPrepare(this.db, query); err != nil {
 		return err
 	}
-	log.Infof("Changelog table dropped")
+	log.Infof("Table dropped")
 	return nil
 }
 
+// DropChangelogTable drops the changelog table on the applier host
+func (this *Applier) DropChangelogTable() error {
+	return this.dropTable(this.migrationContext.GetChangelogTableName())
+}
+
+// DropGhostTable drops the ghost table on the applier host
+func (this *Applier) DropGhostTable() error {
+	return this.dropTable(this.migrationContext.GetGhostTableName())
+}
+
 // WriteChangelog writes a value to the changelog table.
 // It returns the hint as given, for convenience
 func (this *Applier) WriteChangelog(hint, value string) (string, error) {
@@ -162,12 +173,15 @@ func (this *Applier) WriteChangelog(hint, value string) (string, error) {
 	return hint, err
 }
 
-func (this *Applier) WriteChangelogState(value string) (string, error) {
+func (this *Applier) WriteAndLogChangelog(hint, value string) (string, error) {
-	hint := "state"
 	this.WriteChangelog(hint, value)
 	return this.WriteChangelog(fmt.Sprintf("%s at %d", hint, time.Now().UnixNano()), value)
 }
 
+func (this *Applier) WriteChangelogState(value string) (string, error) {
+	return this.WriteAndLogChangelog("state", value)
+}
+
 // InitiateHeartbeat creates a heartbeat cycle, writing to the changelog table.
 // This is done asynchronously
 func (this *Applier) InitiateHeartbeat() {
@@ -213,7 +227,7 @@ func (this *Applier) InitiateHeartbeat() {
 // ReadMigrationMinValues
 func (this *Applier) ReadMigrationMinValues(uniqueKey *sql.UniqueKey) error {
 	log.Debugf("Reading migration range according to key: %s", uniqueKey.Name)
-	query, err := sql.BuildUniqueKeyMinValuesPreparedQuery(this.migrationContext.DatabaseName, this.migrationContext.OriginalTableName, uniqueKey.Columns)
+	query, err := sql.BuildUniqueKeyMinValuesPreparedQuery(this.migrationContext.DatabaseName, this.migrationContext.OriginalTableName, uniqueKey.Columns.Names)
 	if err != nil {
 		return err
 	}
@@ -222,7 +236,7 @@ func (this *Applier) ReadMigrationMinValues(uniqueKey *sql.UniqueKey) error {
 		return err
 	}
 	for rows.Next() {
-		this.migrationContext.MigrationRangeMinValues = sql.NewColumnValues(len(uniqueKey.Columns))
+		this.migrationContext.MigrationRangeMinValues = sql.NewColumnValues(uniqueKey.Len())
 		if err = rows.Scan(this.migrationContext.MigrationRangeMinValues.ValuesPointers...); err != nil {
 			return err
 		}
@@ -234,7 +248,7 @@ func (this *Applier) ReadMigrationMinValues(uniqueKey *sql.UniqueKey) error {
 // ReadMigrationMinValues
 func (this *Applier) ReadMigrationMaxValues(uniqueKey *sql.UniqueKey) error {
 	log.Debugf("Reading migration range according to key: %s", uniqueKey.Name)
-	query, err := sql.BuildUniqueKeyMaxValuesPreparedQuery(this.migrationContext.DatabaseName, this.migrationContext.OriginalTableName, uniqueKey.Columns)
+	query, err := sql.BuildUniqueKeyMaxValuesPreparedQuery(this.migrationContext.DatabaseName, this.migrationContext.OriginalTableName, uniqueKey.Columns.Names)
 	if err != nil {
 		return err
 	}
@@ -243,7 +257,7 @@ func (this *Applier) ReadMigrationMaxValues(uniqueKey *sql.UniqueKey) error {
 		return err
 	}
 	for rows.Next() {
-		this.migrationContext.MigrationRangeMaxValues = sql.NewColumnValues(len(uniqueKey.Columns))
+		this.migrationContext.MigrationRangeMaxValues = sql.NewColumnValues(uniqueKey.Len())
 		if err = rows.Scan(this.migrationContext.MigrationRangeMaxValues.ValuesPointers...); err != nil {
 			return err
 		}
@@ -272,12 +286,12 @@ func (this *Applier) __unused_IterationIsComplete() (bool, error) {
 		return false, nil
 	}
 	args := sqlutils.Args()
-	compareWithIterationRangeStart, explodedArgs, err := sql.BuildRangePreparedComparison(this.migrationContext.UniqueKey.Columns, this.migrationContext.MigrationIterationRangeMinValues.AbstractValues(), sql.GreaterThanOrEqualsComparisonSign)
+	compareWithIterationRangeStart, explodedArgs, err := sql.BuildRangePreparedComparison(this.migrationContext.UniqueKey.Columns.Names, this.migrationContext.MigrationIterationRangeMinValues.AbstractValues(), sql.GreaterThanOrEqualsComparisonSign)
 	if err != nil {
 		return false, err
 	}
 	args = append(args, explodedArgs...)
-	compareWithRangeEnd, explodedArgs, err := sql.BuildRangePreparedComparison(this.migrationContext.UniqueKey.Columns, this.migrationContext.MigrationRangeMaxValues.AbstractValues(), sql.LessThanComparisonSign)
+	compareWithRangeEnd, explodedArgs, err := sql.BuildRangePreparedComparison(this.migrationContext.UniqueKey.Columns.Names, this.migrationContext.MigrationRangeMaxValues.AbstractValues(), sql.LessThanComparisonSign)
 	if err != nil {
 		return false, err
 	}
@@ -317,7 +331,7 @@ func (this *Applier) CalculateNextIterationRangeEndValues() (hasFurtherRange boo
 	query, explodedArgs, err := sql.BuildUniqueKeyRangeEndPreparedQuery(
 		this.migrationContext.DatabaseName,
 		this.migrationContext.OriginalTableName,
-		this.migrationContext.UniqueKey.Columns,
+		this.migrationContext.UniqueKey.Columns.Names,
 		this.migrationContext.MigrationIterationRangeMinValues.AbstractValues(),
 		this.migrationContext.MigrationRangeMaxValues.AbstractValues(),
 		this.migrationContext.ChunkSize,
@@ -330,7 +344,7 @@ func (this *Applier) CalculateNextIterationRangeEndValues() (hasFurtherRange boo
 	if err != nil {
 		return hasFurtherRange, err
 	}
-	iterationRangeMaxValues := sql.NewColumnValues(len(this.migrationContext.UniqueKey.Columns))
+	iterationRangeMaxValues := sql.NewColumnValues(this.migrationContext.UniqueKey.Len())
 	for rows.Next() {
 		if err = rows.Scan(iterationRangeMaxValues.ValuesPointers...); err != nil {
 			return hasFurtherRange, err
@@ -360,9 +374,9 @@ func (this *Applier) ApplyIterationInsertQuery() (chunkSize int64, rowsAffected
 		this.migrationContext.DatabaseName,
 		this.migrationContext.OriginalTableName,
 		this.migrationContext.GetGhostTableName(),
-		this.migrationContext.SharedColumns,
+		this.migrationContext.SharedColumns.Names,
 		this.migrationContext.UniqueKey.Name,
-		this.migrationContext.UniqueKey.Columns,
+		this.migrationContext.UniqueKey.Columns.Names,
 		this.migrationContext.MigrationIterationRangeMinValues.AbstractValues(),
 		this.migrationContext.MigrationIterationRangeMaxValues.AbstractValues(),
 		this.migrationContext.GetIteration() == 0,
@@ -422,3 +436,12 @@ func (this *Applier) ShowStatusVariable(variableName string) (result int64, err
 	}
 	return result, nil
 }
+
+func (this *Applier) BuildDMLEventQuery(dmlEvent *binlog.BinlogDMLEvent) (result string, err error) {
+	switch dmlEvent.DML {
+	case binlog.DeleteDML:
+		{
+		}
+	}
+	return result, err
+}

go/logic/inspect.go

@@ -44,6 +44,9 @@ func (this *Inspector) InitDBConnections() (err error) {
 	if err := this.validateGrants(); err != nil {
 		return err
 	}
+	if err := this.restartReplication(); err != nil {
+		return err
+	}
 	if err := this.validateBinlogs(); err != nil {
 		return err
 	}
@@ -69,7 +72,7 @@ func (this *Inspector) ValidateOriginalTable() (err error) {
 	return nil
 }
 
-func (this *Inspector) InspectTableColumnsAndUniqueKeys(tableName string) (columns sql.ColumnList, uniqueKeys [](*sql.UniqueKey), err error) {
+func (this *Inspector) InspectTableColumnsAndUniqueKeys(tableName string) (columns *sql.ColumnList, uniqueKeys [](*sql.UniqueKey), err error) {
 	uniqueKeys, err = this.getCandidateUniqueKeys(tableName)
 	if err != nil {
 		return columns, uniqueKeys, err
@@ -90,7 +93,6 @@ func (this *Inspector) InspectOriginalTable() (err error) {
 	if err == nil {
 		return err
 	}
-	this.migrationContext.OriginalTableColumnsMap = sql.NewColumnsMap(this.migrationContext.OriginalTableColumns)
 	return nil
 }
 
@@ -108,6 +110,11 @@ func (this *Inspector) InspectOriginalAndGhostTables() (err error) {
 	}
 	this.migrationContext.UniqueKey = sharedUniqueKeys[0]
 	log.Infof("Chosen shared unique key is %s", this.migrationContext.UniqueKey.Name)
+	if !this.migrationContext.UniqueKey.IsPrimary() {
+		if this.migrationContext.OriginalBinlogRowImage != "full" {
+			return fmt.Errorf("binlog_row_image is '%s' and chosen key is %s, which is not the primary key. This operation cannot proceed. You may `set global binlog_row_image='full'` and try again")
+		}
+	}
 
 	this.migrationContext.SharedColumns = this.getSharedColumns(this.migrationContext.OriginalTableColumns, this.migrationContext.GhostTableColumns)
 	log.Infof("Shared columns are %s", this.migrationContext.SharedColumns)
@@ -171,6 +178,26 @@ func (this *Inspector) validateGrants() error {
 	return log.Errorf("User has insufficient privileges for migration.")
 }
 
+// restartReplication is required so that we are _certain_ the binlog format and
+// row image settings have actually been applied to the replication thread.
+// It is entriely possible, for example, that the replication is using 'STATEMENT'
+// binlog format even as the variable says 'ROW'
+func (this *Inspector) restartReplication() error {
+	log.Infof("Restarting replication on %s:%d to make sure binlog settings apply to replication thread", this.connectionConfig.Key.Hostname, this.connectionConfig.Key.Port)
+
+	var stopError, startError error
+	_, stopError = sqlutils.ExecNoPrepare(this.db, `stop slave`)
+	_, startError = sqlutils.ExecNoPrepare(this.db, `start slave`)
+	if stopError != nil {
+		return stopError
+	}
+	if startError != nil {
+		return startError
+	}
+	log.Debugf("Replication restarted")
+	return nil
+}
+
 // validateBinlogs checks that binary log configuration is good to go
 func (this *Inspector) validateBinlogs() error {
 	query := `select @@global.log_bin, @@global.log_slave_updates, @@global.binlog_format`
@@ -299,27 +326,28 @@ func (this *Inspector) countTableRows() error {
 	return nil
 }
 
-func (this *Inspector) getTableColumns(databaseName, tableName string) (columns sql.ColumnList, err error) {
+func (this *Inspector) getTableColumns(databaseName, tableName string) (*sql.ColumnList, error) {
 	query := fmt.Sprintf(`
 		show columns from %s.%s
 		`,
 		sql.EscapeName(databaseName),
 		sql.EscapeName(tableName),
 	)
-	err = sqlutils.QueryRowsMap(this.db, query, func(rowMap sqlutils.RowMap) error {
+	columnNames := []string{}
-		columns = append(columns, rowMap.GetString("Field"))
+	err := sqlutils.QueryRowsMap(this.db, query, func(rowMap sqlutils.RowMap) error {
+		columnNames = append(columnNames, rowMap.GetString("Field"))
 		return nil
 	})
 	if err != nil {
-		return columns, err
+		return nil, err
 	}
-	if len(columns) == 0 {
+	if len(columnNames) == 0 {
-		return columns, log.Errorf("Found 0 columns on %s.%s. Bailing out",
+		return nil, log.Errorf("Found 0 columns on %s.%s. Bailing out",
 			sql.EscapeName(databaseName),
 			sql.EscapeName(tableName),
 		)
 	}
-	return columns, nil
+	return sql.NewColumnList(columnNames), nil
 }
 
 // getCandidateUniqueKeys investigates a table and returns the list of unique keys
@@ -412,17 +440,18 @@ func (this *Inspector) getSharedUniqueKeys(originalUniqueKeys, ghostUniqueKeys [
 }
 
 // getSharedColumns returns the intersection of two lists of columns in same order as the first list
-func (this *Inspector) getSharedColumns(originalColumns, ghostColumns sql.ColumnList) (sharedColumns sql.ColumnList) {
+func (this *Inspector) getSharedColumns(originalColumns, ghostColumns *sql.ColumnList) *sql.ColumnList {
 	columnsInGhost := make(map[string]bool)
-	for _, ghostColumn := range ghostColumns {
+	for _, ghostColumn := range ghostColumns.Names {
 		columnsInGhost[ghostColumn] = true
 	}
-	for _, originalColumn := range originalColumns {
+	sharedColumnNames := []string{}
+	for _, originalColumn := range originalColumns.Names {
 		if columnsInGhost[originalColumn] {
-			sharedColumns = append(sharedColumns, originalColumn)
+			sharedColumnNames = append(sharedColumnNames, originalColumn)
 		}
 	}
-	return sharedColumns
+	return sql.NewColumnList(sharedColumnNames)
 }
 
 func (this *Inspector) getMasterConnectionConfig() (masterConfig *mysql.ConnectionConfig, err error) {

go/logic/migrator.go

@@ -8,8 +8,10 @@ package logic
 import (
 	"fmt"
 	"os"
+	"os/signal"
 	"regexp"
 	"sync/atomic"
+	"syscall"
 	"time"
 
 	"github.com/github/gh-osc/go/base"
@@ -74,6 +76,21 @@ func prettifyDurationOutput(d time.Duration) string {
 	return result
 }
 
+// acceptSignals registers for OS signals
+func (this *Migrator) acceptSignals() {
+	c := make(chan os.Signal, 1)
+
+	signal.Notify(c, syscall.SIGHUP)
+	go func() {
+		for sig := range c {
+			switch sig {
+			case syscall.SIGHUP:
+				log.Debugf("Received SIGHUP. Reloading configuration")
+			}
+		}
+	}()
+}
+
 func (this *Migrator) shouldThrottle() (result bool, reason string) {
 	lag := atomic.LoadInt64(&this.migrationContext.CurrentLag)
 
@@ -82,7 +99,13 @@ func (this *Migrator) shouldThrottle() (result bool, reason string) {
 	}
 	if this.migrationContext.ThrottleFlagFile != "" {
 		if _, err := os.Stat(this.migrationContext.ThrottleFlagFile); err == nil {
-			//Throttle file defined and exists!
+			// Throttle file defined and exists!
+			return true, "flag-file"
+		}
+	}
+	if this.migrationContext.ThrottleAdditionalFlagFile != "" {
+		if _, err := os.Stat(this.migrationContext.ThrottleAdditionalFlagFile); err == nil {
+			// 2nd Throttle file defined and exists!
 			return true, "flag-file"
 		}
 	}
@@ -100,37 +123,43 @@ func (this *Migrator) shouldThrottle() (result bool, reason string) {
 	return false, ""
 }
 
+func (this *Migrator) initiateThrottler() error {
+	throttlerTick := time.Tick(1 * time.Second)
+
+	throttlerFunction := func() {
+		alreadyThrottling, currentReason := this.migrationContext.IsThrottled()
+		shouldThrottle, throttleReason := this.shouldThrottle()
+		if shouldThrottle && !alreadyThrottling {
+			// New throttling
+			this.applier.WriteAndLogChangelog("throttle", throttleReason)
+		} else if shouldThrottle && alreadyThrottling && (currentReason != throttleReason) {
+			// Change of reason
+			this.applier.WriteAndLogChangelog("throttle", throttleReason)
+		} else if alreadyThrottling && !shouldThrottle {
+			// End of throttling
+			this.applier.WriteAndLogChangelog("throttle", "done throttling")
+		}
+		this.migrationContext.SetThrottled(shouldThrottle, throttleReason)
+	}
+	throttlerFunction()
+	for range throttlerTick {
+		throttlerFunction()
+	}
+
+	return nil
+}
+
 // throttle initiates a throttling event, if need be, updates the Context and
 // calls callback functions, if any
-func (this *Migrator) throttle(
+func (this *Migrator) throttle(onThrottled func()) {
-	onStartThrottling func(),
-	onContinuousThrottling func(),
-	onEndThrottling func(),
-) {
-	hasThrottledYet := false
 	for {
-		shouldThrottle, reason := this.shouldThrottle()
+		if shouldThrottle, _ := this.migrationContext.IsThrottled(); !shouldThrottle {
-		if !shouldThrottle {
+			return
-			break
 		}
-		this.migrationContext.ThrottleReason = reason
+		if onThrottled != nil {
-		if !hasThrottledYet {
+			onThrottled()
-			hasThrottledYet = true
-			if onStartThrottling != nil {
-				onStartThrottling()
-			}
-			this.migrationContext.SetThrottled(true)
 		}
 		time.Sleep(time.Second)
-		if onContinuousThrottling != nil {
-			onContinuousThrottling()
-		}
-	}
-	if hasThrottledYet {
-		if onEndThrottling != nil {
-			onEndThrottling()
-		}
-		this.migrationContext.SetThrottled(false)
 	}
 }
 
@@ -239,6 +268,7 @@ func (this *Migrator) Migrate() (err error) {
 	if err := this.applier.ReadMigrationRangeValues(); err != nil {
 		return err
 	}
+	go this.initiateThrottler()
 	go this.executeWriteFuncs()
 	go this.iterateChunks()
 	this.migrationContext.RowCopyStartTime = time.Now()
@@ -249,15 +279,9 @@ func (this *Migrator) Migrate() (err error) {
 	log.Debugf("Row copy complete")
 	this.printStatus()
 
-	this.throttle(
+	this.throttle(func() {
-		func() {
+		log.Debugf("throttling on LOCK TABLES")
-			log.Debugf("throttling before LOCK TABLES")
+	})
-		},
-		nil,
-		func() {
-			log.Debugf("done throttling")
-		},
-	)
 	// TODO retries!!
 	this.applier.LockTables()
 	this.applier.WriteChangelogState(string(AllEventsUpToLockProcessed))
@@ -304,8 +328,8 @@ func (this *Migrator) printStatus() {
 	}
 
 	eta := "N/A"
-	if this.migrationContext.IsThrottled() {
+	if isThrottled, throttleReason := this.migrationContext.IsThrottled(); isThrottled {
-		eta = fmt.Sprintf("throttled, %s", this.migrationContext.ThrottleReason)
+		eta = fmt.Sprintf("throttled, %s", throttleReason)
 	}
 	status := fmt.Sprintf("Copy: %d/%d %.1f%%; Backlog: %d/%d; Elapsed: %+v(copy), %+v(total); ETA: %s",
 		totalRowsCopied, rowsEstimate, progressPct,
@@ -399,14 +423,8 @@ func (this *Migrator) iterateChunks() error {
 }
 
 func (this *Migrator) executeWriteFuncs() error {
-	onStartThrottling := func() {
-		log.Debugf("throttling writes")
-	}
-	onEndThrottling := func() {
-		log.Debugf("done throttling writes")
-	}
 	for {
-		this.throttle(onStartThrottling, nil, onEndThrottling)
+		this.throttle(nil)
 		// We give higher priority to event processing, then secondary priority to
 		// rowcopy
 		select {

go/sql/builder.go

@@ -32,6 +32,20 @@ func EscapeName(name string) string {
 	return fmt.Sprintf("`%s`", name)
 }
 
+func buildPreparedValues(length int) []string {
+	values := make([]string, length, length)
+	for i := 0; i < length; i++ {
+		values[i] = "?"
+	}
+	return values
+}
+
+func duplicateNames(names []string) []string {
+	duplicate := make([]string, len(names), len(names))
+	copy(duplicate, names)
+	return duplicate
+}
+
 func BuildValueComparison(column string, value string, comparisonSign ValueComparisonSign) (result string, err error) {
 	if column == "" {
 		return "", fmt.Errorf("Empty column in GetValueComparison")
@@ -64,6 +78,11 @@ func BuildEqualsComparison(columns []string, values []string) (result string, er
 	return result, nil
 }
 
+func BuildEqualsPreparedComparison(columns []string) (result string, err error) {
+	values := buildPreparedValues(len(columns))
+	return BuildEqualsComparison(columns, values)
+}
+
 func BuildRangeComparison(columns []string, values []string, args []interface{}, comparisonSign ValueComparisonSign) (result string, explodedArgs []interface{}, err error) {
 	if len(columns) == 0 {
 		return "", explodedArgs, fmt.Errorf("Got 0 columns in GetRangeComparison")
@@ -121,10 +140,7 @@ func BuildRangeComparison(columns []string, values []string, args []interface{},
 }
 
 func BuildRangePreparedComparison(columns []string, args []interface{}, comparisonSign ValueComparisonSign) (result string, explodedArgs []interface{}, err error) {
-	values := make([]string, len(columns), len(columns))
+	values := buildPreparedValues(len(columns))
-	for i := range columns {
-		values[i] = "?"
-	}
 	return BuildRangeComparison(columns, values, args, comparisonSign)
 }
 
@@ -135,6 +151,7 @@ func BuildRangeInsertQuery(databaseName, originalTableName, ghostTableName strin
 	databaseName = EscapeName(databaseName)
 	originalTableName = EscapeName(originalTableName)
 	ghostTableName = EscapeName(ghostTableName)
+	sharedColumns = duplicateNames(sharedColumns)
 	for i := range sharedColumns {
 		sharedColumns[i] = EscapeName(sharedColumns[i])
 	}
@@ -171,12 +188,8 @@ func BuildRangeInsertQuery(databaseName, originalTableName, ghostTableName strin
 }
 
 func BuildRangeInsertPreparedQuery(databaseName, originalTableName, ghostTableName string, sharedColumns []string, uniqueKey string, uniqueKeyColumns []string, rangeStartArgs, rangeEndArgs []interface{}, includeRangeStartValues bool, transactionalTable bool) (result string, explodedArgs []interface{}, err error) {
-	rangeStartValues := make([]string, len(uniqueKeyColumns), len(uniqueKeyColumns))
+	rangeStartValues := buildPreparedValues(len(uniqueKeyColumns))
-	rangeEndValues := make([]string, len(uniqueKeyColumns), len(uniqueKeyColumns))
+	rangeEndValues := buildPreparedValues(len(uniqueKeyColumns))
-	for i := range uniqueKeyColumns {
-		rangeStartValues[i] = "?"
-		rangeEndValues[i] = "?"
-	}
 	return BuildRangeInsertQuery(databaseName, originalTableName, ghostTableName, sharedColumns, uniqueKey, uniqueKeyColumns, rangeStartValues, rangeEndValues, rangeStartArgs, rangeEndArgs, includeRangeStartValues, transactionalTable)
 }
 
@@ -198,6 +211,7 @@ func BuildUniqueKeyRangeEndPreparedQuery(databaseName, tableName string, uniqueK
 	}
 	explodedArgs = append(explodedArgs, rangeExplodedArgs...)
 
+	uniqueKeyColumns = duplicateNames(uniqueKeyColumns)
 	uniqueKeyColumnAscending := make([]string, len(uniqueKeyColumns), len(uniqueKeyColumns))
 	uniqueKeyColumnDescending := make([]string, len(uniqueKeyColumns), len(uniqueKeyColumns))
 	for i := range uniqueKeyColumns {
@@ -244,6 +258,7 @@ func buildUniqueKeyMinMaxValuesPreparedQuery(databaseName, tableName string, uni
 	databaseName = EscapeName(databaseName)
 	tableName = EscapeName(tableName)
 
+	uniqueKeyColumns = duplicateNames(uniqueKeyColumns)
 	uniqueKeyColumnOrder := make([]string, len(uniqueKeyColumns), len(uniqueKeyColumns))
 	for i := range uniqueKeyColumns {
 		uniqueKeyColumns[i] = EscapeName(uniqueKeyColumns[i])
@@ -262,3 +277,65 @@ func buildUniqueKeyMinMaxValuesPreparedQuery(databaseName, tableName string, uni
 	)
 	return query, nil
 }
+
+func BuildDMLDeleteQuery(databaseName, tableName string, originalTableColumns, uniqueKeyColumns *ColumnList, args []interface{}) (result string, uniqueKeyArgs []interface{}, err error) {
+	if len(args) != originalTableColumns.Len() {
+		return result, uniqueKeyArgs, fmt.Errorf("args count differs from table column count in BuildDMLDeleteQuery")
+	}
+	for _, column := range uniqueKeyColumns.Names {
+		tableOrdinal := originalTableColumns.Ordinals[column]
+		uniqueKeyArgs = append(uniqueKeyArgs, args[tableOrdinal])
+	}
+	databaseName = EscapeName(databaseName)
+	tableName = EscapeName(tableName)
+	equalsComparison, err := BuildEqualsPreparedComparison(uniqueKeyColumns.Names)
+	result = fmt.Sprintf(`
+			delete /* gh-osc %s.%s */
+				from
+					%s.%s
+				where
+					%s
+		`, databaseName, tableName,
+		databaseName, tableName,
+		equalsComparison,
+	)
+	return result, uniqueKeyArgs, err
+}
+
+func BuildDMLInsertQuery(databaseName, tableName string, originalTableColumns, sharedColumns *ColumnList, args []interface{}) (result string, sharedArgs []interface{}, err error) {
+	if len(args) != originalTableColumns.Len() {
+		return result, args, fmt.Errorf("args count differs from table column count in BuildDMLInsertQuery")
+	}
+	if !sharedColumns.IsSubsetOf(originalTableColumns) {
+		return result, args, fmt.Errorf("shared columns is not a subset of table columns in BuildDMLInsertQuery")
+	}
+	if sharedColumns.Len() == 0 {
+		return result, args, fmt.Errorf("No shared columns found in BuildDMLInsertQuery")
+	}
+	databaseName = EscapeName(databaseName)
+	tableName = EscapeName(tableName)
+
+	for _, column := range sharedColumns.Names {
+		tableOrdinal := originalTableColumns.Ordinals[column]
+		sharedArgs = append(sharedArgs, args[tableOrdinal])
+	}
+
+	sharedColumnNames := duplicateNames(sharedColumns.Names)
+	for i := range sharedColumnNames {
+		sharedColumnNames[i] = EscapeName(sharedColumnNames[i])
+	}
+	preparedValues := buildPreparedValues(sharedColumns.Len())
+
+	result = fmt.Sprintf(`
+			replace /* gh-osc %s.%s */ into
+				%s.%s
+					(%s)
+				values
+					(%s)
+		`, databaseName, tableName,
+		databaseName, tableName,
+		strings.Join(sharedColumnNames, ", "),
+		strings.Join(preparedValues, ", "),
+	)
+	return result, sharedArgs, err
+}

go/sql/builder_test.go

@@ -68,6 +68,15 @@ func TestBuildEqualsComparison(t *testing.T) {
 	}
 }
 
+func TestBuildEqualsPreparedComparison(t *testing.T) {
+	{
+		columns := []string{"c1", "c2"}
+		comparison, err := BuildEqualsPreparedComparison(columns)
+		test.S(t).ExpectNil(err)
+		test.S(t).ExpectEquals(comparison, "((`c1` = ?) and (`c2` = ?))")
+	}
+}
+
 func TestBuildRangeComparison(t *testing.T) {
 	{
 		columns := []string{"c1"}
@@ -143,7 +152,7 @@ func TestBuildRangeInsertQuery(t *testing.T) {
 		rangeStartArgs := []interface{}{3}
 		rangeEndArgs := []interface{}{103}
 
-		query, explodedArgs, err := BuildRangeInsertQuery(databaseName, originalTableName, ghostTableName, sharedColumns, uniqueKey, uniqueKeyColumns, rangeStartValues, rangeEndValues, rangeStartArgs, rangeEndArgs, true)
+		query, explodedArgs, err := BuildRangeInsertQuery(databaseName, originalTableName, ghostTableName, sharedColumns, uniqueKey, uniqueKeyColumns, rangeStartValues, rangeEndValues, rangeStartArgs, rangeEndArgs, true, false)
 		test.S(t).ExpectNil(err)
 		expected := `
 				insert /* gh-osc mydb.tbl */ ignore into mydb.ghost (id, name, position)
@@ -162,7 +171,7 @@ func TestBuildRangeInsertQuery(t *testing.T) {
 		rangeStartArgs := []interface{}{3, 17}
 		rangeEndArgs := []interface{}{103, 117}
 
-		query, explodedArgs, err := BuildRangeInsertQuery(databaseName, originalTableName, ghostTableName, sharedColumns, uniqueKey, uniqueKeyColumns, rangeStartValues, rangeEndValues, rangeStartArgs, rangeEndArgs, true)
+		query, explodedArgs, err := BuildRangeInsertQuery(databaseName, originalTableName, ghostTableName, sharedColumns, uniqueKey, uniqueKeyColumns, rangeStartValues, rangeEndValues, rangeStartArgs, rangeEndArgs, true, false)
 		test.S(t).ExpectNil(err)
 		expected := `
 				insert /* gh-osc mydb.tbl */ ignore into mydb.ghost (id, name, position)
@@ -186,13 +195,13 @@ func TestBuildRangeInsertPreparedQuery(t *testing.T) {
 		rangeStartArgs := []interface{}{3, 17}
 		rangeEndArgs := []interface{}{103, 117}
 
-		query, explodedArgs, err := BuildRangeInsertPreparedQuery(databaseName, originalTableName, ghostTableName, sharedColumns, uniqueKey, uniqueKeyColumns, rangeStartArgs, rangeEndArgs, true)
+		query, explodedArgs, err := BuildRangeInsertPreparedQuery(databaseName, originalTableName, ghostTableName, sharedColumns, uniqueKey, uniqueKeyColumns, rangeStartArgs, rangeEndArgs, true, true)
 		test.S(t).ExpectNil(err)
 		expected := `
 				insert /* gh-osc mydb.tbl */ ignore into mydb.ghost (id, name, position)
 				(select id, name, position from mydb.tbl force index (name_position_uidx)
 				  where (((name > ?) or (((name = ?)) AND (position > ?)) or ((name = ?) and (position = ?))) and ((name < ?) or (((name = ?)) AND (position < ?)) or ((name = ?) and (position = ?))))
-				)
+				lock in share mode )
 		`
 		test.S(t).ExpectEquals(normalizeQuery(query), normalizeQuery(expected))
 		test.S(t).ExpectTrue(reflect.DeepEqual(explodedArgs, []interface{}{3, 3, 17, 3, 17, 103, 103, 117, 103, 117}))
@@ -202,7 +211,7 @@ func TestBuildRangeInsertPreparedQuery(t *testing.T) {
 func TestBuildUniqueKeyRangeEndPreparedQuery(t *testing.T) {
 	databaseName := "mydb"
 	originalTableName := "tbl"
-	chunkSize := 500
+	var chunkSize int64 = 500
 	{
 		uniqueKeyColumns := []string{"name", "position"}
 		rangeStartArgs := []interface{}{3, 17}
@@ -262,3 +271,107 @@ func TestBuildUniqueKeyMinValuesPreparedQuery(t *testing.T) {
 		test.S(t).ExpectEquals(normalizeQuery(query), normalizeQuery(expected))
 	}
 }
+
+func TestBuildDMLDeleteQuery(t *testing.T) {
+	databaseName := "mydb"
+	tableName := "tbl"
+	tableColumns := NewColumnList([]string{"id", "name", "rank", "position", "age"})
+	args := []interface{}{3, "testname", "first", 17, 23}
+	{
+		uniqueKeyColumns := NewColumnList([]string{"position"})
+
+		query, uniqueKeyArgs, err := BuildDMLDeleteQuery(databaseName, tableName, tableColumns, uniqueKeyColumns, args)
+		test.S(t).ExpectNil(err)
+		expected := `
+			delete /* gh-osc mydb.tbl */
+				from
+					mydb.tbl
+				where
+					((position = ?))
+		`
+		test.S(t).ExpectEquals(normalizeQuery(query), normalizeQuery(expected))
+		test.S(t).ExpectTrue(reflect.DeepEqual(uniqueKeyArgs, []interface{}{17}))
+	}
+	{
+		uniqueKeyColumns := NewColumnList([]string{"name", "position"})
+
+		query, uniqueKeyArgs, err := BuildDMLDeleteQuery(databaseName, tableName, tableColumns, uniqueKeyColumns, args)
+		test.S(t).ExpectNil(err)
+		expected := `
+			delete /* gh-osc mydb.tbl */
+				from
+					mydb.tbl
+				where
+					((name = ?) and (position = ?))
+		`
+		test.S(t).ExpectEquals(normalizeQuery(query), normalizeQuery(expected))
+		test.S(t).ExpectTrue(reflect.DeepEqual(uniqueKeyArgs, []interface{}{"testname", 17}))
+	}
+	{
+		uniqueKeyColumns := NewColumnList([]string{"position", "name"})
+
+		query, uniqueKeyArgs, err := BuildDMLDeleteQuery(databaseName, tableName, tableColumns, uniqueKeyColumns, args)
+		test.S(t).ExpectNil(err)
+		expected := `
+			delete /* gh-osc mydb.tbl */
+				from
+					mydb.tbl
+				where
+					((position = ?) and (name = ?))
+		`
+		test.S(t).ExpectEquals(normalizeQuery(query), normalizeQuery(expected))
+		test.S(t).ExpectTrue(reflect.DeepEqual(uniqueKeyArgs, []interface{}{17, "testname"}))
+	}
+	{
+		uniqueKeyColumns := NewColumnList([]string{"position", "name"})
+		args := []interface{}{"first", 17}
+
+		_, _, err := BuildDMLDeleteQuery(databaseName, tableName, tableColumns, uniqueKeyColumns, args)
+		test.S(t).ExpectNotNil(err)
+	}
+}
+
+func TestBuildDMLInsertQuery(t *testing.T) {
+	databaseName := "mydb"
+	tableName := "tbl"
+	tableColumns := NewColumnList([]string{"id", "name", "rank", "position", "age"})
+	args := []interface{}{3, "testname", "first", 17, 23}
+	{
+		sharedColumns := NewColumnList([]string{"id", "name", "position", "age"})
+		query, sharedArgs, err := BuildDMLInsertQuery(databaseName, tableName, tableColumns, sharedColumns, args)
+		test.S(t).ExpectNil(err)
+		expected := `
+			replace /* gh-osc mydb.tbl */
+				into mydb.tbl
+					(id, name, position, age)
+				values
+					(?, ?, ?, ?)
+		`
+		test.S(t).ExpectEquals(normalizeQuery(query), normalizeQuery(expected))
+		test.S(t).ExpectTrue(reflect.DeepEqual(sharedArgs, []interface{}{3, "testname", 17, 23}))
+	}
+	{
+		sharedColumns := NewColumnList([]string{"position", "name", "age", "id"})
+		query, sharedArgs, err := BuildDMLInsertQuery(databaseName, tableName, tableColumns, sharedColumns, args)
+		test.S(t).ExpectNil(err)
+		expected := `
+			replace /* gh-osc mydb.tbl */
+				into mydb.tbl
+					(position, name, age, id)
+				values
+					(?, ?, ?, ?)
+		`
+		test.S(t).ExpectEquals(normalizeQuery(query), normalizeQuery(expected))
+		test.S(t).ExpectTrue(reflect.DeepEqual(sharedArgs, []interface{}{17, "testname", 23, 3}))
+	}
+	{
+		sharedColumns := NewColumnList([]string{"position", "name", "surprise", "id"})
+		_, _, err := BuildDMLInsertQuery(databaseName, tableName, tableColumns, sharedColumns, args)
+		test.S(t).ExpectNotNil(err)
+	}
+	{
+		sharedColumns := NewColumnList([]string{})
+		_, _, err := BuildDMLInsertQuery(databaseName, tableName, tableColumns, sharedColumns, args)
+		test.S(t).ExpectNotNil(err)
+	}
+}

go/sql/types.go

@@ -11,34 +11,64 @@ import (
 	"strings"
 )
 
-// ColumnList makes for a named list of columns
-type ColumnList []string
-
-// ParseColumnList parses a comma delimited list of column names
-func ParseColumnList(columns string) *ColumnList {
-	result := ColumnList(strings.Split(columns, ","))
-	return &result
-}
-
-func (this *ColumnList) String() string {
-	return strings.Join(*this, ",")
-}
-
-func (this *ColumnList) Equals(other *ColumnList) bool {
-	return reflect.DeepEqual(*this, *other)
-}
-
 // ColumnsMap maps a column onto its ordinal position
 type ColumnsMap map[string]int
 
-func NewColumnsMap(columnList ColumnList) ColumnsMap {
+func NewColumnsMap(orderedNames []string) ColumnsMap {
 	columnsMap := make(map[string]int)
-	for i, column := range columnList {
+	for i, column := range orderedNames {
 		columnsMap[column] = i
 	}
 	return ColumnsMap(columnsMap)
 }
 
+// ColumnList makes for a named list of columns
+type ColumnList struct {
+	Names    []string
+	Ordinals ColumnsMap
+}
+
+// NewColumnList creates an object given ordered list of column names
+func NewColumnList(names []string) *ColumnList {
+	result := &ColumnList{
+		Names: names,
+	}
+	result.Ordinals = NewColumnsMap(result.Names)
+	return result
+}
+
+// ParseColumnList parses a comma delimited list of column names
+func ParseColumnList(columns string) *ColumnList {
+	result := &ColumnList{
+		Names: strings.Split(columns, ","),
+	}
+	result.Ordinals = NewColumnsMap(result.Names)
+	return result
+}
+
+func (this *ColumnList) String() string {
+	return strings.Join(this.Names, ",")
+}
+
+func (this *ColumnList) Equals(other *ColumnList) bool {
+	return reflect.DeepEqual(this.Names, other.Names)
+}
+
+// IsSubsetOf returns 'true' when column names of this list are a subset of
+// another list, in arbitrary order (order agnostic)
+func (this *ColumnList) IsSubsetOf(other *ColumnList) bool {
+	for _, column := range this.Names {
+		if _, exists := other.Ordinals[column]; !exists {
+			return false
+		}
+	}
+	return true
+}
+
+func (this *ColumnList) Len() int {
+	return len(this.Names)
+}
+
 // UniqueKey is the combination of a key's name and columns
 type UniqueKey struct {
 	Name        string
@@ -51,6 +81,10 @@ func (this *UniqueKey) IsPrimary() bool {
 	return this.Name == "PRIMARY"
 }
 
+func (this *UniqueKey) Len() int {
+	return this.Columns.Len()
+}
+
 func (this *UniqueKey) String() string {
 	return fmt.Sprintf("%s: %s; has nullable: %+v", this.Name, this.Columns, this.HasNullable)
 }