Added catchup mechanism and BinlogReconciler

binlog_reconciler.go

@@ -0,0 +1,223 @@
+package ghostferry
+
+import (
+	"database/sql"
+	"fmt"
+	"strings"
+
+	"github.com/Masterminds/squirrel"
+	"github.com/siddontang/go-mysql/schema"
+	"github.com/sirupsen/logrus"
+)
+
+// This event generates a REPLACE INTO SQL statement to overwrite a row if an
+// INSERT or UPDATE occured. For a DELETE statement, it generates the
+// corresponding DELETE statement based on the primary key.
+//
+// This is used during the resume when we are catching up to the binlog events
+// missed by Ghostferry while it is down.
+type ReconcilationDMLEvent struct {
+	*DMLEventBase
+	newValues RowData
+	pk        uint64
+}
+
+func (e *ReconcilationDMLEvent) OldValues() RowData {
+	return nil
+}
+
+func (e *ReconcilationDMLEvent) NewValues() RowData {
+	return e.newValues
+}
+
+func (e *ReconcilationDMLEvent) PK() (uint64, error) {
+	return e.pk, nil
+}
+
+func (e *ReconcilationDMLEvent) AsSQLString(target *schema.Table) (string, error) {
+	var query string
+	if e.newValues != nil {
+		columns, err := loadColumnsForTable(&e.table, e.newValues)
+		if err != nil {
+			return "", err
+		}
+
+		query = "REPLACE INTO " +
+			QuotedTableNameFromString(target.Schema, target.Name) +
+			" (" + strings.Join(columns, ",") + ")" +
+			" VALUES (" + buildStringListForValues(e.newValues) + ")"
+	} else {
+		pkColumnName := e.TableSchema().GetPKColumn(0).Name
+		if pkColumnName == "" {
+			return "", fmt.Errorf("cannot get PK column for table %s", e.Table())
+		}
+
+		pkColumnName = quoteField(pkColumnName)
+		query = "DELETE FROM " + QuotedTableNameFromString(target.Schema, target.Name) +
+			" WHERE " + buildStringMapForWhere([]string{pkColumnName}, []interface{}{e.pk})
+	}
+
+	return query, nil
+}
+
+func NewReconciliationDMLEvent(table *schema.Table, pk uint64, row RowData) DMLEvent {
+	return &ReconcilationDMLEvent{
+		DMLEventBase: &DMLEventBase{table: *table},
+		pk:           pk,
+		newValues:    row,
+	}
+}
+
+// Instead of replacing/deleting every row, we first store all the rows changed
+// during the downtime and perform all the operations at the end. This maybe
+// faster (trading memory usage tho) and it is crucial for schema changes (as
+// we can simply delete a key from this map when we realize a table has
+// changed).
+type UniqueRowMap map[TableIdentifier]map[uint64]struct{}
+
+func (m UniqueRowMap) AddRow(table *schema.Table, pk uint64) bool {
+	tableId := NewTableIdentifierFromSchemaTable(table)
+	if _, exists := m[tableId]; !exists {
+		m[tableId] = make(map[uint64]struct{})
+	}
+
+	if _, exists := m[tableId][pk]; !exists {
+		m[tableId][pk] = struct{}{}
+		return true
+	}
+
+	return false
+}
+
+type BinlogReconciler struct {
+	BatchSize        int
+	TableSchemaCache TableSchemaCache
+
+	SourceDB     *sql.DB
+	BinlogWriter *BinlogWriter
+
+	modifiedRows UniqueRowMap
+	logger       *logrus.Entry
+}
+
+func (r *BinlogReconciler) Initialize() {
+	r.modifiedRows = make(UniqueRowMap)
+	r.logger = logrus.WithField("tag", "binlogreconcile")
+}
+
+func (r *BinlogReconciler) AddRowsToStore(events []DMLEvent) error {
+	for _, ev := range events {
+		pk, err := ev.PK()
+		if err != nil {
+			return err
+		}
+
+		r.modifiedRows.AddRow(ev.TableSchema(), pk)
+	}
+
+	return nil
+}
+
+func (r *BinlogReconciler) ReplaceModifiedRowsAfterCatchup() error {
+	batch := make([]DMLEvent, 0, r.BatchSize)
+
+	totalModifiedRows := 0
+	for _, pkSet := range r.modifiedRows {
+		totalModifiedRows += len(pkSet)
+	}
+
+	r.logger.WithField("row_count", totalModifiedRows).Info("begin replacing modified rows")
+
+	count := 0
+	for tableId, pkSet := range r.modifiedRows {
+		table := r.TableSchemaCache.Get(tableId.SchemaName, tableId.TableName)
+
+		for pk, _ := range pkSet {
+			count++
+
+			if len(batch) == r.BatchSize {
+				r.logger.WithField("rows_replaced", count).Debug("replacing batch")
+				err := r.replaceBatch(batch)
+				if err != nil {
+					return err
+				}
+
+				batch = make([]DMLEvent, 0, r.BatchSize)
+			}
+
+			row, err := r.selectRowFromSource(table, pk)
+			if err != nil {
+				r.logger.WithError(err).Error("failed to select row from source")
+				return err
+			}
+
+			batch = append(batch, NewReconciliationDMLEvent(table, pk, row))
+		}
+	}
+
+	if len(batch) > 0 {
+		err := r.replaceBatch(batch)
+		if err != nil {
+			return err
+		}
+	}
+
+	r.logger.WithField("row_count", totalModifiedRows).Info("replaced modified rows")
+
+	return nil
+}
+
+func (r *BinlogReconciler) replaceBatch(batch []DMLEvent) error {
+	err := r.BinlogWriter.WriteEvents(batch)
+	if err != nil {
+		r.logger.WithError(err).Error("cannot replace batch")
+		return err
+	}
+
+	return nil
+}
+
+func (r *BinlogReconciler) selectRowFromSource(table *schema.Table, pk uint64) (RowData, error) {
+	quotedPK := quoteField(table.GetPKColumn(0).Name)
+
+	query, args, err := squirrel.
+		Select("*").
+		From(QuotedTableName(table)).
+		Where(squirrel.Eq{quotedPK: pk}).ToSql()
+
+	if err != nil {
+		return nil, err
+	}
+
+	// TODO: make this cached for faster reconciliation
+	stmt, err := r.SourceDB.Prepare(query)
+	if err != nil {
+		return nil, err
+	}
+
+	defer stmt.Close()
+
+	rows, err := stmt.Query(args...)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+
+	var rowData RowData = nil
+	count := 0
+
+	for rows.Next() {
+		rowData, err = ScanGenericRow(rows, len(table.Columns))
+		if err != nil {
+			return nil, err
+		}
+
+		count++
+	}
+
+	if count > 1 {
+		return nil, fmt.Errorf("multiple rows detected when only one or zero is expected for %s %v", table.String(), pk)
+	}
+
+	return rowData, rows.Err()
+}

binlog_streamer.go

@@ -200,6 +200,11 @@ func (s *BinlogStreamer) IsAlmostCaughtUp() bool {
 	return time.Now().Sub(s.lastProcessedEventTime) < caughtUpThreshold
 }
 
+func (s *BinlogStreamer) FlushToTargetBinlogPositionAndStop(target mysql.Position) {
+	s.targetBinlogPosition = target
+	s.stopRequested = true
+}
+
 func (s *BinlogStreamer) FlushAndStop() {
 	s.logger.Info("requesting binlog streamer to stop")
 	// Must first read the binlog position before requesting stop

binlog_writer.go

@@ -53,7 +53,7 @@ func (b *BinlogWriter) Run() {
 		}
 
 		err := WithRetries(b.WriteRetries, 0, b.logger, "write events to target", func() error {
-			return b.writeEvents(batch)
+			return b.WriteEvents(batch)
 		})
 		if err != nil {
 			b.ErrorHandler.Fatal("binlog_writer", err)
@@ -75,7 +75,7 @@ func (b *BinlogWriter) BufferBinlogEvents(events []DMLEvent) error {
 	return nil
 }
 
-func (b *BinlogWriter) writeEvents(events []DMLEvent) error {
+func (b *BinlogWriter) WriteEvents(events []DMLEvent) error {
 	WaitForThrottle(b.Throttler)
 
 	queryBuffer := []byte("BEGIN;\n")

ferry.go

@@ -292,6 +292,102 @@ func (f *Ferry) Initialize() (err error) {
 	return nil
 }
 
+func (f *Ferry) CatchUpOnMissedBinlogsOnResume() error {
+	if f.StateToResumeFrom == nil {
+		return nil
+	}
+
+	tableSchemaCache := f.StateToResumeFrom.LastKnownTableSchemaCache
+
+	// Step 1: setup the binlog reconciler
+	binlogReconciler := &BinlogReconciler{
+		BatchSize:        f.Config.BinlogEventBatchSize,
+		TableSchemaCache: tableSchemaCache,
+
+		SourceDB:     f.SourceDB,
+		BinlogWriter: f.BinlogWriter,
+	}
+	binlogReconciler.Initialize()
+
+	// TODO: Step 2: setup the iterative verifier reconciler
+
+	// Step 3: initialize the binlog streamer and the throttler
+	binlogStreamer := f.NewBinlogStreamer()
+	binlogStreamer.TableSchema = tableSchemaCache
+
+	// Step 4: attach the reconcilers' binlog event listeners
+	binlogStreamer.AddEventListener(binlogReconciler.AddRowsToStore)
+	// TODO: attach the iterative verifier reconciler binlog listener
+
+	// Step 5: Connect the binlog streamer from the resuming coordinate
+	binlogStreamer.ConnectBinlogStreamerToMysqlFrom(f.StateToResumeFrom.LastWrittenBinlogPosition)
+
+	// Step 6: Start the throttler
+	ctx, shutdown := context.WithCancel(context.Background())
+	throttlerWg := &sync.WaitGroup{}
+	throttlerWg.Add(1)
+	go func() {
+		defer throttlerWg.Done()
+
+		err := f.Throttler.Run(ctx)
+		if err != nil {
+			f.ErrorHandler.Fatal("throttler", err)
+		}
+	}()
+	defer func() {
+		shutdown()
+		throttlerWg.Wait()
+	}()
+
+	// Step 7: run the binlog streamer until the current position
+	currentBinlogPos, err := ShowMasterStatusBinlogPosition(f.SourceDB)
+	if err != nil {
+		return err
+	}
+
+	f.logger.WithFields(logrus.Fields{
+		"from": f.StateToResumeFrom.LastWrittenBinlogPosition,
+		"to":   currentBinlogPos,
+	}).Info("catching up binlogs")
+
+	wg := &sync.WaitGroup{}
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		binlogStreamer.Run()
+	}()
+
+	binlogStreamer.FlushToTargetBinlogPositionAndStop(currentBinlogPos)
+	wg.Wait()
+
+	f.logger.WithFields(logrus.Fields{
+		"streamed_pos": binlogStreamer.GetLastStreamedBinlogPosition(),
+		"target_pos":   currentBinlogPos,
+	}).Info("binlog catch up completed")
+
+	// defensive programming
+	if binlogStreamer.GetLastStreamedBinlogPosition().Compare(currentBinlogPos) < 0 {
+		return fmt.Errorf("programming error: last streamed position %v is less than target position %v?", binlogStreamer.GetLastStreamedBinlogPosition(), currentBinlogPos)
+	}
+
+	// Step 8: REPLACE rows that have been modified
+	err = binlogReconciler.ReplaceModifiedRowsAfterCatchup()
+	if err != nil {
+		f.logger.WithError(err).Error("failed to replace modified rows")
+		return err
+	}
+
+	// TODO: Step 9: perform iterative verifier catchups
+
+	// Step 10: update the state to resume from so the rest of Ferry can pretend
+	// as if it was interrupted at currentBinlogPos as this method took care of
+	// all possible issues (including schema changes, although this is TODO).
+	f.StateToResumeFrom.LastWrittenBinlogPosition = currentBinlogPos
+	f.StateTracker.UpdateLastWrittenBinlogPosition(currentBinlogPos)
+
+	return nil
+}
+
 // Determine the binlog coordinates, table mapping for the pending
 // Ghostferry run.
 func (f *Ferry) Start() error {