Use multiStatement to apply DML

go/logic/applier.go

@@ -14,10 +14,13 @@ import (
 
 	"github.com/github/gh-ost/go/base"
 	"github.com/github/gh-ost/go/binlog"
-	"github.com/github/gh-ost/go/mysql"
 	"github.com/github/gh-ost/go/sql"
 
-	"github.com/openark/golib/log"
+	"context"
+	"database/sql/driver"
+
+	"github.com/github/gh-ost/go/mysql"
+	drivermysql "github.com/go-sql-driver/mysql"
 	"github.com/openark/golib/sqlutils"
 )
 
@@ -77,7 +80,8 @@ func NewApplier(migrationContext *base.MigrationContext) *Applier {
 
 func (this *Applier) InitDBConnections() (err error) {
 	applierUri := this.connectionConfig.GetDBUri(this.migrationContext.DatabaseName)
-	if this.db, _, err = mysql.GetDB(this.migrationContext.Uuid, applierUri); err != nil {
+	uriWithMulti := fmt.Sprintf("%s&multiStatements=true", applierUri)
+	if this.db, _, err = mysql.GetDB(this.migrationContext.Uuid, uriWithMulti); err != nil {
 		return err
 	}
 	singletonApplierUri := fmt.Sprintf("%s&timeout=0", applierUri)
@@ -1207,44 +1211,80 @@ func (this *Applier) buildDMLEventQuery(dmlEvent *binlog.BinlogDMLEvent) []*dmlB
 // ApplyDMLEventQueries applies multiple DML queries onto the _ghost_ table
 func (this *Applier) ApplyDMLEventQueries(dmlEvents [](*binlog.BinlogDMLEvent)) error {
 	var totalDelta int64
+	ctx := context.Background()
 
 	err := func() error {
-		tx, err := this.db.Begin()
+		conn, err := this.db.Conn(ctx)
 		if err != nil {
 			return err
 		}
+		defer conn.Close()
+
+		sessionQuery := "SET /* gh-ost */ SESSION time_zone = '+00:00'"
+		sessionQuery = fmt.Sprintf("%s, %s", sessionQuery, this.generateSqlModeQuery())
+		if _, err := conn.ExecContext(ctx, sessionQuery); err != nil {
+			return err
+		}
 
+		tx, err := conn.BeginTx(ctx, nil)
+		if err != nil {
+			return err
+		}
 		rollback := func(err error) error {
 			tx.Rollback()
 			return err
 		}
 
-		sessionQuery := "SET /* gh-ost */ SESSION time_zone = '+00:00'"
-		sessionQuery = fmt.Sprintf("%s, %s", sessionQuery, this.generateSqlModeQuery())
-
-		if _, err := tx.Exec(sessionQuery); err != nil {
-			return rollback(err)
-		}
+		buildResults := make([]*dmlBuildResult, 0, len(dmlEvents))
+		nArgs := 0
 		for _, dmlEvent := range dmlEvents {
 			for _, buildResult := range this.buildDMLEventQuery(dmlEvent) {
 				if buildResult.err != nil {
 					return rollback(buildResult.err)
 				}
-				result, err := tx.Exec(buildResult.query, buildResult.args...)
-				if err != nil {
-					err = fmt.Errorf("%w; query=%s; args=%+v", err, buildResult.query, buildResult.args)
-					return rollback(err)
-				}
+				nArgs += len(buildResult.args)
+				buildResults = append(buildResults, buildResult)
+			}
+		}
 
-				rowsAffected, err := result.RowsAffected()
-				if err != nil {
-					log.Warningf("error getting rows affected from DML event query: %s. i'm going to assume that the DML affected a single row, but this may result in inaccurate statistics", err)
-					rowsAffected = 1
+		// We batch together the DML queries into multi-statements to minimize network trips.
+		// We have to use the raw driver connection to access the rows affected
+		// for each statement in the multi-statement.
+		execErr := conn.Raw(func(driverConn any) error {
+			ex := driverConn.(driver.ExecerContext)
+			nvc := driverConn.(driver.NamedValueChecker)
+
+			multiArgs := make([]driver.NamedValue, 0, nArgs)
+			multiQueryBuilder := strings.Builder{}
+			for _, buildResult := range buildResults {
+				for _, arg := range buildResult.args {
+					nv := driver.NamedValue{Value: driver.Value(arg)}
+					nvc.CheckNamedValue(&nv)
+					multiArgs = append(multiArgs, nv)
 				}
-				// each DML is either a single insert (delta +1), update (delta +0) or delete (delta -1).
-				// multiplying by the rows actually affected (either 0 or 1) will give an accurate row delta for this DML event
-				totalDelta += buildResult.rowsDelta * rowsAffected
+
+				multiQueryBuilder.WriteString(buildResult.query)
+				multiQueryBuilder.WriteString(";\n")
 			}
+
+			res, err := ex.ExecContext(ctx, multiQueryBuilder.String(), multiArgs)
+			if err != nil {
+				err = fmt.Errorf("%w; query=%s; args=%+v", err, multiQueryBuilder.String(), multiArgs)
+				return err
+			}
+
+			mysqlRes := res.(drivermysql.Result)
+
+			// each DML is either a single insert (delta +1), update (delta +0) or delete (delta -1).
+			// multiplying by the rows actually affected (either 0 or 1) will give an accurate row delta for this DML event
+			for i, rowsAffected := range mysqlRes.AllRowsAffected() {
+				totalDelta += buildResults[i].rowsDelta * rowsAffected
+			}
+			return nil
+		})
+
+		if execErr != nil {
+			return rollback(execErr)
 		}
 		if err := tx.Commit(); err != nil {
 			return err