[8.0] OnlineDDL bugfix: make sure schema is applied on tablet

go/mysql/constants.go

@@ -579,3 +579,20 @@ func IsConnErr(err error) bool {
 	}
 	return false
 }
+
+// IsSchemaApplyError returns true when given error is a MySQL error applying schema change
+func IsSchemaApplyError(err error) bool {
+	merr, isSQLErr := err.(*SQLError)
+	if !isSQLErr {
+		return false
+	}
+	switch merr.Num {
+	case
+		ERDupKeyName,
+		ERCantDropFieldOrKey,
+		ERTableExists,
+		ERDupFieldName:
+		return true
+	}
+	return false
+}

go/vt/vttablet/onlineddl/executor.go

@@ -32,6 +32,7 @@ import (
 	"syscall"
 	"time"
 
+	"vitess.io/vitess/go/mysql"
 	"vitess.io/vitess/go/sqltypes"
 	"vitess.io/vitess/go/textutil"
 	"vitess.io/vitess/go/timer"
@@ -119,8 +120,9 @@ type Executor struct {
 	migrationRunning  int64
 	lastMigrationUUID string
 
-	ticks  *timer.Timer
-	isOpen bool
+	ticks             *timer.Timer
+	isOpen            bool
+	schemaInitialized bool
 }
 
 // GhostBinaryFileName returns the full path+name of the gh-ost binary
@@ -167,16 +169,32 @@ func (e *Executor) execQuery(ctx context.Context, query string) (result *sqltype
 }
 
 func (e *Executor) initSchema(ctx context.Context) error {
+	e.initMutex.Lock()
+	defer e.initMutex.Unlock()
+
+	if e.schemaInitialized {
+		return nil
+	}
+
 	defer e.env.LogError()
 
 	conn, err := e.pool.Get(ctx)
 	if err != nil {
 		return err
 	}
 	defer conn.Recycle()
-	parsed := sqlparser.BuildParsedQuery(sqlValidationQuery, "_vt")
-	_, err = withDDL.Exec(ctx, parsed.Query, conn.Exec)
-	return err
+
+	for _, ddl := range applyDDL {
+		_, err := conn.Exec(ctx, ddl, math.MaxInt32, false)
+		if mysql.IsSchemaApplyError(err) {
+			continue
+		}
+		if err != nil {
+			return err
+		}
+	}
+	e.schemaInitialized = true
+	return nil
 }
 
 // InitDBConfig initializes keysapce
@@ -194,7 +212,6 @@ func (e *Executor) Open() error {
 		return nil
 	}
 	e.pool.Open(e.env.Config().DB.AppWithDB(), e.env.Config().DB.DbaWithDB(), e.env.Config().DB.AppDebugWithDB())
-	e.initSchema(context.Background())
 	e.ticks.Start(e.onMigrationCheckTick)
 
 	if _, err := sqlparser.QueryMatchesTemplates("select 1 from dual", vexecUpdateTemplates); err != nil {
@@ -1140,6 +1157,10 @@ func (e *Executor) onMigrationCheckTick() {
 	}
 	ctx := context.Background()
 
+	if err := e.initSchema(ctx); err != nil {
+		log.Error(err)
+		return
+	}
 	if err := e.scheduleNextMigration(ctx); err != nil {
 		log.Error(err)
 	}

go/vt/vttablet/onlineddl/schema.go

@@ -18,8 +18,6 @@ package onlineddl
 
 import (
 	"fmt"
-
-	"vitess.io/vitess/go/vt/withddl"
 )
 
 const (
@@ -52,7 +50,6 @@ const (
 		KEY status_idx (migration_status, liveness_timestamp),
 		KEY cleanup_status_idx (cleanup_timestamp, migration_status)
 	) engine=InnoDB DEFAULT CHARSET=utf8mb4`
-	sqlValidationQuery         = `select 1 from %s.schema_migrations limit 1`
 	sqlScheduleSingleMigration = `UPDATE %s.schema_migrations
 		SET
 			migration_status='ready',
@@ -201,7 +198,7 @@ var (
 	sqlDropOnlineDDLUser = `DROP USER IF EXISTS %s`
 )
 
-var withDDL = withddl.New([]string{
+var applyDDL = []string{
 	fmt.Sprintf(sqlCreateSidecarDB, "_vt"),
 	fmt.Sprintf(sqlCreateSchemaMigrationsTable, "_vt"),
-})
+}