diff --git a/pkg/types/field_name.go b/pkg/types/field_name.go
index 74f90607a7a13..dcd1fef048de3 100644
--- a/pkg/types/field_name.go
+++ b/pkg/types/field_name.go
@@ -15,7 +15,7 @@
 package types
 
 import (
-	"strings"
+	"bytes"
 
 	"github.com/pingcap/tidb/pkg/parser/ast"
 	"github.com/pingcap/tidb/pkg/util/size"
@@ -43,10 +43,11 @@ const emptyName = "EMPTY_NAME"
 
 // String implements Stringer interface.
 func (name *FieldName) String() string {
-	builder := strings.Builder{}
 	if name.Hidden {
 		return emptyName
 	}
+	bs := make([]byte, 0, len(name.DBName.L)+1+len(name.TblName.L)+1+len(name.ColName.L))
+	builder := bytes.NewBuffer(bs)
 	if name.DBName.L != "" {
 		builder.WriteString(name.DBName.L + ".")
 	}