diff --git a/internal/storage/data_codec.go b/internal/storage/data_codec.go
index 4186c8875b..63881499aa 100644
--- a/internal/storage/data_codec.go
+++ b/internal/storage/data_codec.go
@@ -105,6 +105,7 @@ func (b Blob) GetValue() []byte {
 	return b.Value
 }
 
+// FieldData defines field data interface
 type FieldData interface {
 	GetMemorySize() int
 	RowNum() int