SparkSQL overwrite parquet file does not generate _common_metadata

[Pei-Lun Lee]

Hi,

When I save parquet file with SaveMode.Overwrite, it never generate
_common_metadata. Whether it overwrites an existing dir or not.
Is this expected behavior?
And what is the benefit of _common_metadata? Will reading performs better
when it is present?

Thanks,
--
Pei-Lun