Tom Lane <tgl@sss.pgh.pa.us> writes：
> I do not think this is a great idea. We don't use the tupdesc today
> perhaps, but it's plausible that it'd be needed in the future.
> Different table AMs might have different sets of system columns.
Thank you for your guidance.I didn't consider that different table AMs
might store system column information in tupdesc before.
