Re: FDW system columns

On 13 November 2011 00:38, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Thom Brown <thom(at)linux(dot)com> writes:
>> But xmin on the file_fdw result is odd.  Why are these all over the
>> place?
>
> heap_form_tuple initializes the t_choice fields as though for a tuple
> Datum, and file_fdw doesn't change it.
>
> Just a couple hours ago I was wondering why we create system columns for
> foreign tables at all.  Is there a reasonable prospect that they'll ever
> be useful?  I can see potential value in tableoid, but the others seem
> pretty dubious --- even if you were fetching from a remote PG server,
> the XIDs would not be meaningful within our own environment.

Yes, that's what I was thinking when curiosity led me to have a look
at what they contain. As far as I see, they serve no useful function.
I didn't bother looking at tableoid as that's generally useful.

Is there a cost to having them there? Could there be tools that might
break if the columns were no longer available?

--
Thom Brown
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