Re: FDW system columns

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Thom Brown <thom(at)linux(dot)com>
Cc: PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: FDW system columns
Date: 2011-11-13 00:38:10
Message-ID: 22453.1321144690@sss.pgh.pa.us
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Thom Brown <thom(at)linux(dot)com> writes:
> So the ctid is always 2^32-1. Bit weird, but probably explainable.

See ItemPointerSetInvalid.

> 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.

regards, tom lane

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