On Nov13, 2011, at 01:38 , Tom Lane wrote:
> 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.

At least ctid seems useful too. I've used that in the past as a poor man's
surrogate primary key.

Also, people have used ctid and xmin in the past to re-find previously
visited rows and to check whether they've been modified. So there might be
some value in keeping xmin around also (and make the postgres fdw populate it)

best regards,
Florian Pflug

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