From: Tom Lane <tgl@sss.pgh.pa.us>
To: Andres Freund <andres@anarazel.de>
cc: Amit Langote <amitlangote09@gmail.com>,
 David Steele <david@pgmasters.net>,
        Pavel Biryukov <79166341370@yandex.ru>,
        PostgreSQL mailing lists <pgsql-bugs@lists.postgresql.org>
Subject: Re: posgres 12 bug (partitioned table)
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Comments: In-reply-to Andres Freund <andres@anarazel.de>
	message dated "Thu, 22 Apr 2021 11:57:24 -0700"
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Date: Thu, 22 Apr 2021 15:09:59 -0400
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Andres Freund <andres@anarazel.de> writes:
> On 2021-04-22 14:37:26 -0400, Tom Lane wrote:
>> OK, I could work with that.  Shall we spell the error message the
>> same as if it really were a virtual slot, or does it need to be
>> different to avoid confusion?

> Hm. Seems like it'd be better to have a distinct error message? Feels
> like it'll often indicate separate issues whether a non-materialized
> heap slot or a virtual slot has its system columns accessed.

After thinking about it for a bit, I'm inclined to promote this to
a user-facing error, and have all the slot types report

	ereport(ERROR,
	        (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
	         errmsg("cannot retrieve a system column in this context")));

which is at least somewhat intelligible to end users.  A developer
trying to figure out why it happened would resort to \errverbose or
more likely gdb in any case, so the lack of specificity doesn't
seem like a problem.

> Not entirely clear to me how we'd track whether we have valid system
> column data or not once materialized - which I think is why we
> historically had the cases where we returned bogus values.

Right, but with this fix we won't need to materialize.

			regards, tom lane