From: Tom Lane <tgl@sss.pgh.pa.us>
To: Peter Eisentraut <peter.eisentraut@enterprisedb.com>
cc: David Rowley <dgrowleyml@gmail.com>, sait.nisanci@microsoft.com,
        PostgreSQL mailing lists <pgsql-bugs@lists.postgresql.org>
Subject: Re: BUG #17158: Distinct ROW fails with Postgres 14
In-reply-to: <c182f5c8-fdf3-80a0-fa43-4ed7e87d4d47@enterprisedb.com>
References: <17158-8a2ba823982537a4@postgresql.org>
 <CAApHDvp0w_5YY=7pxPkymtv7Oc0cGS=+jtiBvXrfcM6gLjT5Pg@mail.gmail.com>
 <bc0ec85a-68cf-1b99-e80c-ee0c55b936db@enterprisedb.com>
 <496046.1629843371@sss.pgh.pa.us>
 <c182f5c8-fdf3-80a0-fa43-4ed7e87d4d47@enterprisedb.com>
Comments: In-reply-to Peter Eisentraut <peter.eisentraut@enterprisedb.com>
	message dated "Fri, 27 Aug 2021 12:36:04 +0200"
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-ID: <2021951.1630442634.1@sss.pgh.pa.us>
Date: Tue, 31 Aug 2021 16:43:54 -0400
Message-ID: <2021952.1630442634@sss.pgh.pa.us>
Archived-At: 
 <https://www.postgresql.org/message-id/2021952.1630442634%40sss.pgh.pa.us>
Precedence: bulk

Peter Eisentraut <peter.eisentraut@enterprisedb.com> writes:
> This feature is a requirement for multicolumn path and cycle tracking in 
> recursive queries, as well as the search/cycle syntax built on top of 
> that, so there is a bit more depending on it than might be at first 
> apparent.

Hmm.

> Variant 1 is that we let the type cache *not* report hash support for 
> the record type, and let callers fill it in.  In the attached patch I've 
> only done this for hash_array(), because that's what's needed to get the 
> tests to pass, but similar code would be possible for row types, range 
> types, etc.

> Variant 2 is that we let the type cache report hash support for the 
> record type, like now, and then let callers override it if they have 
> other options.  This is the second attached patch.

I find variant 1 a bit cleaner, and safer.  I'd rather default to
assuming that RECORD doesn't hash, when we don't have enough info
to be sure.

			regards, tom lane