From: Tom Lane <tgl@sss.pgh.pa.us>
To: David Rowley <dgrowleyml@gmail.com>
cc: Andres Freund <andres@anarazel.de>, xinwen@stu.scu.edu.cn,
        pgsql-bugs@lists.postgresql.org
Subject: Re: BUG #17777: An assert failed in nodeWindowAgg.c
In-reply-to: 
 <CAApHDvrfuSuFq57EtbYxHNWYhMET9K_TpSefDUoM52-T6LCYbg@mail.gmail.com>
References: <17777-860b739b6efde977@postgresql.org>
 <20230210230230.scuk6gqrks6c7sc7@awork3.anarazel.de>
 <439391.1676070752@sss.pgh.pa.us>
 <20230210232051.efjhtoqo6odk3gke@awork3.anarazel.de>
 <443909.1676073430@sss.pgh.pa.us>
 <20230211004940.t5l2dz7rnss76zao@awork3.anarazel.de>
 <CAApHDvpeXSU4A=mzX=96Rdn6u4gjVLHy8SMaVm_g01S8yhfAoQ@mail.gmail.com>
 <842393.1676218781@sss.pgh.pa.us>
 <CAApHDvrfuSuFq57EtbYxHNWYhMET9K_TpSefDUoM52-T6LCYbg@mail.gmail.com>
Comments: In-reply-to David Rowley <dgrowleyml@gmail.com>
	message dated "Mon, 13 Feb 2023 13:31:54 +1300"
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-ID: <988098.1676249737.1@sss.pgh.pa.us>
Date: Sun, 12 Feb 2023 19:55:37 -0500
Message-ID: <988099.1676249737@sss.pgh.pa.us>
Archived-At: 
 <https://www.postgresql.org/message-id/988099.1676249737%40sss.pgh.pa.us>
Precedence: bulk

David Rowley <dgrowleyml@gmail.com> writes:
> On Mon, 13 Feb 2023 at 05:19, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> Why is it okay to check only the filter, and not the rest of the
>> WindowFunc's subexpressions?  The arguments we've just run through
>> seem to apply to a subplan in the direct or aggregated arguments
>> as well.

> Good point.  I had just been thinking in terms of the reported bug to
> make sure we inverse transition the same rows we transition. We also
> need to make sure the transition value matches in both transition
> directions.
> I've adjusted the patch accordingly.

Code looks good now, but the comment still claims this is only
important in the FILTER clause.  I'd rewrite the whole thing
perhaps:

    * We also don't risk using moving aggregates when there are subplans
    * in the arguments or FILTER clause.  This is partly because
    * contain_volatile_functions() doesn't look inside subplans; but
    * there are other reasons why a subplan's output might be volatile.
    * For example, syncscan mode can render the results nonrepeatable.

			regards, tom lane