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help / color / mirror / Atom feedFrom: Peter Geoghegan <[email protected]>
To: Andres Freund <[email protected]>
Cc: Tom Lane <[email protected]>
Cc: Matthias van de Meent <[email protected]>
Cc: Konstantin Knizhnik <[email protected]>
Cc: PostgreSQL Hackers <[email protected]>
Subject: Re: Incorrect result of bitmap heap scan.
Date: Mon, 2 Dec 2024 16:16:19 -0500
Message-ID: <CAH2-Wzmit-OxVZ4aaqAuOpX2NqSX4iayV_37bpdKRZybwOHPcg@mail.gmail.com> (raw)
In-Reply-To: <6nev7zfx57h5pkqpgdp4q37xjcj2dxqilsgbb5ac5lhub4whsb@ap7ptu6yqyj6>
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On Mon, Dec 2, 2024 at 3:55 PM Andres Freund <[email protected]> wrote:
> I suspect one contributor to this avoiding attention till now was that the
> optimization is fairly narrow:
>
> /*
> * We can potentially skip fetching heap pages if we do not need
> * any columns of the table, either for checking non-indexable
> * quals or for returning data. This test is a bit simplistic, as
> * it checks the stronger condition that there's no qual or return
> * tlist at all. But in most cases it's probably not worth working
> * harder than that.
> */
> need_tuples = (node->ss.ps.plan->qual != NIL ||
> node->ss.ps.plan->targetlist != NIL);
>
> Even an entry in the targetlist that that does not depend on the current row
> disables the optimization.
Good point. I agree that that factor is likely to have masked the
problem over the past 6 years.
--
Peter Geoghegan
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Subject: Re: Incorrect result of bitmap heap scan.
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