Re: BitmapHeapScan streaming read user and prelim refactoring

From: Melanie Plageman <melanieplageman(at)gmail(dot)com>
To: Michael Paquier <michael(at)paquier(dot)xyz>
Cc: Tomas Vondra <tomas(dot)vondra(at)enterprisedb(dot)com>, Thomas Munro <thomas(dot)munro(at)gmail(dot)com>, Heikki Linnakangas <hlinnaka(at)iki(dot)fi>, Andres Freund <andres(at)anarazel(dot)de>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org>, Nazir Bilal Yavuz <byavuz81(at)gmail(dot)com>
Subject: Re: BitmapHeapScan streaming read user and prelim refactoring
Date: 2024-05-14 17:42:09
Message-ID: CAAKRu_ZwjB7b+_FS3h1_bdr4wY9xGcy47iE3o7kdHzOh3ALPfA@mail.gmail.com
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On Tue, May 14, 2024 at 2:18 AM Michael Paquier <michael(at)paquier(dot)xyz> wrote:
>
> On Mon, May 13, 2024 at 10:05:03AM -0400, Melanie Plageman wrote:
> > Remove the assert and reset the field on which it previously asserted to
> > avoid incorrectly emitting NULL-filled tuples from a previous scan on
> > rescan.
>
> > - Assert(scan->rs_empty_tuples_pending == 0);
> > + scan->rs_empty_tuples_pending = 0;
>
> Perhaps this should document the reason why the reset is done in these
> two paths rather than let the reader guess it? And this is about
> avoiding emitting some tuples from a previous scan.

I've added a comment to heap_rescan() in the attached v5. Doing so
made me realize that we shouldn't bother resetting it in
heap_endscan(). Doing so is perhaps more confusing, because it implies
that field may somehow be used later. I've removed the reset of
rs_empty_tuples_pending from heap_endscan().

> > +SET enable_indexonlyscan = off;
> > +set enable_indexscan = off;
> > +SET enable_seqscan = off;
>
> Nit: adjusting the casing of the second SET here.

I've fixed this. I've also set enable_material off as I mentioned I
might in my earlier mail.

- Melanie

Attachment Content-Type Size
v5-0001-BitmapHeapScan-Remove-incorrect-assert-and-reset-.patch text/x-patch 5.6 KB

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