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From: Matthias van de Meent <boekewurm+postgres@gmail.com>
Date: Fri, 28 Jul 2023 13:11:47 +0200
Message-ID: <CAEze2Wh+FK5Z3EYLoXQkCjV1YqNhbz-sMJv_gxbnnCsEs7c3Ww@mail.gmail.com>
Subject: Re: Optimizing nbtree ScalarArrayOp execution, allowing multi-column
 ordered scans, skip scan
To: Peter Geoghegan <pg@bowt.ie>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Tom Lane <tgl@sss.pgh.pa.us>, 
	Tomas Vondra <tomas.vondra@enterprisedb.com>, Jeff Davis <pgsql@j-davis.com>, 
	benoit <benoit@hopsandfork.com>
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On Thu, 27 Jul 2023 at 16:01, Peter Geoghegan <pg@bowt.ie> wrote:
>
> On Thu, Jul 27, 2023 at 7:59=E2=80=AFAM Matthias van de Meent
> <boekewurm+postgres@gmail.com> wrote:
> > > Basically, the patch that added that feature had to revise the index
> > > AM API, in order to support a mode of operation where scans return
> > > groupings rather than tuples. Whereas this patch requires none of
> > > that. It makes affected index scans as similar as possible to
> > > conventional index scans.
> >
> > Hmm, yes. I see now where my confusion started. You called it out in
> > your first paragraph of the original mail, too, but that didn't help
> > me then:
> >
> > The wiki does not distinguish "Index Skip Scans" and "Loose Index
> > Scans", but these are not the same.
>
> A lot of people (myself included) were confused on this point for
> quite a while.

I've taken the liberty to update the "Loose indexscan" wiki page [0],
adding detail that Loose indexscans are distinct from Skip scans, and
showing some high-level distinguishing properties.
I also split the TODO entry for `` "loose" or "skip" scan `` into two,
and added links to the relevant recent threads so that it's clear
these are different (and that some previous efforts may have had a
confusing name).

I hope this will reduce the chance of future confusion between the two
different approaches to improving index scan performance.

Kind regards,

Matthias van de Meent
Neon (https://neon.tech)

[0]: https://wiki.postgresql.org/wiki/Loose_indexscan