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In-Reply-To: <9411f220-007d-4f1e-9c8f-ca8eb09e6788@vondra.me>
From: Alexandre Felipe <o.alexandre.felipe@gmail.com>
Date: Sun, 15 Feb 2026 08:08:34 +0000
Message-ID: <CAE8JnxNvssQBKJPmVhkeQBk_mEi3deR_ij10+7MAN+6y9WFDrQ@mail.gmail.com>
Subject: Re: index prefetching
To: Tomas Vondra <tomas@vondra.me>
Cc: Peter Geoghegan <pg@bowt.ie>, Andres Freund <andres@anarazel.de>, 
	Thomas Munro <thomas.munro@gmail.com>, Nazir Bilal Yavuz <byavuz81@gmail.com>, 
	Robert Haas <robertmhaas@gmail.com>, Melanie Plageman <melanieplageman@gmail.com>, 
	PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Georgios <gkokolatos@protonmail.com>, 
	Konstantin Knizhnik <knizhnik@garret.ru>, Dilip Kumar <dilipbalaut@gmail.com>
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Another quick response, I am impressed

I'm quite confused by the scripts you shared, it seems incomplete. The
> run_regression.py is meant to call purge_cache.sh (which is missing),
> and the run_benchmark tries to call all sorts of missing .sql scripts.
>

That was a confusion I did, I uploaded run_benchmark that was just a
nonsensical AI generated script in my work area and I didn't upload
purge_cache.sh. Notice that you can still run the python script with evict
mode off,pg. The missing script is attached in my previous message.


> A table that is just 24MB and fits into buffers is a bit useless. It
> means that even with random pattern (which is generally about the best
> for prefetching), only about ~1/30 of pages will require I/O. Each page
> has ~32 items, but only the first item from each page will incur an I/O.
>

OK, I will start it with different parameters, for development I needed
something that was not too slow, to be able to catch the bugs.

On what kind of hardware? How much variance is in the results?
>
Is a Mac mini M1. Please check the .PNG it shows the confidence intervals
of the difference of execution time with the parameter ON and OFF, with
different settings.

--
Alexandre

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<div dir=3D"ltr"><div dir=3D"ltr">Another quick response, I am impressed</d=
iv><div dir=3D"ltr"><br></div><div class=3D"gmail_quote gmail_quote_contain=
er"><blockquote class=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;bor=
der-left:1px solid rgb(204,204,204);padding-left:1ex">
I&#39;m quite confused by the scripts you shared, it seems incomplete. The<=
br>
run_regression.py is meant to call purge_cache.sh (which is missing),<br>
and the run_benchmark tries to call all sorts of missing .sql scripts.<br><=
/blockquote><div><br></div><div>That was a confusion I did, I uploaded run_=
benchmark that was just a nonsensical AI generated script in my work area a=
nd I didn&#39;t upload purge_cache.sh. Notice that you can still run the py=
thon script with evict mode off,pg. The missing script is attached in my pr=
evious message.=C2=A0</div><div>=C2=A0</div><blockquote class=3D"gmail_quot=
e" style=3D"margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204)=
;padding-left:1ex">
A table that is just 24MB and fits into buffers is a bit useless. It<br>
means that even with random pattern (which is generally about the best<br>
for prefetching), only about ~1/30 of pages will require I/O. Each page<br>
has ~32 items, but only the first item from each page will incur an I/O.=C2=
=A0<br></blockquote><div><br></div><div>OK, I will start it with different =
parameters, for development I needed something that was not too slow, to be=
 able to catch=C2=A0the bugs.</div><div><br></div><blockquote class=3D"gmai=
l_quote" style=3D"margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,20=
4,204);padding-left:1ex">
On what kind of hardware? How much variance is in the results?<br></blockqu=
ote><div>Is a Mac mini M1. Please check the .PNG it shows the confidence in=
tervals of the difference of execution time with the parameter ON and OFF, =
with different settings.</div><div><br></div><div>--</div><div>Alexandre</d=
iv></div></div>

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