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From: Marc Millas <marc.millas@mokadb.com>
Date: Fri, 25 Apr 2025 18:13:14 +0200
Message-ID: <CADX_1aZsMWO7S+fGs8-vTYke1244U1n8T9eT4vPYexKPmSPX+Q@mail.gmail.com>
Subject: Re: shared buffers
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Sorry,

'someone' launches some kind of batches without telling.

Marc MILLAS
Senior Architect
+33607850334
www.mokadb.com


On Fri, Apr 25, 2025 at 3:42=E2=80=AFPM Marc Millas <marc.millas@mokadb.com=
> wrote:

> hello,
>
> got something strange to me:
> Same db ie. same data, around 1.2TB,one on pg13, one on pg16
> same 16 GB of shared_buffers,
> I am the single user.
> both have track_io_timing on
>
> on pg13, if I run a big request with explain (analyze,buffers),
> I see around 6 GB read
> if I do rerun the very same request, no more read(s), all data in the
> shared buffers cache. fine
> If I check with pg_buffercache what's in it, I see the biggest tables of
> my request within the biggest users (in number of blocks used). All this =
is
> fine.
>
> next, if I do the very same on the pg16 machine, whatever the number of
> times I rerun the explain (analyze, buffers) of the same request, each
> time, the explain shows the same volume of reads. again and again.
> If I check with pg_buffercache, the set of objects stay the same, WITHOUT
> the objects of my request, just like if those objects where sticky.
>
> any idea ?
>
> thanks
>
> Marc MILLAS
> Senior Architect
> +33607850334
> www.mokadb.com
>
>

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<div dir=3D"ltr"><div>Sorry,</div><div><br></div><div>&#39;someone&#39; lau=
nches some kind of batches without telling.</div><div><br></div><div><div d=
ir=3D"ltr" class=3D"gmail_signature" data-smartmail=3D"gmail_signature"><di=
v dir=3D"ltr"><div><div dir=3D"ltr">Marc MILLAS<div>Senior Architect</div><=
div>+33607850334</div><div><a href=3D"http://www.mokadb.com" target=3D"_bla=
nk">www.mokadb.com</a></div><div><br></div></div></div></div></div></div><b=
r></div><br><div class=3D"gmail_quote gmail_quote_container"><div dir=3D"lt=
r" class=3D"gmail_attr">On Fri, Apr 25, 2025 at 3:42=E2=80=AFPM Marc Millas=
 &lt;<a href=3D"mailto:marc.millas@mokadb.com">marc.millas@mokadb.com</a>&g=
t; wrote:<br></div><blockquote class=3D"gmail_quote" style=3D"margin:0px 0p=
x 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div d=
ir=3D"ltr"><div>hello,</div><div><br></div><div>got something strange to me=
:</div><div>Same db ie. same data, around 1.2TB,one on pg13, one on pg16</d=
iv><div>same 16 GB of shared_buffers,</div><div>I am the single user.</div>=
<div>both have track_io_timing on</div><div><br></div><div>on pg13, if I ru=
n a big request with explain (analyze,buffers),=C2=A0</div><div>I see aroun=
d 6 GB read</div><div>if I do rerun the very same request, no more read(s),=
 all data in the shared buffers cache. fine</div><div>If I check with pg_bu=
ffercache what&#39;s in it, I see the biggest tables of my request within t=
he biggest users (in number of blocks used). All this is fine.</div><div><b=
r></div><div>next, if I do the very same on the pg16 machine, whatever the =
number of times I rerun the explain=C2=A0(analyze, buffers) of the same req=
uest, each time, the explain shows the same volume of reads. again and agai=
n.</div><div>If I check with pg_buffercache, the set of objects stay the sa=
me, WITHOUT the objects of my request, just like if those objects where sti=
cky.</div><div><br></div><div>any idea ?</div><div><br></div><div>thanks</d=
iv><div><br></div><div><div dir=3D"ltr" class=3D"gmail_signature"><div dir=
=3D"ltr"><div><div dir=3D"ltr">Marc MILLAS<div>Senior Architect</div><div>+=
33607850334</div><div><a href=3D"http://www.mokadb.com" target=3D"_blank">w=
ww.mokadb.com</a></div><div><br></div></div></div></div></div></div></div>
</blockquote></div>

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