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From: Magnus Hagander <magnus@hagander.net>
Date: Mon, 25 Apr 2022 16:55:25 +0200
Message-ID: 
 <CABUevEyD_aLM=oXi1jj8hRN=7aJq--jN4FP+ehY8Vu60+QH61A@mail.gmail.com>
Subject: Re: Estimating HugePages Requirements?
To: Michael Paquier <michael@paquier.xyz>
Cc: Nathan Bossart <nathandbossart@gmail.com>, "Bossart,
 Nathan" <bossartn@amazon.com>,
	Fujii Masao <masao.fujii@oss.nttdata.com>,
 Justin Pryzby <pryzby@telsasoft.com>,
	Andres Freund <andres@anarazel.de>,
 Mark Dilger <mark.dilger@enterprisedb.com>,
	Don Seiler <don@seiler.us>,
 PostgreSQL-development <pgsql-hackers@postgresql.org>
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On Mon, Apr 25, 2022 at 2:15 AM Michael Paquier <michael@paquier.xyz> wrote:

> On Fri, Apr 22, 2022 at 09:49:34AM +0200, Magnus Hagander wrote:
> > I agree that thats a very narrow use case. And I'm not sure the use case
> of
> > a running server is even that important here - it's really the offline
> one
> > that's important. Or rather, the really compelling one is when there is a
> > server running but I want to check the value offline because it will
> > change. SHOW doesn't help there because it shows the value based on the
> > currently running configuration, not the new one after a restart.
>
> You mean the case of a server where one would directly change
> postgresql.conf on a running server, and use postgres -C to see how
> much the kernel settings need to be changed before the restart?
>

Yes.

AIUI that was the original use-case for this feature. It certainly was for
me :)


> Hmm. So what's the solution on windows? I guess maybe it's not as
> important
> > there because there is no limit on huge pages, but generally getting the
> > expected shared memory usage might be useful? Just significantly less
> > important.
>
> Contrary to Linux, we don't need to care about the number of large
> pages that are necessary because there is no equivalent of
> vm.nr_hugepages on Windows (see [1]), do we?  If that were the case,
> we'd have a use case for huge_page_size, additionally.
>

Right, for this one in particular -- that's what I meant with my comment
about there not being a limit. But this feature works for other settings as
well, not just the huge pages one.  Exactly what the use-cases are can
vary, but surely they would have the same problems wrt redirects?


-- 
 Magnus Hagander
 Me: https://www.hagander.net/ <http://www.hagander.net/>
 Work: https://www.redpill-linpro.com/ <http://www.redpill-linpro.com/>

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<div dir=3D"ltr"><div dir=3D"ltr">On Mon, Apr 25, 2022 at 2:15 AM Michael P=
aquier &lt;<a href=3D"mailto:michael@paquier.xyz">michael@paquier.xyz</a>&g=
t; wrote:<br></div><div class=3D"gmail_quote"><blockquote class=3D"gmail_qu=
ote" style=3D"margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,20=
4);padding-left:1ex">On Fri, Apr 22, 2022 at 09:49:34AM +0200, Magnus Hagan=
der wrote:<br>
&gt; I agree that thats a very narrow use case. And I&#39;m not sure the us=
e case of<br>
&gt; a running server is even that important here - it&#39;s really the off=
line one<br>
&gt; that&#39;s important. Or rather, the really compelling one is when the=
re is a<br>
&gt; server running but I want to check the value offline because it will<b=
r>
&gt; change. SHOW doesn&#39;t help there because it shows the value based o=
n the<br>
&gt; currently running configuration, not the new one after a restart.<br>
<br>
You mean the case of a server where one would directly change<br>
postgresql.conf on a running server, and use postgres -C to see how<br>
much the kernel settings need to be changed before the restart?<br></blockq=
uote><div><br></div><div>Yes.</div><div><br></div><div>AIUI that was the or=
iginal use-case for this feature. It certainly was for me :)</div><div><br>=
</div><div><br></div><div><br></div><blockquote class=3D"gmail_quote" style=
=3D"margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding=
-left:1ex">
&gt; Hmm. So what&#39;s the solution on windows? I guess maybe it&#39;s not=
 as important<br>
&gt; there because there is no limit on huge pages, but generally getting t=
he<br>
&gt; expected shared memory usage might be useful? Just significantly less<=
br>
&gt; important.<br>
<br>
Contrary to Linux, we don&#39;t need to care about the number of large<br>
pages that are necessary because there is no equivalent of<br>
vm.nr_hugepages on Windows (see [1]), do we?=C2=A0 If that were the case,<b=
r>
we&#39;d have a use case for huge_page_size, additionally.<br></blockquote>=
<div><br></div><div>Right, for this one in particular -- that&#39;s what I =
meant with my comment about there not being a limit. But this feature works=
 for other settings as well, not just the huge pages one.=C2=A0 Exactly wha=
t the use-cases are can vary, but surely they would have the same problems =
wrt redirects?</div><div><br></div><div><br></div></div>-- <br><div dir=3D"=
ltr" class=3D"gmail_signature"><div dir=3D"ltr"><div>=C2=A0Magnus Hagander<=
br>=C2=A0Me: <a href=3D"http://www.hagander.net/" target=3D"_blank">https:/=
/www.hagander.net/</a><br>=C2=A0Work: <a href=3D"http://www.redpill-linpro.=
com/" target=3D"_blank">https://www.redpill-linpro.com/</a></div></div></di=
v></div>

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