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From: Koen De Groote <kdg.dev@gmail.com>
Date: Wed, 20 Nov 2024 12:06:07 +0100
Message-ID: <CAGbX52HN8FRkmN6zfAnevFRLw058B59mAEJbghLXeXcK_HZd+g@mail.gmail.com>
Subject: Re: Running docker in postgres, SHM size of the docker container in
 postgres 16
To: Thomas Munro <thomas.munro@gmail.com>
Cc: PostgreSQL General <pgsql-general@lists.postgresql.org>
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That explains a lot.

I have the default of 2 max_parallel_maintenance_workers set, should I set
this to 0?

I realize this is of course an improvement, but working with docker
containers, I'd like to avoid taking /dev/shm away from regular queries.

I assume setting max_parallel_maintenance_workers to 0 is the fix here, is
there perhaps something else I should know about, if I want to have control
over this?

Regards,
Koen De Groote


On Wed, Nov 20, 2024 at 12:38=E2=80=AFAM Thomas Munro <thomas.munro@gmail.c=
om>
wrote:

> On Wed, Nov 20, 2024 at 11:22=E2=80=AFAM Koen De Groote <kdg.dev@gmail.co=
m> wrote:
> > Why would that be? It's the exact same data. The install is about 50GB
> in size. Is there something wrong with postgres 16, or did some settings
> significantly change, that I need to know about? I went over all the
> changelogs, nothing stood out as relevant to this, but that might be a la=
ck
> of experience on my end.
>
> Parallel vacuum arrived in PostgreSQL 13, and that uses "dynamic
> shared memory" to share state between workers, and assuming
> dynamic_shared_memory_type=3Dposix, that means shm_open(), which opens
> files under /dev/shm on Linux.
>

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<div dir=3D"ltr">That explains a lot.<div><br></div><div>I have the default=
 of 2 max_parallel_maintenance_workers set, should I set this to 0?</div><d=
iv><br></div><div>I realize this is of course an improvement, but working w=
ith docker containers, I&#39;d like to avoid taking /dev/shm away from regu=
lar queries.</div><div><br></div><div>I assume setting max_parallel_mainten=
ance_workers to 0 is the fix here, is there perhaps something else I should=
 know about, if I want to have control over this?</div><div><br></div><div>=
Regards,</div><div>Koen De Groote</div><div><br></div><div><br></div></div>=
<br><div class=3D"gmail_quote"><div dir=3D"ltr" class=3D"gmail_attr">On Wed=
, Nov 20, 2024 at 12:38=E2=80=AFAM Thomas Munro &lt;<a href=3D"mailto:thoma=
s.munro@gmail.com">thomas.munro@gmail.com</a>&gt; wrote:<br></div><blockquo=
te class=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;border-left:1px =
solid rgb(204,204,204);padding-left:1ex">On Wed, Nov 20, 2024 at 11:22=E2=
=80=AFAM Koen De Groote &lt;<a href=3D"mailto:kdg.dev@gmail.com" target=3D"=
_blank">kdg.dev@gmail.com</a>&gt; wrote:<br>
&gt; Why would that be? It&#39;s the exact same data. The install is about =
50GB in size. Is there something wrong with postgres 16, or did some settin=
gs significantly change, that I need to know about? I went over all the cha=
ngelogs, nothing stood out as relevant to this, but that might be a lack of=
 experience on my end.<br>
<br>
Parallel vacuum arrived in PostgreSQL 13, and that uses &quot;dynamic<br>
shared memory&quot; to share state between workers, and assuming<br>
dynamic_shared_memory_type=3Dposix, that means shm_open(), which opens<br>
files under /dev/shm on Linux.<br>
</blockquote></div>

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