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From: Andres Freund <andres@anarazel.de>
To: Laurenz Albe <laurenz.albe@cybertec.at>
Cc: Marc Rechté <marc4@rechte.fr>
Cc: pgsql-performance@lists.postgresql.org
Subject: Re: NUMA settings
Date: Mon, 4 May 2020 09:20:42 -0700
Message-ID: <20200504162042.3ctwpkg33trpyfdm@alap3.anarazel.de> (raw)
In-Reply-To: <e4d2e9c66efebc14e7f13ed2c26171f7cd9f85ac.camel@cybertec.at>
References: <2d10f8ab-5fc6-a0a5-facf-68f35de95ea9@rechte.fr>
	<e4d2e9c66efebc14e7f13ed2c26171f7cd9f85ac.camel@cybertec.at>

Hi,

On 2020-04-29 10:50:54 +0200, Laurenz Albe wrote:
> On Wed, 2020-04-29 at 08:54 +0200, Marc Rechté wrote:
> > I am trying to figure out the recommended settings for a PG dedicated 
> > machine regarding NUMA.
> > 
> > I assume that the shared buffers are using Huge Phages only. Please 
> > correct if I am wrong:
> > 
> > 1) postgres is started with numactl --interleave=all, in order to spread 
> > memory pages evenly on nodes.
> > 2) wm.swappiness is left to the default 60 value, because Huge Pages 
> > never swap, and we wish the idle backend to be swapped out if necessary.
> > 3) vm.zone_reclaim_mode = 0. I am not sure it is the right choice.
> > 4) kernel.numa_balancing = 1. Only if it is confirmed that it will not 
> > affect postgres, because started with the interleave policy.
> 
> I am not the top expert on this, but as far as I can tell:
> 
> - Disabling NUMA is good if you want to run a single database cluster
>   on the machine that should use all resources.
> 
>   If you want to run several clusters that share the resources, leaving
>   NUMA support enabled might be the better thing to do.
> 
> - If you can, disable NUMA in the BIOS, on as low a level as possible.

I am doubtful that that's generally going to be beneficial. I think the
strategy of starting postgres with interleave is probably a better
answer.

- Andres





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