Re: NUMA settings

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