Message-ID: <1cd9d7e0-d1ae-4c74-91b5-fbbf8046ee56@data-bene.io>
Date: Tue, 8 Jul 2025 01:47:00 +0000
MIME-Version: 1.0
Subject: Re: Adding basic NUMA awareness - Preliminary feedback and outline
 for an extensible approach
To: Tomas Vondra <tomas@vondra.me>,
 PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
References: <099b9433-2855-4f1b-b421-d078a5d82017@vondra.me>
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> On 7/7/25 16:51, C=C3=A9dric Villemain wrote:
>>>> * Others might use it to integrate PostgreSQL's own resources (e.g.,
>>>> "areas" of shared buffers) into policies.
>>>>
>>>> Hope this perspective is helpful.
>>>
>>> Can you explain how you want to manage this by an extension defined a=
t
>>> the SQL level, when most of this stuff has to be done when setting up
>>> shared memory, which is waaaay before we have any access to catalogs?
>>
>> I should have said module instead, I didn't follow carefully but at so=
me
>> point there were discussion about shared buffers resized "on-line".
>> Anyway, it was just to give some few examples, maybe this one is to be
>> considered later (I'm focused on cgroup/psi, and precisely reassigning
>> PIDs as needed).
>>
>=20
> I don't know. I have a hard time imagining what exactly would the
> policies / profiles do exactly to respond to changes in the system
> utilization. And why should that interfere with this patch ...
>=20
> The main thing patch series aims to implement is partitioning different
> pieces of shared memory (buffers, freelists, ...) to better work for
> NUMA. I don't think there's that many ways to do this, and I doubt it
> makes sense to make this easily customizable from external modules of
> any kind. I can imagine providing some API allowing to isolate the
> instance on selected NUMA nodes, but that's about it.
>=20
> Yes, there's some relation to the online resizing of shared buffers, in
> which case we need to "refresh" some of the information. But AFAICS it'=
s
> not very extensive (on top of what already needs to happen after the
> resize), and it'd happen within the boundaries of the partitioning
> scheme. There's not that much flexibility.
>=20
> The last bit (pinning backends to a NUMA node) is experimental, and
> mostly intended for easier evaluation of the earlier parts (e.g. to
> limit the noise when processes get moved to a CPU from a different NUMA
> node, and so on).

The backend pinning can be done by replacing your patch on proc.c to=20
call an external profile manager doing exactly the same thing maybe ?

Similar to:
pmroutine =3D GetPmRoutineForInitProcess();
if (pmroutine !=3D NULL &&
	pmroutine->init_process !=3D NULL)
	pmroutine->init_process(MyProc);

...

pmroutine =3D GetPmRoutineForInitAuxilliary();
if (pmroutine !=3D NULL &&
	pmroutine->init_auxilliary !=3D NULL)
	pmroutine->init_auxilliary(MyProc);

Added on some rare places should cover most if not all the requirement=20
around process placement (process_shared_preload_libraries() is called=20
earlier in the process creation I believe).

--=20
C=C3=A9dric Villemain +33 6 20 30 22 52
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