Horton

Re: Estimating HugePages Requirements?

Nathan Bossart <bossartn@amazon.com>

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From: "Bossart, Nathan" <bossartn@amazon.com>
To: Michael Paquier <michael@paquier.xyz>
Cc: Justin Pryzby <pryzby@telsasoft.com>, Kyotaro Horiguchi <horikyota.ntt@gmail.com>, "tgl@sss.pgh.pa.us" <tgl@sss.pgh.pa.us>, "robertmhaas@gmail.com" <robertmhaas@gmail.com>, "masao.fujii@oss.nttdata.com" <masao.fujii@oss.nttdata.com>, "andres@anarazel.de" <andres@anarazel.de>, "magnus@hagander.net" <magnus@hagander.net>, "mark.dilger@enterprisedb.com" <mark.dilger@enterprisedb.com>, "don@seiler.us" <don@seiler.us>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Date: 2021-09-21T16:06:38Z
Lists: pgsql-hackers 
On 9/20/21, 7:29 PM, "Michael Paquier" <michael@paquier.xyz> wrote:
> On Tue, Sep 21, 2021 at 12:08:22AM +0000, Bossart, Nathan wrote:
>> Should we also initialize the shared memory GUCs in bootstrap and
>> single-user mode?  I think I missed this in bd17880.
>
> Why would we need that for the bootstrap mode?
>
> While looking at the patch for shared_memory_size, I have looked at
> those code paths to note that some of the runtime GUCs would be set
> thanks to the load of the control file, but supporting this case
> sounded rather limited to me for --single when it came to shared
> memory and huge page estimation and we don't load
> shared_preload_libraries in this context either, which could lead to
> wrong estimations.  Anyway, I am not going to fight hard if people
> would like that for the --single mode, even if it may lead to an
> underestimation of the shmem allocated.

I was looking at this from the standpoint of keeping the startup steps
consistent between the modes.  Looking again, I can't think of
a strong reason to add it to bootstrap mode.  I think the case for
adding it to single-user mode is a bit stronger, as commands like
"SHOW shared_memory_size;" currently return 0.  I lean in favor of
adding it for single-user mode, but it's probably fine either way.

Nathan

Commits

  1. Silence extra logging when using "postgres -C" on runtime-computed GUCs

  2. doc: Improve postgres command for shared_memory_size_in_huge_pages

  3. Introduce GUC shared_memory_size_in_huge_pages

  4. Support "postgres -C" with runtime-computed GUCs

  5. Make shared_memory_size a preset option

  6. Introduce GUC shared_memory_size

  7. Move the shared memory size calculation to its own function

  8. Add new GUC, max_worker_processes, limiting number of bgworkers.