Horton

Re: Estimating HugePages Requirements?

Nathan Bossart <bossartn@amazon.com>

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From: "Bossart, Nathan" <bossartn@amazon.com>
To: Magnus Hagander <magnus@hagander.net>, Michael Paquier <michael@paquier.xyz>
Cc: Andres Freund <andres@anarazel.de>, Mark Dilger <mark.dilger@enterprisedb.com>, Don Seiler <don@seiler.us>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Date: 2021-08-27T18:16:01Z
Lists: pgsql-hackers

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On 8/27/21, 7:41 AM, "Magnus Hagander" <magnus@hagander.net> wrote:
> On Fri, Aug 27, 2021 at 8:46 AM Michael Paquier <michael@paquier.xyz> wrote:
>> On Wed, Aug 11, 2021 at 11:23:52PM +0000, Bossart, Nathan wrote:
>> > While testing this new option, I noticed that you can achieve similar
>> > results today with the following command, although this one will
>> > actually try to create the shared memory, too.
>>
>> That may not be the best option.
>
> I would say that can be a disastrous option.
>
> First of all it would probably not work if you already have something
> running -- especially when using huge pages. And if it does work, in
> that or other scenarios, it can potentially have significant impact on
> a running cluster to suddenly allocate many GB of more memory...

The v3 patch actually didn't work if the server was already running.
I removed that restriction in v4.

>> > IMO the new option is still handy, but I can see the argument that it
>> > might not be necessary.
>>
>> A separate option looks handy.  Wouldn't it be better to document it
>> in postgres-ref.sgml then?
>
> I'd say a lot more than just handy. I don't think the workaround is
> really all that useful.

I added some documentation in v4.

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.