Re: Estimating HugePages Requirements?

On Mon, Apr 25, 2022 at 04:55:25PM +0200, Magnus Hagander wrote:
> AIUI that was the original use-case for this feature. It certainly was for
> me :)

Perhaps we'd be fine with relaxing the requirements here knowing that
the control file should never be larger than PG_CONTROL_MAX_SAFE_SIZE
(aka the read should be atomic so it could be made lockless). At the
end of the day, to be absolutely correct in the shmem size estimation,
I think that we are going to need what's proposed here or the sizing
may not be right depending on how extensions adjust GUCs after they
load their _PG_init():
https://www.postgresql.org/message-id/20220419154658.GA2487941@nathanxps13

That's a bit independent, but not completely unrelated either
depending on how exact you want your number of estimated huge pages to
be. Just wanted to mention it.

>> Contrary to Linux, we don't need to care about the number of large
>> pages that are necessary because there is no equivalent of
>> vm.nr_hugepages on Windows (see [1]), do we? If that were the case,
>> we'd have a use case for huge_page_size, additionally.
>
> Right, for this one in particular -- that's what I meant with my comment
> about there not being a limit. But this feature works for other settings as
> well, not just the huge pages one. Exactly what the use-cases are can
> vary, but surely they would have the same problems wrt redirects?

Yes, the redirection issue would apply to all the run-time GUCs.
--
Michael