Re: Estimating HugePages Requirements?

On Thu, Sep 16, 2021 at 09:26:56PM +0000, Bossart, Nathan wrote:
> I'm not sure I agree on this one. The documentation for huge_pages
> [0] and shared_memory_type [1] uses the same phrasing multiple times,
> and the new shared_memory_size GUC uses it as well [2]. I don't see
> anything in the documentation that suggests that shared_buffers is the
> only thing in the main shared memory area, and the documentation for
> setting up huge pages makes no mention of any extra memory that needs
> to be considered, either.

Looks rather sane to me, FWIW. I have not tested on Linux properly
yet (not tempted to take my bets on the buildfarm on a Friday,
either), but I should be able to handle that at the beginning of next
week.

+ GetHugePageSize(&hp_size, &unused);
+ if (hp_size != 0)
I'd rather change GetHugePageSize() to be able to accept NULL for the
parameter values, rather than declaring such variables.

+ To determine the number of huge pages needed, use the
+ <command>postgres</command> command to see the value of
+ <xref linkend="guc-shared-memory-size-in-huge-pages"/>.
We may want to say as well here that the server should be offline?
It would not hurt to duplicate this information with
postgres-ref.sgml.

+ This setting is supported only on Linux. It is always set to
Nit: This paragraph is missing two <productname>s for Linux. The docs
are random about that, but these are new entries.
--
Michael