Date: Fri, 17 Sep 2021 11:20:30 +0900
From: Michael Paquier <michael@paquier.xyz>
To: "Bossart, Nathan" <bossartn@amazon.com>
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>
Subject: Re: Estimating HugePages Requirements?
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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

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