Feedback-ID: i0fe9450f:Fastmail
Date: Mon, 20 Mar 2023 13:54:46 +0900
From: Michael Paquier <michael@paquier.xyz>
To: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Cc: sfrost@snowman.net, pryzby@telsasoft.com, alvherre@alvh.no-ip.org,
	andres@anarazel.de, nathandbossart@gmail.com,
	jchampion@timescale.com, john.naylor@enterprisedb.com,
	masao.fujii@oss.nttdata.com, noriyoshi.shinoda@hpe.com,
	pgsql-hackers@postgresql.org, rjuju123@gmail.com,
	sawada.mshk@gmail.com, tgl@sss.pgh.pa.us, thomas.munro@gmail.com
Subject: Re: Improve logging when using Huge Pages
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On Tue, Mar 14, 2023 at 02:02:19PM +0900, Kyotaro Horiguchi wrote:
> Regarding huge_page_active, its value remains constant throughout a
> postmaster's lifespan. In this regard, GUC may be a better fit for
> this information.  The issue with using GUC for this value is that the
> postgres command cannot report the final value via the -C option,
> which may be the reason for the third alternative "unknown".
>=20
> I slightly prefer using a function for this, as if GUC is used, it can
> only return "unknown" for the command "postgres -C
> huge_page_active". However, apart from this advantage, I prefer using
> a GUC for this information.

The main advantage of a read-only GUC over a function is that users
would not need to start a postmaster to know if huge pages would be
active or not.  This is the main reason why a GUC would be a better
fit, in my opinion, because it makes for a cheaper check, while still
allowing a SQL query to check the value of the GUC.
--
Michael

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