From: Tom Lane <tgl@sss.pgh.pa.us>
To: Andrew Dunstan <andrew@dunslane.net>
cc: Thomas Munro <thomas.munro@gmail.com>,
        Jakub Wartak <jakub.wartak@enterprisedb.com>,
        Bruce Momjian <bruce@momjian.us>, Dimitrios Apostolou <jimis@gmx.net>,
        Magnus Hagander <magnus@hagander.net>, Tomas Vondra <tomas@vondra.me>,
        pgsql-hackers@lists.postgresql.org, Andres Freund <andres@anarazel.de>,
        Melanie Plageman <melanieplageman@gmail.com>,
        Heikki Linnakangas <hlinnaka@iki.fi>,
        Kyotaro Horiguchi <horikyota.ntt@gmail.com>,
        David Rowley <dgrowleyml@gmail.com>
Subject: Re: [PING] fallocate() causes btrfs to never compress postgresql files
In-reply-to: <e1f0cd3b-0164-45f5-9705-e922e59df90f@dunslane.net>
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Comments: In-reply-to Andrew Dunstan <andrew@dunslane.net>
	message dated "Fri, 06 Feb 2026 10:33:55 -0500"
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Date: Fri, 06 Feb 2026 13:31:02 -0500
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Andrew Dunstan <andrew@dunslane.net> writes:
> On 2026-02-06 Fr 10:11 AM, Tom Lane wrote:
>> The message is complaining that sizeof(ConfigureNamesEnum) changed,
>> which it did, but I don't see how that value would be visible to
>> external modules.  So maybe a bug in libabigail?

> I guess because of this in guc_tables.h:
> extern PGDLLIMPORT struct config_generic ConfigureNames[];

Evidently, but I don't see how that provides a sizeof() value to
onlookers.  Just to be sure, I tried to compile a use of that,
and got

test.c:43:53: error: invalid application of =E2=80=98sizeof=E2=80=99 to in=
complete type =E2=80=98struct config_generic[]=E2=80=99
  elog(NOTICE, "sizeof(ConfigureNames) =3D %zu", sizeof(ConfigureNames));
                                                     ^

So if this isn't an outright bug, it's at least unhelpful behavior.

			regards, tom lane