Date: Wed, 5 Sep 2018 12:35:25 +0200
From: Christoph Berg <myon@debian.org>
To: Thomas Munro <thomas.munro@enterprisedb.com>
Cc: Pg Hackers <pgsql-hackers@postgresql.org>
Subject: Re: Collation versioning
Message-ID: <20180905103524.GA13620@msg.df7cb.de>
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	Thomas Munro <thomas.munro@enterprisedb.com>,
	Pg Hackers <pgsql-hackers@postgresql.org>
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Re: Thomas Munro 2018-09-04 <CAEepm=0uEQCpfq_+LYFBdArCe4Ot98t1aR4eYiYTe=yavQygiQ@mail.gmail.com>
> I was reminded about that by recent news
> about an upcoming glibc/CLDR resync that is likely to affect
> PostgreSQL users (though, I guess, probably only when they do a major
> OS upgrade).

Or replicating/restoring a database to a newer host.

> ... or, on a Debian system using the locales package, like this:
> 
> libc_collation_version_command = 'dpkg -s locales | grep Version: |
> sed "s/Version: //"'

Ugh. This sounds horribly easy to get wrong on the user side. I could
of course put that preconfigured into the Debian packages, but that
would leave everyone not using any of the standard distro packagings
in the rain.

> Does anyone know
> of a way to extract a version string from glibc using existing
> interfaces?  I heard there was an undocumented way but I haven't been
> able to find it -- probably because I was, erm, looking in the
> documentation.

That sounds more robust. Googling around:

https://www.linuxquestions.org/questions/linux-software-2/how-to-check-glibc-version-263103/

#include <stdio.h>
#include <gnu/libc-version.h>
int main (void) { puts (gnu_get_libc_version ()); return 0; }

$ ./a.out
2.27

Hopefully that version info is fine-grained enough.

Christoph