From: Tom Lane <tgl@sss.pgh.pa.us>
To: Christoph Berg <myon@debian.org>
cc: PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Subject: Re: UCT (Re: pgsql: Update time zone data files to tzdata release
 2019a.)
In-reply-to: <20190604085735.GD24018@msg.df7cb.de>
References: <E1hK8qL-0005yH-VX@gemulon.postgresql.org>
 <20190604085735.GD24018@msg.df7cb.de>
Comments: In-reply-to Christoph Berg <myon@debian.org>
	message dated "Tue, 04 Jun 2019 10:57:35 +0200"
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Date: Tue, 04 Jun 2019 11:27:31 -0400
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Christoph Berg <myon@debian.org> writes:
> There is something wrong here. On Debian Buster/unstable, using
> system tzdata (2019a-1), if /etc/timezone is "Etc/UTC":

> 11.3's initdb adds timezone = 'UCT' to postgresql.conf
> 12beta1's initdb add timezone = 'Etc/UCT' to postgresql.conf

Hm, I don't have a Debian machine at hand, but I'm unable to
reproduce this using macOS or RHEL.  I tried things like

$ TZ=UTC initdb
...
selecting default timezone ... UTC
...

Is your build using --with-system-tzdata?  If so, which tzdb
release is the system on, and is it a completely stock copy
of that release?

Given the tie-breaking behavior in findtimezone.c,

 * ... Often there will be several
 * zones with identical rankings (since the IANA database assigns multiple
 * names to many zones).  We break ties arbitrarily by preferring shorter,
 * then alphabetically earlier zone names.

it's not so surprising that UCT might be chosen, but I don't
understand how Etc/UCT would be.

BTW, does Debian set up /etc/timezone as a symlink, by any chance,
rather than a copy or hard link?  If it's a symlink, we could improve
matters by teaching identify_system_timezone() to inspect it.

			regards, tom lane