From: Andres Freund <andres@anarazel.de>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Andrew Gierth <andrew@tao11.riddles.org.uk>
Cc: 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.)
Date: Thu, 6 Jun 2019 10:18:50 -0700
Message-ID: <20190606171850.ilssehzrvrrfuiqs@alap3.anarazel.de> (raw)
In-Reply-To: <5519.1559839890@sss.pgh.pa.us>
References: <E1hK8qL-0005yH-VX@gemulon.postgresql.org>
<20190604085735.GD24018@msg.df7cb.de>
<87ftop8gtr.fsf@news-spur.riddles.org.uk>
<20190604164457.772invck3lgxk75s@alap3.anarazel.de>
<5519.1559839890@sss.pgh.pa.us>
Hi,
On 2019-06-06 12:51:30 -0400, Tom Lane wrote:
> [ sorry for slow response, I'm on vacation ]
Good.
> Andres Freund <andres@anarazel.de> writes:
> > That makes sense. As far as I can tell the reason that 12 sometimes ends
> > up with the proper timezone is that we shortcut the search by:
>
> > /*
> > * Try to avoid the brute-force search by seeing if we can recognize the
> > * system's timezone setting directly.
> > *
> > * Currently we just check /etc/localtime; there are other conventions for
> > * this, but that seems to be the only one used on enough platforms to be
> > * worth troubling over.
> > */
> > if (check_system_link_file("/etc/localtime", &tt, resultbuf))
> > return resultbuf;
>
> > which is actually a behaviour changing, rather than just an
> > optimization, when there's a lot of equivalently scoring timezones.
>
> Sure, that is intentionally a behavior change in this situation.
> The theory is that if "Etc/UCT" is what the user put in /etc/localtime,
> then that's the spelling she wants. See 23bd3cec6.
Right, I'm not complaining about that. I'm just noting that that
explains the cross-version divergence.
Note that on 11 I *do* end up with some *other* timezone with the newer
timezone data:
$cat /etc/timezone;ls -l /etc/localtime
Etc/UTC
lrwxrwxrwx 1 root root 27 Jun 6 17:02 /etc/localtime -> /usr/share/zoneinfo/Etc/UTC
$ rm -rf /tmp/tztest;~/build/postgres/11-assert/install/bin/initdb /tmp/tztest 2>&1|grep -v 'scores 0'|grep -v 'uses leap seconds';grep timezone /tmp/tztest/postgresql.conf
...
TZ "Zulu" gets max score 5200
TZ "UCT" gets max score 5200
TZ "Universal" gets max score 5200
TZ "UTC" gets max score 5200
TZ "Etc/Zulu" gets max score 5200
TZ "Etc/UCT" gets max score 5200
TZ "Etc/Universal" gets max score 5200
TZ "Etc/UTC" gets max score 5200
TZ "localtime" gets max score 5200
TZ "posix/Zulu" gets max score 5200
TZ "posix/UCT" gets max score 5200
TZ "posix/Universal" gets max score 5200
TZ "posix/UTC" gets max score 5200
TZ "posix/Etc/Zulu" gets max score 5200
TZ "posix/Etc/UCT" gets max score 5200
TZ "posix/Etc/Universal" gets max score 5200
TZ "posix/Etc/UTC" gets max score 5200
ok
...
log_timezone = 'UCT'
timezone = 'UCT'
#timezone_abbreviations = 'Default' # Select the set of available time zone
# share/timezonesets/.
As you can see the switch from Etc/UTC to UCT does happen here
(presumably in any branch before 12). Which did not happen before the
import of 2019a / when using a system tzdata that's before
that. There you get:
TZ "Zulu" gets max score 5200
TZ "Universal" gets max score 5200
TZ "UTC" gets max score 5200
TZ "Etc/Zulu" gets max score 5200
TZ "Etc/Universal" gets max score 5200
TZ "Etc/UTC" gets max score 5200
ok
and end up with UTC as the selection.
I do think that < 12 clearly regressed here, although it's only exposing
previous behaviour further.
Greetings,
Andres Freund
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Cc: andres@anarazel.de, tgl@sss.pgh.pa.us, andrew@tao11.riddles.org.uk, myon@debian.org, pgsql-hackers@postgresql.org
Subject: Re: UCT (Re: pgsql: Update time zone data files to tzdata release 2019a.)
In-Reply-To: <20190606171850.ilssehzrvrrfuiqs@alap3.anarazel.de>
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