Horton

Re: UCT (Re: pgsql: Update time zone data files to tzdata release 2019a.)

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Andres Freund <andres@anarazel.de>
Cc: Andrew Gierth <andrew@tao11.riddles.org.uk>, Christoph Berg <myon@debian.org>, PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Date: 2019-06-06T16:51:30Z
Lists: pgsql-hackers 
[ sorry for slow response, I'm on vacation ]

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.

But it seems to me that this code is *not* determining the result in
Christoph's case, because if it were, it'd be settling on Etc/UTC,
according to his followup report that

>> lrwxrwxrwx 1 root root 27 Mär 28 14:49 /etc/localtime -> /usr/share/zoneinfo/Etc/UTC

I'm not too familiar with what actually determines glibc's behavior
on Debian, but I'm suspicious that there's an inconsistency between
/etc/localtime and /etc/timezone.  We won't adopt the spelling we
see in /etc/localtime unless it agrees with the observed behavior of
localtime(3).

			regards, tom lane

Commits

  1. Tweak our special-case logic for the IANA "Factory" timezone.

  2. Avoid choosing "localtime" or "posixrules" as TimeZone during initdb.

  3. Prefer timezone name "UTC" over alternative spellings.

  4. Attempt to identify system timezone by reading /etc/localtime symlink.

  5. Update time zone data files to tzdata release 2019a.