Date: Thu, 1 Aug 2019 11:25:23 -0700
From: Andres Freund <andres@anarazel.de>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Shay Rojansky <roji@roji.org>, Thomas Munro <thomas.munro@gmail.com>,
	Andrew Gierth <andrew@tao11.riddles.org.uk>,
	Robert Haas <robertmhaas@gmail.com>,
	Stephen Frost <sfrost@snowman.net>,
	Christoph Berg <myon@debian.org>,
	PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Subject: Re: UCT (Re: pgsql: Update time zone data files to tzdata release
 2019a.)
Message-ID: <20190801182523.z6onphd2tqkjf2ch@alap3.anarazel.de>
References: 
 <CA+hUKGLZN3XHqZPN08itV4W-Nu3ndZ9zKJGSvzoWLm6AU9vz-g@mail.gmail.com>
 <8736jwsdv2.fsf@news-spur.riddles.org.uk>
 <17148.1561568815@sss.pgh.pa.us>
 <87y31oq9g6.fsf@news-spur.riddles.org.uk>
 <CA+hUKGJniUoFuC8vPJBKbMWNwvZo_wGQ8gVAZFCS068Rei9dzQ@mail.gmail.com>
 <3961.1564086915@!sss.pgh.pa.us>
 <CADT4RqBkkWEXr7saiFhwSptuYBAEU_e_XZxRD3o7GCSuk++Y9A@mail.gmail.com>
 <5560.1564668481@sss.pgh.pa.us>
 <20190801171951.pzpp5ywdn4pgqjzc@alap3.anarazel.de>
 <8331.1564682351@sss.pgh.pa.us>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <8331.1564682351@sss.pgh.pa.us>
Precedence: bulk

Hi,

On 2019-08-01 13:59:11 -0400, Tom Lane wrote:
> Andres Freund <andres@anarazel.de> writes:
> > When used and a symlink, could we resolve the symlink when determining
> > the timezone? When loading a timezone in the backend, not during
> > initdb. While that'd leave us with the instability, it'd at least would
> > help clients etc understand what the setting actually means?
> 
> The question here is what the string "localtime" means when it's in
> the timezone variable.

Right.


> I guess yes, we could install some show_hook for timezone that goes
> and looks to see if it can resolve what that means.  But that sure
> seems to me to be in you've-got-to-be-kidding territory.

Fair enough. I'm mildly worried that people will just carry their
timezone setting from one version's postgresql.conf to the next as they
upgrade.


> Especially since the platforms I've seen that do this tend to use hard
> links, so that it's questionable whether the pushups would accomplish
> anything at all.

Hm, debian's is a symlink (or rather a chain of):

$ ls -l /usr/share/zoneinfo/localtime
lrwxrwxrwx 1 root root 14 Jul  4 14:04 /usr/share/zoneinfo/localtime -> /etc/localtime

$ ls -l /etc/localtime
lrwxrwxrwx 1 root root 39 Jul 15 15:40 /etc/localtime -> /usr/share/zoneinfo/America/Los_Angeles

The system installed versions of postgres I have available all ended up
with timezone=localtime.

Not sure how long they've been symlinks. I randomly accessed a backup of
an older debian installation, from 2014, and there it's a file (with
link count 1).

But presumably upgrading would yield a postgresql.conf that still had
localtime, but localtime becoming a symlink.

Greetings,

Andres Freund