[tz] Getting current tzdb version in use

Tom Lane tgl at sss.pgh.pa.us
Fri Jul 20 18:49:45 UTC 2018

Paul Eggert <eggert at cs.ucla.edu> writes:
> Tom Lane wrote:
>> FWIW, Postgres has already switched over from shipping the raw tzdb text
>> files in our tarball to shipping tzdata.zi, precisely because it's a lot
>> smaller and you get the same output after running it through zic.

> Thanks for letting me know. I have a version-related question about that.

> zishrink.awk currently avoids some optimizations (and thus generates a longer 
> file than it could) for compatibility with zic 2017b and earlier. I was thinking 
> of enabling those optimizations in a few months, on the theory that tzdata.zi is 
> a relatively new feature and anybody who's using it is also using a newer zic.

> So my question is: does "running it through zic" mean running tzdata.zi through 
> the system zic (which is not always present, and which may predate 2017b), or 
> does it mean running tzdata.zi through your own copy of zic?

We run it through our own copy of zic --- generally, that subsystem is
meant to support platforms that don't have tzdb at all, so we couldn't
really expect zic to be available either.  (On well-maintained platforms,
people typically configure Postgres to use the platform's copy of tzdb
not its own, whereupon updates are not our problem.)

We are somewhat more slothful about updating our copy of the tz code than
tz data, but all our currently-maintained release branches are currently
synced to tzcode 2018e, so it'd be no problem for us if you do something
that requires a current zic.  In general, anytime you guys do something
to the data that requires tzcode >= NN, we have to be sure we're up to NN
because of the possibility that platform copies of tzdb will get the
update almost immediately, whether or not we update our copy of the data.
So that tends to be a stronger forcing function than zic proper anyway.

Thanks for asking!

			regards, tom lane

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