[tz] Getting current tzdb version in use

Paul Eggert eggert at cs.ucla.edu
Fri Jul 20 18:04:43 UTC 2018

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? If the former, then 
I suppose we should wait a few years before adding those optimizations to 
zishrink.awk. If the latter, then I hope we can shrink tzdata.zi a bit in a few 
months rather than waiting until 2022.

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