[tz] What data should TZDB offer?

[Tom Lane]

John Hawkinson <jhawk at alum.mit.edu> writes:
> Tom Lane via tz <tz at iana.org> wrote on Sun,  6 Jun 2021
> at 13:31:06 EDT in <655997.1623000666 at sss.pgh.pa.us>:
>> I had a further thought about this: if we want to have both of these
>> principles (zone-per-country and stability of old data), then it would
>> make sense to insist that we don't create new per-country zones until
>> someone has done the research to fill in plausible old data back to
>> the LMT era for the proposed zone name.

> I don't think it's fair because the tz database needs to turn on a dime to reflect political changes that happen on rapid timescales. If a zone into two countries (whether by one of two previously-aligned countries changing their time zone rules, or by other political or even military mechanism) overnight, we need to push a new release out ASAP, we can't say, "oh, sorry, you can't have working time on your computers, we have to research the history, just suffer along for 6 months."

You're misunderstanding the context, I think.  If country X actually
changes their DST rules with minimal notice, then yeah, we'd have to
create a new zone and worry about correcting its old data later.
What I'm thinking about is how to handle the situation where X should
have its own zone according to the newly formulated zone-per-country
rule, but there is no post-1970 data divergence that would make it
necessary to have a separate zone according to other rules.  I do not
think that there need be any urgency about making that new zone come
into existence, especially not if that would certainly lead to the
need to change its pre-1970 data later.  So I don't buy that there's
any "fairness" argument.  What's unfair about asking somebody who
wants a quick change to do the legwork to support it?

			regards, tom lane