John Hawkinson <jhawk@alum.mit.edu> writes:
Tom Lane via tz <tz@iana.org> wrote on Sun, 6 Jun 2021 at 13:31:06 EDT in <655997.1623000666@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