[tz] Irish Standard Time vs Irish Summer Time

John Hawkinson jhawk at MIT.EDU
Sat Jan 20 16:08:43 UTC 2018

Catching up on this thread, this one item jumped out at me:

Philip Paeps <philip at trouble.is> wrote on Fri, 19 Jan 2018
at 06:44:15 +0100 in <20180119054415.GF75764 at rincewind.trouble.is>:

> Given the number of things this break, I would suggest backing the
> change out for now but pointing out in NEWS that it will come back
> say one year from now.

We need to be clear that in the world of timezone software, with complex downstream dependencies and embedded devices and mobile devices with weird update strategies that take data but not code, a year is *not* a long period of time. It's not long for tzdata, but it is far shorter for code.

A year is a short period of time. It's not enough time for product life cycles, for deploying code changes reliably, etc.

I'm not sure what the right amount of time is, but if we think a year is short, we are fooling ourselves.

I also concur that there have been a lot of destabilizing changes in the tz database in recent years and that they seem to me like a not-very-good idea. Many of these changes would be fine if we had been starting from scratch and it was the first release, but we're not, and so they are not.

(Relatively unimportantly, I particularly wonder at the effect of changes that adjust the historical rules of some zones from long ago, as we decide Shanks was wrong, etc. If anyone in such a zone had files in their filesystem with dates that far back, they would see weird churn and and odd changes relative to more recent timestamps, and I wonder at the wisdom of making those changes.)

--jhawk at mit.edu
  John Hawkinson

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