[tz] Why 2021b needed to be issued

[Paul Eggert]

Since 2013 I've been patching tzdb by replacing Zones with Links when 
Links suffice according to the guidelines. These patches have not 
affected timestamps after 1970. I've been doing this gradually. The 
changes have worked without significant incident, partly because end 
users generally don't care about pre-1970 timestamps, and partly because 
the few users who do care (astrologers, mostly) know or should know that 
the pre-1970 Zone data entries are often wrong and even when right are 
typically grossly inadequate for realistic use outside the named 
location - this is partly why any focus on pre-1970 is out of scope for 
tzdb.

Preparing all these patches has been a big enough job that I've been 
doing it gradually since I have limited time. This process was discussed 
on the list before it began, and although there was some objection, a 
consensus to move towards these goals was reached at the time. Most of 
this job was done before 2021a came out.

The main difference in this round of patches, is that I had aimed to 
complete the job, in response to a user query raising equity concerns in 
2021a. It is clear that the 2021a setup was not sustainable in the long 
term, if equity is a goal.

Completing the job generated larger patches than usual, and the patches' 
size triggered concern that they held too many changes all at once. 
Also, the patches' effects on pre-1970 timestamps in (for example) 
Norway and Sweden have triggered concerns, much more so than similar 
changes made (for example) to Angola and Congo in tzdb 2014g.

My own view is that we've done this before, many times, it hasn't been a 
problem in practice, and it's way past time to address the equity 
concerns as they have a good chance to really bite this project and its 
repackagers in the future.

It's a bad look for us that so much concern about Norway and Sweden has 
appeared on this mailing list, even though hardly anybody seems to have 
cared about Angola and Congo. It'll be an even worse look if we ignore 
this issue weeks, months or even years after it's been made clear to us.

I wrote, tested and published several concrete suggestions addressing 
the fairness problem. In the months since May when the fairness problem 
was discovered and objections to my proposed fixes were raised, no other 
concrete fix addressing both of these concerns has been implemented or 
tested, and all other suggestions made so far would have required 
significant work, if they would have worked at all, or would have caused 
more data churn than what I proposed.

I realize that there are valid concerns about installing too many of 
these patches at once, so 2021b affects only nine Zones instead of the 
thirty-odd Zones in my May proposal. The idea is to do further patch 
sets in not-too-distant-future releases, so that the job can finally be 
finished.

I also recognize that there are other forms of equity and fairness that 
should be considered, perhaps along with alternative technical solutions 
to the problems these patches address.

With all this in mind, issuing 2021b now is a significant step toward 
equity in tzdb. It will let us say that we are moving toward a fair 
process, and will give us the opportunity and motivation to improve on 
that process and to address and balance the various other concerns that 
have recently appeared on the mailing list.