tz database community up in arms over proposals to merge certain time zones

Handbags at 12 o'clock! Er, is that with or without daylight saving?


The time zone database hosted at the Internet Assigned Numbers Authority (IANA) has been updated following threats, earlier this year, of a fork over a proposal to merge time zones.

The update, the 2021b release of the tz code and date, was published over the weekend and omits some, but not all, of the issues that have caused concern in the project's mailing list.

The tz database is a hugely important resource that contains information on the world's time zones. It also attempts to keep track of historical changes since 1970. Its usage is relatively straightforward; a time zone has an offset from UTC and a set of rules governing daylight saving time (should it apply).

The system gets regular updates, the last being 2021a. These do not usually generate drama – 2021a, for example, tweaked timestamps for South Sudan.

However, a proposal to merge multiple regions that have had the same data post-1970 into a single time zone has been met with controversy amid fears that an ID cull could result in pre-1970 data becoming difficult to get hold of – as well as causing backwards-compatibility issues.

In a nutshell, put "Europe/Berlin" or "Europe/Oslo" with a pre-1970 date into the system, and out will come an answer. But the answer will be different for each option as there was a time when the two zones were different. However, as they've been the same for the past 50+ years, the proposal was to have "Europe/Oslo" simply be an alias of "Europe/Berlin" – meaning that Oslo's pre-1970 data would be effectively replaced by Berlin's.

"Why can Berlin keep its status and full history, but Oslo gets effectively deleted?" asked Java developer and maintainer of the Joda-Time classes Stephen Colebourne. "The answer is that Berlin has the greater population."

"The project leader," Colebourne told The Register, "is trying to force through a merger of time zones affecting timestamps pre-1970. Data that has been present in the database for many years is to be effectively removed."

Describing the rationale for the move as "extremely limited," Colebourne went on to say: "No consideration is being taken of the big impacts on downstream systems – Joda-Time is particularly affected because of the way it handles links as full aliases.

"If a Joda-Time user were to adopt the proposed release, then it would no longer be possible to hold a time zone ID for Oslo, Stockholm or Amsterdam in memory – a catastrophic outcome."

The patch itself was proposed some months ago, and controversy has rumbled on ever since. Aside from a wholesale reversion of the patch, Colebourne suggested alternative approaches back in June before suggesting a fork in order to keep the time zone data as it was before.

The protests of Colebourne and other users have not completely fallen on deaf ears, and primary tz coordinator Paul Eggert announced the 2021b release over the weekend with some of the changes absent. The clock had been ticking due to daylight saving time observance being dropped in Samoa.

However, as well as changes for Samoa and Jordan, some merging of time zones still occurred, although the announcement noted "it omits most proposed changes that merged all Zones agreeing since 1970, as concerns were raised about doing too many of these changes at once."

The Register contacted Eggert for his take on the furore, but he preferred not to make a comment.

Eggert's announcement said of the merge: "This is part of a process that has been ongoing since 2013.

"This does not affect post-1970 timestamps, and timezone historians who build with 'make PACKRATDATA=backzone' should see no changes to pre-1970 timestamps."

As for Colebourne, he admitted that the battle was lost for now and blogged: "Tonight 9 of the 30 changes have been included in release 2021b. These are not the ones affecting Europe.

"Stay tuned as I try and work out how best to resolve this completely unecessary [sic] drama." ®

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