[tz] DST ends 2040 in Oracle database

Paul Eggert eggert at cs.ucla.edu
Thu Jan 24 18:30:59 UTC 2019

On 1/24/19 2:05 AM, Joachim Damm wrote:
> we found one issue in the Oracle database that DST calculation is 
> wrong from 2040 and beyond.

Which DST calculation, exactly, and what are the incorrect and correct 

Perhaps you're thinking about Brazil, Iran, or Morocco. In these 
countries DST rules are so complex that they cannot be expressed in 
closed form in the tzdb notation, so tzdb lists rules explicitly for 
each year. Eventually this list has to stop, though, as the database and 
its maintainers' patience are finite. For Brazil and Morocco the list of 
exact predictions stops after 2037; for Iran, 2087.

Brazil and Morocco keep changing their DST rules, so any prediction past 
this year (much less past 2037) is dubious anyway. In contrast, Iran's 
rules have been stable since 2008, so I extended its exact prediction to 
2087; there is some technical confusion about how to interpret Iran's 
rules after that, and even Iran is likely to change its rules before 2087.

If there's a real need to predict past 2037, what is the need and how 
far does it really go?

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