On 10/05/18 19:57, Adriano dos Santos Fernandes wrote:
I can give more examples of problems which NOT knowing which rule set
was used to create the 'international' timetable when local DST times
are changed at short notice ... TZDist is intended to prevent this
problem, but since there are no active sources we are still stuck with
the miss-match of data between different OS's and system.
if you want to work with fixed rules even when they change, you should
have specialized treatment of the data. It's not difficult.
Yes you drop 'offset' on timestamps and add a properly managed
management of the timezone rules as a second column.
Store your data using the displacement syntax ± HH:MM and add the
region name to another column.
THAT is what is so badly broken! But in addition to timezone rule sets,
mapping what region is using what rule set is another table of information!
No other database engine is maintaining various versions at the same
time. Fortunately.
Which is why historic data is now so badly broken! And since other
databases don't even handle timezone rules, but simply add offsets then
pretend they do timezone management. AT the end of the day, even if you
don't agree that some way of identifying WHICH current set of rules are
being used you have to have some way of adding new timezone idents if TZ
needs to create them ... without having to recompile all the programs
that use that data!
While historic changes to the TZ information is probably now irrelevant
so nobody bothered making a note of the version of rules used at the
time, moving forward, if you ARE normalizing data to UTC, then every
change of TZ rules needs some mechanism to at least flag that existing
data may be compromised? There are only a very small number of changes
to the rule sets each year, but they are likely to affect current stored
data. Simply pretending the problem does not exist - as other databases
do - should not be acceptable these days.
--
Lester Caine - G8HFL
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