DST law changes in Fiji and Norfolk Island. Historical corrections
for Alberta, Austria, Belgium, British Columbia, Cambodia, Hong Kong,
Indiana (Perry County), Kaliningrad, Kentucky, Michigan, Norfolk
Island, South Korea, and Turkey.
DST law changes in Palestine and Metlakatla.
Historical corrections for Israel.
Etc/UCT is now a backward-compatibility link to Etc/UTC, instead
of being a separate zone that generates the abbreviation "UCT",
which nowadays is typically a typo. Postgres will still accept
"UCT" as an input zone name, but it won't output it.
DST law changes in Kazakhstan, Metlakatla, and São Tomé and Príncipe.
Kazakhstan's Qyzylorda zone is split in two, creating a new zone
Asia/Qostanay, as some areas did not change UTC offset.
Historical corrections for Hong Kong and numerous Pacific islands.
DST law changes in Chile, Fiji, and Russia (Volgograd).
Historical corrections for China, Japan, Macau, and North Korea.
Note: like the previous tzdata update, this involves a depressingly
large amount of semantically-meaningless churn in tzdata.zi. That
is a consequence of upstream's data compression method assigning
unstable abbreviations to DST rulesets. I complained about that
to them last time, and this version now uses an assignment method
that pays some heed to not changing abbreviations unnecessarily.
So hopefully, that'll be better going forward.
DST law changes in North Korea. Redefinition of "daylight savings" in
Ireland, as well as for some past years in Namibia and Czechoslovakia.
Additional historical corrections for Czechoslovakia.
With this change, the IANA database models Irish timekeeping as following
"standard time" in summer, and "daylight savings" in winter, so that the
daylight savings offset is one hour behind standard time not one hour
ahead. This does not change their UTC offset (+1:00 in summer, 0:00 in
winter) nor their timezone abbreviations (IST in summer, GMT in winter),
though now "IST" is more correctly read as "Irish Standard Time" not "Irish
Summer Time". However, the "is_dst" column in the pg_timezone_names view
will now be true in winter and false in summer for the Europe/Dublin zone.
Similar changes were made for Namibia between 1994 and 2017, and for
Czechoslovakia between 1946 and 1947.
So far as I can find, no Postgres internal logic cares about which way
tm_isdst is reported; in particular, since commit b2cbced9e we do not
rely on it to decide how to interpret ambiguous timestamps during DST
transitions. So I don't think this change will affect any Postgres
behavior other than the timezone-view outputs.
Discussion: https://postgr.es/m/30996.1525445902@sss.pgh.pa.us
DST law changes in Palestine and Antarctica (Casey Station). Historical
corrections for Portugal and its colonies, as well as Enderbury, Jamaica,
Turks & Caicos Islands, and Uruguay.
DST law changes in Brazil, Sao Tome and Principe. Historical corrections
for Bolivia, Japan, and South Sudan. The "US/Pacific-New" zone has been
removed (it was only a link to America/Los_Angeles anyway).
Traditionally IANA has distributed their timezone data in pure source
form, replete with extensive historical comments. As of release 2017c,
they've added a compact single-file format that omits comments and
abbreviates command keywords. This form is way shorter than the pure
source, even before considering its allegedly better compressibility.
Hence, let's distribute the data in that form rather than pure source.
I'm pushing this now, rather than at the next timezone database update,
so that it's easy to confirm that this data file produces compiled zic
output that's identical to what we were getting before.
Discussion: https://postgr.es/m/1915.1511210334@sss.pgh.pa.us
Tom Lane