src/timezone/README

Timezone
========

This is a PostgreSQL adapted version of the timezone library from
http://www.iana.org/time-zones

The source code can be found at:

	ftp://ftp.iana.org/tz/releases/tzcode*.tar.gz

The code is currently synced with release 2010c.  There are many cosmetic
(and not so cosmetic) differences from the original tzcode library, but
diffs in the upstream version should usually be propagated to our version.

The data files under data/ are an exact copy of the latest data set from:

	ftp://ftp.iana.org/tz/releases/tzdata*.tar.gz

Since time zone rules change frequently in some parts of the world,
we should endeavor to update the data files before each PostgreSQL
release.

While the files under data/ can just be duplicated when updating, manual
effort is needed to update the time zone abbreviation lists under tznames/.
These need to be changed whenever new abbreviations are invented or the
UTC offset associated with an existing abbreviation changes.  To detect
if this has happened, after installing new files under data/ do
	make abbrevs.txt
which will produce a file showing all abbreviations that are in current
use according to the data/ files.  Compare this to known_abbrevs.txt,
which is the list that existed last time the tznames/ files were updated.
Update tznames/ as seems appropriate, then replace known_abbrevs.txt
in the same commit.

When there has been a new release of Windows (probably including Service
Packs), the list of matching timezones need to be updated. Run the
script in src/tools/win32tzlist.pl on a Windows machine running this new
release and apply any new timezones that it detects. Never remove any
mappings in case they are removed in Windows, since we still need to
match properly on the old version.
