src/timezone/README

Timezone
========

This is a PostgreSQL adapted version of the timezone library from:

	ftp://elsie.nci.nih.gov/pub/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://elsie.nci.nih.gov/pub/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.

At each update, we should check if time zone offsets have changed.
Just search for the current or previous year and see what has changed.
Sometimes a country changes its time zone offsets, for example Georgia
in 2004.  Just grepping in the zic database files for 2004 is enough to
spot such a change.  Then the files under tznames/ should be updated.

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.