B.4. Date/Time Configuration Files
Since timezone abbreviations are not well standardized,
PostgreSQL provides a means to customize
the set of abbreviations accepted by the server. The
timezone_abbreviations run-time parameter
determines the active set of abbreviations. While this parameter
can be altered by any database user, the possible values for it
are under the control of the database administrator — they
are in fact names of configuration files stored in
.../share/timezonesets/ of the installation directory.
By adding or altering files in that directory, the administrator
can set local policy for timezone abbreviations.
timezone_abbreviations can be set to any file name
.../share/timezonesets/, if the file's name
is entirely alphabetic. (The prohibition against non-alphabetic
timezone_abbreviations prevents reading
files outside the intended directory, as well as reading editor
backup files and other extraneous files.)
A timezone abbreviation file can contain blank lines and comments
#. Non-comment lines must have one of
zone_abbreviation is just the abbreviation
being defined. An
offset is an integer giving
the equivalent offset in seconds from UTC, positive being east from
Greenwich and negative being west. For example, -18000 would be five
hours west of Greenwich, or North American east coast standard time.
D indicates that the zone name represents local
daylight-savings time rather than standard time.
time_zone_name can be given, referencing
a zone name defined in the IANA timezone database. The zone's definition
is consulted to see whether the abbreviation is or has been in use in
that zone, and if so, the appropriate meaning is used — that is,
the meaning that was currently in use at the timestamp whose value is
being determined, or the meaning in use immediately before that if it
wasn't current at that time, or the oldest meaning if it was used only
after that time. This behavior is essential for dealing with
abbreviations whose meaning has historically varied. It is also allowed
to define an abbreviation in terms of a zone name in which that
abbreviation does not appear; then using the abbreviation is just
equivalent to writing out the zone name.
Using a simple integer
offset is preferred
when defining an abbreviation whose offset from UTC has never changed,
as such abbreviations are much cheaper to process than those that
require consulting a time zone definition.
@INCLUDE syntax allows inclusion of another file in the
.../share/timezonesets/ directory. Inclusion can be nested,
to a limited depth.
@OVERRIDE syntax indicates that subsequent entries in the
file can override previous entries (typically, entries obtained from
included files). Without this, conflicting definitions of the same
timezone abbreviation are considered an error.
In an unmodified installation, the file
all the non-conflicting time zone abbreviations for most of the world.
provided for those regions: these files first include the
Default file and then add or modify abbreviations as needed.
For reference purposes, a standard installation also contains files
America.txt, etc, containing
information about every time zone abbreviation known to be in use
according to the IANA timezone database. The zone name
definitions found in these files can be copied and pasted into a custom
configuration file as needed. Note that these files cannot be directly
timezone_abbreviations settings, because of
the dot embedded in their names.
If an error occurs while reading the time zone abbreviation set, no new value is applied and the old set is kept. If the error occurs while starting the database, startup fails.
Time zone abbreviations defined in the configuration file override
non-timezone meanings built into PostgreSQL.
For example, the
Australia configuration file defines
SAT (for South Australian Standard Time). When this
file is active,
SAT will not be recognized as an abbreviation
If you modify files in
it is up to you to make backups — a normal database dump
will not include this directory.