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><A
NAME="DATETIME-CONFIG-FILES"
>B.3. Date/Time Configuration Files</A
></H1
><P
> Since timezone abbreviations are not well standardized,
<SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> provides a means to customize
the set of abbreviations accepted by the server. The
<A
HREF="runtime-config-client.html#GUC-TIMEZONE-ABBREVIATIONS"
>timezone_abbreviations</A
> 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
<TT
CLASS="FILENAME"
>.../share/timezonesets/</TT
> of the installation directory.
By adding or altering files in that directory, the administrator
can set local policy for timezone abbreviations.
</P
><P
> <TT
CLASS="VARNAME"
>timezone_abbreviations</TT
> can be set to any file name
found in <TT
CLASS="FILENAME"
>.../share/timezonesets/</TT
>, if the file's name
is entirely alphabetic. (The prohibition against non-alphabetic
characters in <TT
CLASS="VARNAME"
>timezone_abbreviations</TT
> prevents reading
files outside the intended directory, as well as reading editor
backup files and other extraneous files.)
</P
><P
> A timezone abbreviation file can contain blank lines and comments
beginning with <TT
CLASS="LITERAL"
>#</TT
>. Non-comment lines must have one of
these formats:
</P><PRE
CLASS="SYNOPSIS"
><TT
CLASS="REPLACEABLE"
><I
>zone_abbreviation</I
></TT
> <TT
CLASS="REPLACEABLE"
><I
>offset</I
></TT
>
<TT
CLASS="REPLACEABLE"
><I
>zone_abbreviation</I
></TT
> <TT
CLASS="REPLACEABLE"
><I
>offset</I
></TT
> D
<TT
CLASS="REPLACEABLE"
><I
>zone_abbreviation</I
></TT
> <TT
CLASS="REPLACEABLE"
><I
>time_zone_name</I
></TT
>
@INCLUDE <TT
CLASS="REPLACEABLE"
><I
>file_name</I
></TT
>
@OVERRIDE</PRE
><P>
</P
><P
> A <TT
CLASS="REPLACEABLE"
><I
>zone_abbreviation</I
></TT
> is just the abbreviation
being defined. An <TT
CLASS="REPLACEABLE"
><I
>offset</I
></TT
> 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.
<TT
CLASS="LITERAL"
>D</TT
> indicates that the zone name represents local
daylight-savings time rather than standard time.
</P
><P
> Alternatively, a <TT
CLASS="REPLACEABLE"
><I
>time_zone_name</I
></TT
> 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.
</P
><DIV
CLASS="TIP"
><BLOCKQUOTE
CLASS="TIP"
><P
><B
>Tip: </B
> Using a simple integer <TT
CLASS="REPLACEABLE"
><I
>offset</I
></TT
> 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.
</P
></BLOCKQUOTE
></DIV
><P
> The <TT
CLASS="LITERAL"
>@INCLUDE</TT
> syntax allows inclusion of another file in the
<TT
CLASS="FILENAME"
>.../share/timezonesets/</TT
> directory. Inclusion can be nested,
to a limited depth.
</P
><P
> The <TT
CLASS="LITERAL"
>@OVERRIDE</TT
> 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.
</P
><P
> In an unmodified installation, the file <TT
CLASS="FILENAME"
>Default</TT
> contains
all the non-conflicting time zone abbreviations for most of the world.
Additional files <TT
CLASS="FILENAME"
>Australia</TT
> and <TT
CLASS="FILENAME"
>India</TT
> are
provided for those regions: these files first include the
<TT
CLASS="LITERAL"
>Default</TT
> file and then add or modify abbreviations as needed.
</P
><P
> For reference purposes, a standard installation also contains files
<TT
CLASS="FILENAME"
>Africa.txt</TT
>, <TT
CLASS="FILENAME"
>America.txt</TT
>, 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
referenced as <TT
CLASS="VARNAME"
>timezone_abbreviations</TT
> settings, because of
the dot embedded in their names.
</P
><DIV
CLASS="NOTE"
><BLOCKQUOTE
CLASS="NOTE"
><P
><B
>Note: </B
> 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.
</P
></BLOCKQUOTE
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>Caution</B
></TD
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><P
> Time zone abbreviations defined in the configuration file override
non-timezone meanings built into <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
>.
For example, the <TT
CLASS="FILENAME"
>Australia</TT
> configuration file defines
<TT
CLASS="LITERAL"
>SAT</TT
> (for South Australian Standard Time). When this
file is active, <TT
CLASS="LITERAL"
>SAT</TT
> will not be recognized as an abbreviation
for Saturday.
</P
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></TD
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><P
> If you modify files in <TT
CLASS="FILENAME"
>.../share/timezonesets/</TT
>,
it is up to you to make backups — a normal database dump
will not include this directory.
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