Locale support refers to an application respecting
cultural preferences regarding alphabets, sorting, number
formatting, etc. PostgreSQL uses the standard ISO
C and POSIX-like locale facilities provided by the server operating
system. For additional information refer to the documentation of your
system.
Locale support is automatically initialized when a database
cluster is created using initdb.
initdb will initialize the database cluster
with the locale setting of its execution environment; so if your
system is already set to use the locale that you want in your
database cluster then there is nothing else you need to do. If
you want to use a different locale (or you are not sure which
locale your system is set to), you can tell
initdb exactly which locale you want with the
option --locale. For example:
$ initdb --locale=sv_SE
This example sets the locale to Swedish (sv) as spoken in
Sweden (SE). Other possibilities might be
en_US (U.S. English) and fr_CA (Canada,
French). If more than one character set can be useful for a locale
then the specifications look like this:
cs_CZ.ISO8859-2. What locales are available under what
names on your system depends on what was provided by the operating
system vendor and what was installed.
Occasionally it is useful to mix rules from several locales, e.g.,
use U.S. collation rules but Spanish messages. To support that, a
set of locale subcategories exist that control only a certain
aspect of the localization rules.
The category names translate into names of
initdb options to override the locale choice
for a specific category. For instance, to set the locale to
French Canadian, but use U.S. rules for formatting currency, use
initdb --locale=fr_CA --lc-monetary=en_US.
If you want the system to behave as if it had no locale support,
use the special locale C or POSIX.
The nature of some locale categories is that their value has to be
fixed for the lifetime of a database cluster. That is, once
initdb has run, you cannot change them anymore.
LC_COLLATE and LC_CTYPE are
those categories. They affect the sort order of indexes, so they
must be kept fixed, or indexes on text columns will become corrupt.
PostgreSQL enforces this by recording
the values of LC_COLLATE and LC_CTYPE that are
seen by initdb. The server automatically adopts
those two values when it is started.
The other locale categories can be changed as desired whenever the
server is started by setting the run-time configuration variables
that have the same name as the locale categories (see Section 3.4 for details). The defaults that are
chosen by initdb are actually only written into
the configuration file postgresql.conf to
serve as defaults when the server is started. If you delete the
assignments from postgresql.conf then the
server will inherit the settings from the execution environment.
Note that the locale behavior of the server is determined by the
environment variables seen by the server, not by the environment
of any client. Therefore, be careful to configure the correct locale settings
before starting the server. A consequence of this is that if
client and server are set up to different locales, messages may
appear in different languages depending on where they originated.
Note: When we speak of inheriting the locale from the execution
environment, this means the following on most operating systems:
For a given locale category, say the collation, the following
environment variables are consulted in this order until one is
found to be set: LC_ALL, LC_COLLATE
(the variable corresponding to the respective category),
LANG. If none of these environment variables are
set then the locale defaults to C.
Some message localization libraries also look at the environment
variable LANGUAGE which overrides all other locale
settings for the purpose of setting the language of messages. If
in doubt, please refer to the documentation of your operating
system, in particular the
gettext manual
page, for more information.
To enable messages translated to the user's preferred language,
the --enable-nls option must be used. This
option is independent of the other locale support.
Locale support influences in particular the following features:
Sort order in ORDER BY queries.
The to_char family of functions
The LIKE and ~ operators for pattern
matching
The only severe drawback of using the locale support in
PostgreSQL is its speed. So use locale only if you
actually need it. It should be noted in particular that selecting
a non-C locale disables index optimizations for LIKE and
~ operators, which can make a huge difference in the
speed of searches that use those operators.
If locale support doesn't work in spite of the explanation above,
check that the locale support in your operating system is correctly configured.
To check whether a given locale is installed and functional you
can use Perl, for example. Perl has also support
for locales and if a locale is broken perl -v will
complain something like this:
$ export LC_CTYPE='not_exist'
$ perl -v
perl: warning: Setting locale failed.
perl: warning: Please check that your locale settings:
LC_ALL = (unset),
LC_CTYPE = "not_exist",
LANG = (unset)
are supported and installed on your system.
perl: warning: Falling back to the standard locale ("C").
Check that your locale files are in the right location. Possible
locations include: /usr/lib/locale (Linux,
Solaris), /usr/share/locale (Linux),
/usr/lib/nls/loc (DUX 4.0). Check the locale
man page of your system if you are not sure.
Check that PostgreSQL is actually using the locale that
you think it is. LC_COLLATE and LC_CTYPE settings are
determined at initdb time and cannot be changed without
repeating initdb. Other locale settings including
LC_MESSAGES and LC_MONETARY are determined by the
environment the postmaster is started in, and can be changed with a simple
postmaster restart. You can check the LC_COLLATE and
LC_CTYPE settings of
a database with the contrib/pg_controldata utility program.
The directory src/test/locale contains a test suite
for PostgreSQL's locale support.
Client applications that handle server-side errors by parsing the
text of the error message will obviously have problems when the
server's messages are in a different language. If you create such
an application you need to devise a plan to cope with this
situation. The embedded SQL interface (ecpg) is
also affected by this problem. It is currently recommended that
servers interfacing with ecpg applications be
configured to send messages in English.
Maintaining catalogs of message translations requires the on-going
efforts of many volunteers that want to see
PostgreSQL speak their preferred language well.
If messages in your language is currently not available or fully
translated, your assistance would be appreciated. If you want to
help, refer to the Developer's Guide or write to the
developers' mailing list.
