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22.1. Locale Support

Locale support refers to an application respecting cultural preferences regarding alphabets, sorting, number formatting, etc. PostgreSQL uses the standard ISO C and POSIX locale facilities provided by the server operating system. For additional information refer to the documentation of your system.

22.1.1. Overview

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 by default, 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 instruct initdb exactly which locale to use by specifying the --locale option. 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 (French Canadian). 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. (On most systems, the command locale -a will provide a list of available locales.)

Occasionally it is useful to mix rules from several locales, e.g., use English collation rules but Spanish messages. To support that, a set of locale subcategories exist that control only a certain aspect of the localization rules:

LC_COLLATE String sort order
LC_CTYPE Character classification (What is a letter? Its upper-case equivalent?)
LC_MESSAGES Language of messages
LC_MONETARY Formatting of currency amounts
LC_NUMERIC Formatting of numbers
LC_TIME Formatting of dates and times
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 running by setting the run-time configuration variables that have the same name as the locale categories (see Section 18.10.2 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 these assignments from postgresql.conf then the server will inherit the settings from its 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 in different locales, messages might 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 documentation about gettext, for more information.

To enable messages to be translated to the user's preferred language, NLS must have been enabled at build time. This choice is independent of the other locale support.

22.1.2. Behavior

The locale settings influence the following SQL features:

  • Sort order in queries using ORDER BY on textual data

  • The ability to use indexes with LIKE clauses

  • The upper, lower, and initcap functions

  • The to_char family of functions

The drawback of using locales other than C or POSIX in PostgreSQL is its performance impact. It slows character handling and prevents ordinary indexes from being used by LIKE. For this reason use locales only if you actually need them.

As a workaround to allow PostgreSQL to use indexes with LIKE clauses under a non-C locale, several custom operator classes exist. These allow the creation of an index that performs a strict character-by-character comparison, ignoring locale comparison rules. Refer to Section 11.9 for more information.

22.1.3. Problems

If locale support doesn't work according to the explanation above, check that the locale support in your operating system is correctly configured. To check what locales are installed on your system, you can use the command locale -a if your operating system provides it.

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 initially determined by the environment the server is started in, but can be changed on-the-fly. You can check the active locale settings using the SHOW command.

The directory src/test/locale in the source distribution 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. Authors of such applications are advised to make use of the error code scheme instead.

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 are currently not available or not fully translated, your assistance would be appreciated. If you want to help, refer to Chapter 47 or write to the developers' mailing list.

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