Locale support refers to an application respecting cultural preferences regarding alphabets, sorting, number formatting, etc. LightDB 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.
Locale support is automatically initialized when a database
cluster is created using lt_initdb.
lt_initdb will initialize the database instance
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 instance 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
lt_initdb exactly which locale to use by
specifying the --locale option. For example:
lt_initdb --locale=sv_SE
This example for Unix systems sets the locale to Swedish
(sv) as spoken
in Sweden (SE). Other possibilities might include
en_US (U.S. English) and fr_CA (French
Canadian). If more than one character set can be used for a
locale then the specifications can take the form
language_territory.codeset. For example,
fr_BE.UTF-8 represents the French language (fr) as
spoken in Belgium (BE), with a UTF-8 character set
encoding.
What locales are available on your
system under what names depends on what was provided by the operating
system vendor and what was installed. On most Unix 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 certain aspects 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
lt_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
lt_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 name C, or equivalently
POSIX.
Some locale categories must have their values
fixed when the database is created. You can use different settings
for different databases, but once a database is created, you cannot
change them for that database anymore. LC_COLLATE
and LC_CTYPE are these categories. They affect
the sort order of indexes, so they must be kept fixed, or indexes on
text columns would become corrupt.
(But you can alleviate this restriction using collations, as discussed
in Section 22.2.)
The default values for these
categories are determined when lt_initdb is run, and
those values are used when new databases are created, unless
specified otherwise in the CREATE DATABASE command.
The other locale categories can be changed whenever desired
by setting the server configuration parameters
that have the same name as the locale categories (see Section 18.12.2 for details). The values
that are chosen by lt_initdb are actually only written
into the configuration file lightdb.conf to
serve as defaults when the server is started. If you remove these
assignments from lightdb.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.
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
(or 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.
To enable messages to be translated to the user's preferred language,
NLS must have been selected at build time
(configure --enable-nls). All other locale support is
built in automatically.
The locale settings influence the following SQL features:
Sort order in queries using ORDER BY or the standard
comparison operators on textual data
Pattern matching operators (LIKE, SIMILAR TO,
and POSIX-style regular expressions); locales affect both case
insensitive matching and the classification of characters by
character-class regular expressions
The ability to use indexes with LIKE clauses
The drawback of using locales other than C or
POSIX in LightDB 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 LightDB 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 12.10
for more information. Another approach is to create indexes using
the C collation, as discussed in
Section 22.2.
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 LightDB is actually using the locale
that you think it is. The LC_COLLATE and LC_CTYPE
settings are determined when a database is created, and cannot be
changed except by creating a new database. 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
LightDB'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 LightDB 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 51 or write to the developers' mailing list.