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10 MySQL Server Functions

This chapter describes the languages MySQL supports, how sorting works in MySQL, and how to add new character sets to MySQL. You will also find information about maximum table sizes in this chapter.

10.1 What Languages Are Supported by MySQL?

mysqld can issue error messages in the following languages: Czech, Danish, Dutch, English (the default), Estonian, French, German, Greek, Hungarian, Italian, Japanese, Korean, Norwegian, Norwegian-ny, Polish, Portuguese, Romanian, Russian, Slovak, Spanish, and Swedish.

To start mysqld with a particular language, use either the --language=lang or -L lang options. For example:

shell> mysqld --language=swedish

or:

shell> mysqld --language=/usr/local/share/swedish

Note that all language names are specified in lowercase.

The language files are located (by default) in `mysql_base_dir/share/LANGUAGE/'.

To update the error message file, you should edit the `errmsg.txt' file and execute the following command to generate the `errmsg.sys' file:

shell> comp_err errmsg.txt errmsg.sys

If you upgrade to a newer version of MySQL, remember to repeat your changes with the new `errmsg.txt' file.

10.1.1 The Character Set Used for Data and Sorting

By default, MySQL uses the ISO-8859-1 (Latin1) character set with sorting according to Swedish/Finnish. This is the character set suitable in the USA and western Europe.

All standard MySQL binaries are compiled with --with-extra-charsets=complex. This will add code to all standard programs to be able to handle latin1 and all multi-byte character sets within the binary. Other character sets will be loaded from a character-set definition file when needed.

The character set determines what characters are allowed in names and how things are sorted by the ORDER BY and GROUP BY clauses of the SELECT statement.

You can change the character set with the --default-character-set option when you start the server. The character sets available depend on the --with-charset=charset and --with-extra-charset= list-of-charset | complex | all options to configure, and the character set configuration files listed in `SHAREDIR/charsets/Index'. See section 4.7.3 Typical configure Options.

If you change the character set when running MySQL (which may also change the sort order), you must run myisamchk -r -q on all tables. Otherwise your indexes may not be ordered correctly.

When a client connects to a MySQL server, the server sends the default character set in use to the client. The client will switch to use this character set for this connection.

One should use mysql_real_escape_string() when escaping strings for a SQL query. mysql_real_escape_string() is identical to the old mysql_escape_string() function, except that it takes the MYSQL connection handle as the first parameter.

If the client is compiled with different paths than where the server is installed and the user who configured MySQL didn't included all character sets in the MySQL binary, one must specify for the client where it can find the additional character sets it will need if the server runs with a different character set than the client.

One can specify this by putting in a MySQL option file:

[client]
character-sets-dir=/usr/local/mysql/share/mysql/charsets

where the path points to where the dynamic MySQL character sets are stored.

One can force the client to use specific character set by specifying:

[client]
default-character-set=character-set-name

but normally this is never needed.

10.1.2 Adding a New Character Set

To add another character set to MySQL, use the following procedure.

Decide if the set is simple or complex. If the character set does not need to use special string collating routines for sorting and does not need multi-byte character support, it is simple. If it needs either of those features, it is complex.

For example, latin1 and danish are simple charactersets while big5 or czech are complex character sets.

In the following section, we have assumed that you name your character set MYSET.

For a simple character set do the following:

  1. Add MYSET to the end of the `sql/share/charsets/Index' file Assign an unique number to it.
  2. Create the file `sql/share/charsets/MYSET.conf'. (You can use `sql/share/charsets/latin1.conf' as a base for this). The syntax for the file very simple: See section 10.1.3 The character definition arrays.
  3. Add the character set name to the CHARSETS_AVAILABLE and COMPILED_CHARSETS lists in configure.in.
  4. Reconfigure, recompile, and test.

For a complex character set do the following:

  1. Create the file `strings/ctype-MYSET.c' in the MySQL source distribution.
  2. Add MYSET to the end of the `sql/share/charsets/Index' file. Assign an unique number to it.
  3. Look at one of the existing `ctype-*.c' files to see what needs to be defined, for example `strings/ctype-big5.c'. Note that the arrays in your file must have names like ctype_MYSET, to_lower_MYSET, and so on. This corresponds to the arrays in the simple character set. See section 10.1.3 The character definition arrays. For a complex character set
  4. Near the top of the file, place a special comment like this:
    /*
     * This comment is parsed by configure to create ctype.c,
     * so don't change it unless you know what you are doing.
     *
     * .configure. number_MYSET=MYNUMBER
     * .configure. strxfrm_multiply_MYSET=N
     * .configure. mbmaxlen_MYSET=N
     */
    
    The configure program uses this comment to include the character set into the MySQL library automatically. The strxfrm_multiply and mbmaxlen lines will be explained in the following sections. Only include them if you the string collating functions or the multi-byte character set functions, respectively.
  5. You should then create some of the following functions: See section 10.1.4 String Collating Support.
  6. Add the character set name to the CHARSETS_AVAILABLE and COMPILED_CHARSETS lists in configure.in.
  7. Reconfigure, recompile, and test.

The file `sql/share/charsets/README' includes some more instructions.

If you want to have the character set included in the MySQL distribution, mail a patch to internals@lists.mysql.com.

10.1.3 The character definition arrays

to_lower[] and to_upper[] are simple arrays that hold the lowercase and uppercase characters corresponding to each member of the character set. For example:

to_lower['A'] should contain 'a'
to_upper['a'] should contain 'A'

sort_order[] is a map indicating how characters should be ordered for comparison and sorting purposes. For many character sets, this is the same as to_upper[] (which means sorting will be case insensitive). MySQL will sort characters based on the value of sort_order[character]. For more complicated sorting rules, see the discussion of string collating below. See section 10.1.4 String Collating Support.

ctype[] is an array of bit values, with one element for one character. (Note that to_lower[], to_upper[], and sort_order[] are indexed by character value, but ctype[] is indexed by character value + 1. This is an old legacy to be able to handle EOF.)

You can find the following bitmask definitions in `m_ctype.h':

#define _U      01      /* Uppercase */
#define _L      02      /* Lowercase */
#define _N      04      /* Numeral (digit) */
#define _S      010     /* Spacing character */
#define _P      020     /* Punctuation */
#define _C      040     /* Control character */
#define _B      0100    /* Blank */
#define _X      0200    /* heXadecimal digit */

The ctype[] entry for each character should be the union of the applicable bitmask values that describe the character. For example, 'A' is an uppercase character (_U) as well as a hexadecimal digit (_X), so ctype['A'+1] should contain the value:

_U + _X = 01 + 0200 = 0201

10.1.4 String Collating Support

If the sorting rules for your language are too complex to be handled with the simple sort_order[] table, you need to use the string collating functions.

Right now the best documentation on this is the character sets that are already implemented. Look at the big5, czech, gbk, sjis, and tis160 character sets for examples.

You must specify the strxfrm_multiply_MYSET=N value in the special comment at the top of the file. N should be set to the maximum ratio the strings may grow during my_strxfrm_MYSET (it must be a positive integer).

10.1.5 Multi-byte Character Support

If your want to add support for a new character set that includes multi-byte characters, you need to use the multi-byte character functions.

Right now the best documentation on this is the character sets that are already implemented. Look at the euc_kr, gb2312, gbk, sjis and ujis character sets for examples. These are implemented in the ctype-'charset'.c files in the `strings' directory.

You must specify the mbmaxlen_MYSET=N value in the special comment at the top of the source file. N should be set to the size in bytes of the largest character in the set.

10.2 How Big MySQL Tables Can Be

MySQL Version 3.22 has a 4G limit on table size. With the new MyISAM in MySQL Version 3.23 the maximum table size is pushed up to 8 million terabytes (2 ^ 63 bytes).

Note, however, that operating systems have their own file size limits. Here are some examples:

Operating System File Size Limit
Linux-Intel 32 bit 2G, 4G or more, depends on Linux version
Linux-Alpha 8T (?)
Solaris 2.5.1 2G (possible 4G with patch)
Solaris 2.6 4G
Solaris 2.7 Intel 4G
Solaris 2.7 ULTRA-SPARC 8T (?)

On Linux 2.2 you can get bigger tables than 2G by using the LFS patch for the ext2 file system. On Linux 2.4 there exists also patches for ReiserFS to get support for big files.

This means that the table size for MySQL is normally limited by the operating system.

By default, MySQL tables have a maximum size of about 4G. You can check the maximum table size for a table with the SHOW TABLE STATUS command or with the myisamchk -dv table_name. See section 7.28 SHOW Syntax.

If you need bigger tables than 4G (and your operating system supports this), you should set the AVG_ROW_LENGTH and MAX_ROWS parameter when you create your table. See section 7.7 CREATE TABLE Syntax. You can also set these later with ALTER TABLE. See section 7.8 ALTER TABLE Syntax.

If your big table is going to be read-only, you could use myisampack to merge and compress many tables to one. myisampack usually compresses a table by at least 50%, so you can have, in effect, much bigger tables. See section 15.12 The MySQL Compressed Read-only Table Generator.

You can go around the operating system file limit for MyISAM data files by using the RAID option. See section 7.7 CREATE TABLE Syntax.

Another solution can be the included MERGE library, which allows you to handle a collection of identical tables as one. See section 8.2 MERGE Tables.


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