Character Set Configuration </collation> 10.14.4.3 Diagnostics During Index.xml Parsing 10.15 Character Set Configuration The MySQL server generates diagnostics when it finds problems while parsing the  Index.xml  file: •Unknown tags are written to the error log. For example, the following message results if a collation definition contains a  <aaa>  tag: •If collation initialization is not possible, the server reports an “Unknown collation”  error, and also generates warnings explaining the problems, such as in the previous example. In other cases, when a collation description is generally correct but contains some unknown tags, the collation is initialized and is available for use. The unknown parts are ignored, but a warning is generated in the error log. •Problems with collations generate warnings that clients can display with  SHOW WARNINGS . Suppose that a reset rule contains an expansion longer than the maximum supported length of 6 characters: An attempt to use the collation produces warnings: The MySQL server has a compiled-in default character set and collation. To change these defaults, use the  --character-set-server  and  --collation-server  options when you start the server. See Section 5.1.7, “Server Command Options” . The collation must be a legal collation for the default character set. To determine which collations are available for each character set, use the  SHOW COLLATION statement or query the  INFORMATION_SCHEMA COLLATIONS  table. If you try to use a character set that is not compiled into your binary, you might run into the following problems: •If your program uses an incorrect path to determine where the character sets are stored (which is typically the  share/mysql/charsets  or  share/charsets  directory under the MySQL installation directory), this can be fixed by using the  --character-sets-dir  option when you run the program. For example, to specify a directory to be used by MySQL client programs, list it in the  [client]  group of your option file. The examples given here show what the setting might look like for Unix or Windows, respectively: •If the character set is a complex character set that cannot be loaded dynamically, you must recompile the program with support for the character set. [Warning] Buffered warning: Unknown LDML tag: ’charsets/charset/collation/rules/aaa’ <reset>abcdefghi</reset> <i>x</i> mysql>  SELECT _utf8’test’ COLLATE utf8_test_ci; ERROR 1273 (HY000): Unknown collation: ’utf8_test_ci’ mysql>  SHOW WARNINGS; +---------+------+----------------------------------------+ | Level | Code | Message | +---------+------+----------------------------------------+ | Error | 1273 | Unknown collation: ’utf8_test_ci’ | | Warning | 1273 | Expansion is too long at ’abcdefghi=x’ | +---------+------+----------------------------------------+ [client] character-sets-dir=/usr/local/mysql/share/mysql/charsets [client] character-sets-dir="C:/Program Files/MySQL/MySQL Server 8.0/share/charsets" 2004