MYSQL官方提供的免费手册中就有。 5.1.4. Server System Variables The MySQL server maintains many system variables that indicate how it is configured. Each system variable has a default value. System variables can be set at server startup using options on the command line or in an option file. Most of them can be changed dynamically while the server is running by means of the SET statement, which enables you to modify operation of the server without having to stop and restart it. You can refer to system variable values in expressions. There are several ways to see the names and values of system variables: To see the values that a server will use based on its compiled-in defaults and any option files that it reads, use this command: mysqld --verbose --helpTo see the values that a server will use based on its compiled-in defaults, ignoring the settings in any option files, use this command: mysqld --no-defaults --verbose --helpTo see the current values used by a running server, use the SHOW VARIABLES statement. This section provides a description of each system variable. Variables with no version indicated are present in all MySQL 5.4 releases. For historical information concerning their implementation, please see http://www.mysql.com/products/enterprise//5.0/en/, and http://www.mysql.com/products/enterprise//4.1/en/. The following table lists all available system variables: Table 5.2. System Variable SummaryName Cmd-Line Option file System Var Var Scope Dynamic auto_increment_increment Yes Yes Yes Both Yes auto_increment_offset Yes Yes Yes Both Yes autocommit Yes Session Yes automatic_sp_privileges Yes Global Yes back_log Yes Yes Yes Global No basedir Yes Yes Yes Global No big-tables Yes Yes Yes - Variable: big_tables Yes Session Yes binlog_cache_size Yes Yes Yes Global Yes binlog-format Yes Yes Yes - Variable: binlog_format Yes Both Yes bulk_insert_buffer_size Yes Yes Yes Both Yes character_set_client Yes Both Yes character_set_connection Yes Both Yes character_set_database[a] Yes Both Yes character-set-filesystem Yes Yes Yes - Variable: character_set_filesystem Yes Both Yes character_set_results Yes Both Yes character-set-server Yes Yes Yes - Variable: character_set_server Yes Both Yes character_set_system Yes Global No character-sets-dir Yes Yes No - Variable: character_sets_dir Yes Global No collation_connection Yes Both Yes
key_buffer = 16M $$$:key_buffer是用于索引块的缓冲区大小，增加它可得到更好处理的索引(对所有读和多重写)。对于内存在4GB左右的服务器该参数可设置为256M或384M。注意：该参数值设置的过大反而会是服务器整体效率降低！
max_allowed_packet = 16M $$$:包或任何生成的/中间字符串的最大大小。
thread_stack = 192K
thread_cache_size = 8 $$$:缓存可重用的线程数
5.1.4. Server System Variables
The MySQL server maintains many system variables that indicate how it is configured. Each system variable has a default value. System variables can be set at server startup using options on the command line or in an option file. Most of them can be changed dynamically while the server is running by means of the SET statement, which enables you to modify operation of the server without having to stop and restart it. You can refer to system variable values in expressions. There are several ways to see the names and values of system variables: To see the values that a server will use based on its compiled-in defaults and any option files that it reads, use this command: mysqld --verbose --helpTo see the values that a server will use based on its compiled-in defaults, ignoring the settings in any option files, use this command: mysqld --no-defaults --verbose --helpTo see the current values used by a running server, use the SHOW VARIABLES statement. This section provides a description of each system variable. Variables with no version indicated are present in all MySQL 5.4 releases. For historical information concerning their implementation, please see http://www.mysql.com/products/enterprise//5.0/en/, and http://www.mysql.com/products/enterprise//4.1/en/. The following table lists all available system variables: Table 5.2. System Variable SummaryName Cmd-Line Option file System Var Var Scope Dynamic
auto_increment_increment Yes Yes Yes Both Yes
auto_increment_offset Yes Yes Yes Both Yes
autocommit Yes Session Yes
automatic_sp_privileges Yes Global Yes
back_log Yes Yes Yes Global No
basedir Yes Yes Yes Global No
big-tables Yes Yes Yes
- Variable: big_tables Yes Session Yes
binlog_cache_size Yes Yes Yes Global Yes
binlog-format Yes Yes Yes
- Variable: binlog_format Yes Both Yes
bulk_insert_buffer_size Yes Yes Yes Both Yes
character_set_client Yes Both Yes
character_set_connection Yes Both Yes
character_set_database[a] Yes Both Yes
character-set-filesystem Yes Yes Yes
- Variable: character_set_filesystem Yes Both Yes
character_set_results Yes Both Yes
character-set-server Yes Yes Yes
- Variable: character_set_server Yes Both Yes
character_set_system Yes Global No
character-sets-dir Yes Yes No
- Variable: character_sets_dir Yes Global No
collation_connection Yes Both Yes
建议还是先看一下MYSQL的文档，否则这个问题会需要很多篇幅来介绍。
简单一点，有些参数可以在启动命令行参数设置，可以在参数文件my.cnf ，可以在MYSQL中动态用SET命令改变，但具体到每一个参数则未必相同。
http://blog.csdn.net/jiaweiqq123/article/details/6970029