Mysql system parameter system variable state variable

1, system parameters, that is, command line options, when executing the command, followed by the parameters, the system parameters are many, it is not possible to execute the program each time, specify these parameters. These parameters are written in the configuration file (under Windows My.ini,linux is MY.CNF) and are used when executing the program--defaults-file

2, System variables, system variables are MYSQLD runtime variables, these variables correspond to the system parameters when starting mysqld. Consider the following situation: When the mysqld started, when the configuration file specified a system parameter, after starting, want to modify this parameter, what to do?

The stupid Way is: Close the mysqld, modify the configuration file, restart the mysqld. A better approach: Modify the system variables directly and adjust the variable values dynamically. It is important to note that this method does not write to the configuration file, restart the mysqld, or the old system parameters.

System parameters and system variables are not strictly one by one mappings, and some have no mapping relationships.

Some system variables cannot be modified.

The system variable has the scope concept, divides into the global and the session two kinds.

Through show variables; You can view all of the system variables, with a version of 5.5 over 300.

3, state variables, record the system status of the MySQL service.

The state variable also has the scope concept, divides into the global and the session two kinds.

Through show status; You can view all the status variables, with 5.5 versions exceeding 300.

Mysql system parameter system variable state variable