Using System Variables •Modifying an option file requires direct access to that file, which requires login access to the MySQL server host. This is not always convenient. •Modifying system variables with  SET GLOBAL  is a runtime capability that can be done from clients run locally or from remote hosts, but the changes affect only the currently running server instance. The settings are not persistent and do not carry over to subsequent server startups. To augment administrative capabilities for server configuration beyond what is achievable by editing option files or using  SET GLOBAL , MySQL provides variants of  SET  syntax that persist system variable settings to a file named  mysqld-auto.cnf  file in the data directory. Examples: SET PERSIST max_connections = 1000; SET @@PERSIST.max_connections = 1000; SET PERSIST_ONLY back_log = 100; SET @@PERSIST_ONLY.back_log = 100; MySQL also provides a  RESET PERSIST  statement for removing persisted system variables from mysqld-auto.cnf . Server configuration performed by persisting system variables has these characteristics: •Persisted settings are made at runtime. •Persisted settings can be made from local clients or clients who connect from a remote host. This provides the convenience of remotely configuring multiple MySQL servers from a central client host. •Persisted settings are permanent. They apply across server restarts. •An administrator with sufficient privileges can reconfigure a server by persisting system variables, then cause the server to use the changed settings immediately by executing a  RESTART  statement. •To persist system variables, you need not have login access to the MySQL server host or file system access to option files. Ability to persist settings is controlled using the MySQL privilege system. See Section 5.1.9.1, “System Variable Privileges” . •Persisted settings provide immediate feedback about errors. An error in a manually entered setting might not be discovered until much later.  SET  statements that persist system variables avoid the possibility of malformed settings because settings with syntax errors do not succeed and do not change server configuration. Syntax for Persisting System Variables These  SET  syntax options are available for persisting system variables: •To persist a global system variable to the  mysqld-auto.cnf  option file in the data directory, precede the variable name by the  PERSIST  keyword or the  @@PERSIST.  qualifier: SET PERSIST max_connections = 1000; SET @@PERSIST.max_connections = 1000; 939 SET PERSIST_ONLY back_log = 1000; •To persist a global system variable to the  mysqld-auto.cnf  file without setting the global variable runtime value, precede the variable name by the  PERSIST_ONLY  keyword or the  @@PERSIST_ONLY. qualifier: Like  SET GLOBAL ,  SET PERSIST  sets the global variable runtime value, but also writes the variable setting to the  mysqld-auto.cnf  file (replacing any existing variable setting if there is one).