One means of limiting use of MySQL server resources is to set the global max_user_connections system variable to a nonzero value. This limits the number of simultaneous connections that can be made by any given account, but places no limits on what a client can do once connected. In addition, setting max_user_connections does not enable management of individual accounts. Both types of control are of interest to many MySQL administrators, particularly those working for Internet Service Providers.
In MySQL 5.0, you can limit use of the following server resources for individual accounts:
The number of queries that an account can issue per hour
The number of updates that an account can issue per hour
The number of times an account can connect to the server per hour
The number of simultaneous connections to the server by an account (available as of MySQL 5.0.3)