The Connection-Control Plugins •If  connection_control_min_connection_delay  and connection_control_max_connection_delay  are 2000 and 3000, the adjusted delays for the fourth and subsequent failed connections are 2000 milliseconds, 2000 milliseconds, and 3000 milliseconds, with all subsequent failed connections also delayed by 3000 milliseconds. You can set the  CONNECTION_CONTROL  system variables at server startup or runtime. Suppose that you want to permit four consecutive failed connection attempts before the server starts delaying its responses, with a minimum delay of 2000 milliseconds. To set the relevant variables at server startup, put these lines in the server  my.cnf  file: To set and persist the variables at runtime, use these statements: SET PERSIST  sets the value for the running MySQL instance. It also saves the value, causing it to carry over to subsequent server restarts. To change a value for the running MySQL instance without having it carry over to subsequent restarts, use the  GLOBAL  keyword rather than  PERSIST . See Section 13.7.6.1, “SET Syntax for Variable Assignment” . The  connection_control_min_connection_delay  and connection_control_max_connection_delay  system variables both have minimum and maximum values of 1000 and 2147483647. In addition, the permitted range of values of each variable also depends on the current value of the other: Thus, to make the changes required for some configurations, you might need to set the variables in a specific order. Suppose that the current minimum and maximum delays are 1000 and 2000, and that you want to set them to 3000 and 5000. You cannot first set  connection_control_min_connection_delay  to 3000 because that is greater than the current  connection_control_max_connection_delay  value of 2000. Instead, set  connection_control_max_connection_delay  to 5000, then set connection_control_min_connection_delay  to 3000. When the  CONNECTION_CONTROL  plugin is installed, it checks connection attempts and tracks whether they fail or succeed. For this purpose, a failed connection attempt is one for which the client user and host match a known MySQL account but the provided credentials are incorrect, or do not match any known account. Failed-connection counting is based on the user/host combination for each connection attempt. Determination of the applicable user name and host name takes proxying into account and occurs as follows: 1381 •If the client user proxies another user, the account for failed-connection counting is the proxying user, not the proxied user. For example, if  external_user@example.com proxies  proxy_user@example.com , connection counting uses the proxying user, • connection_control_max_connection_delay  cannot be set less than the current value of connection_control_min_connection_delay . • connection_control_min_connection_delay  cannot be set greater than the current value of connection_control_max_connection_delay . Connection Failure Assessment [mysqld] plugin-load-add=connection_control.so connection_control_failed_connections_threshold=4 connection_control_min_connection_delay=2000 SET PERSIST connection_control_failed_connections_threshold = 4; SET PERSIST connection_control_min_connection_delay = 2000;