As of MySQL 5.5.3, the server provides a pluggable audit interface that enables information about server operations to be reported to interested parties. Currently, audit notification occurs for these operations (although the interface is general and the server could be modified to report others):
Write a message to the general query log (if the log is enabled)
Write a message to the error log
Send a query result to a client
Audit plugins may register with the audit interface to receive notification about server operations. When an auditable event occurs within the server, the server determines whether notification is needed. For each registered audit plugin, the server checks the event against those event classes in which the plugin is interested and passes the event to the plugin if there is a match.
This interface enables audit plugins to receive notifications only about operations in event classes they consider significant and to ignore others. The interface provides for categorization of operations into event classes and further division into event subclasses within each class.
When an audit plugin is notified of an auditable event, it receives a pointer to the current THD structure and a pointer to a structure that contains information about the event. The plugin can examine the event and perform whatever auditing actions are appropriate. For example, the plugin can see what statement produced a result set or was logged, the number of rows in a result, who the current user was for an operation, or the error code for failed operations.
For more information about audit plugins, see Section 23.2.5.2, “Writing Audit Plugins”.