Rules are created using the same screen seen in Figure 6.2, “MySQL Enterprise Dashboard: Editing Rules”. To begin creating a rule from scratch, click the create rule button. However, the simplest way to create a new rule is to copy an existing one. Unlike editing an existing rule, when you copy a rule, every element of that rule is editable.

You can change the rule name, the advisor group that a rule belongs to and you can set your own version number. In Figure 6.2, “MySQL Enterprise Dashboard: Editing Rules”, you have already seen how the threshold and frequency of a rule may be altered.

Most importantly you can alter a rule's expression. Expressions are the core of a MySQL Enterprise Advisor and are used to define the scenario being monitored. An expression can be as simple as a single server parameter or can be quite complex, combining multiple parameters with various mathematical operations.

An expression has two main characteristics:

If an expression evaluates to true for a specific server, an alarm is raised, indicating that a best practice is not being followed. If an expression evaluates to false no alarm is raised because the best practice is indeed being followed.

For example, if having binary logging enabled is considered a best practice for a production server (which we believe it is), then this best practice is being violated if log_bin is OFF. Consequently, the expression for the “Binary Logging Not Enabled” rule is “%log_bin% == OFF”. If this evaluates to 1, an alarm is raised because the best practice is not being followed.

An expression is made up of one or more variables and zero or more mathematical operators. The MySQL Enterprise Monitor uses the MySQL database server's expression parser and evaluator For a complete list of operators and functions see Functions and Operators. For a complete list of the built-in variables used when creating rules see Server Option and Variable Reference.

Creating an expression is dependent on variables defined in the Variable Assignment frame. This frame links variables used in the expression field with data gathered from the target MySQL server instance—server status variables, operating system status information, and table information. Variable names are associated with elements in the Data Item drop-down list. If you need to define more than one variable simply click the add row button. For a complete listing of the data collection items used in creating rules see Appendix F, Data Collection Items.

The remaining fields determine the information that displays in a notification email or the informational pop-up window associated with each advisor.