The frequency and thresholds defined for a rule are default recommendations. To edit these properties choose the Create/Edit Rule link.

The following image shows the screen used to edit rules:

Figure 15.43. MySQL Enterprise Dashboard: Editing Rules

Beside the rule name is the Advisor drop-down list box, used for setting the advisor group. This list box shows existing groupings and any you may have added. The Expression textarea shows the advisor rule, Variable Assignment the data item associated with variable(s) used in the rule and Thresholds determines when to trigger each alert type.

The three levels of Thresholds are Info Alert, Warning Alert, and Critical Alert indicating increasing levels of severity. Levels can be triggered by the expression result being equal to a certain value, greater than a certain value, or less than a certain value.

The data items that variables are associated with are operating system (OS) properties such as available RAM or MySQL characteristics such as the InnoDB buffer pool. To see all available data items drop down the Data Item list box. For a listing of these data items see Data Collection Items.

In Figure 15.43, “MySQL Enterprise Dashboard: Editing Rules” the drop-down Data Item list box within the Variable Assignment frame shows the various MySQL server status or operating system specific variables that may be used in expressions. The text boxes below Thresholds define the levels at which informational, warning, or critical alerts are issued.

To lower the threshold for an informational alert, simply increase the number given in the Info Alert text box.

When a data item can apply to multiple objects, you need to specify which instance to use for that item, hence the Instance text box. In almost all cases this should be set to local. The exceptions are as follows:

An agent can only collect data from one MySQL server, so the instance entry for a variable in a rule does not need to specify which MySQL server to use; no matter how many servers are being monitored there is always a one-to-one relationship between an agent and its monitored server.

However, on one server there may be multiple occurrences of a variable. For example, there are multiple possible occurrences of table-specific variables such as Avg_row_length because there can be multiple databases and tables defined in a MySQL server. In this case, the “instance” refers to the database and table that a data item should be associated with, specified in the form databasename.tablename. So, for example, if you want to reference the Avg_row_length of the mysql database user table in an expression, select the mysql:tablestatus:Avg_row_length from the Data Item list box and specify mysql.user in the Instance text box.

On the other hand, in the case of a global server variable, there is only one possible target. For example, there can only be one instance of delay_key_write because this variable is global and applies to the server as a whole. In this case specify local in the Instance text box.

To save your changes click the save button at the bottom of the page.

You can edit a rule even if it is currently scheduled. Your changes will not be overwritten when new rules are imported using the Check for Updates link.