As an example, this section shows how to create a data item for monitoring the amount of free InnoDB tablespace. The format and content of the XML file that defines the data to be collected is as follows:

<?xml version="1.0" encoding="utf-8"?>
<classes>
  <class>
    <namespace>mysql</namespace>
    <classname>innodb_min_free</classname>
    <query><![CDATA[SELECT MIN(substring_index(substring_index(table_comment," ",3)," ",-1)/1024/1024)
      as Free FROM INFORMATION_SCHEMA.TABLES WHERE engine = 'InnoDB']]></query>
  </class>
</classes>

The above works in MySQL 5.1.23 and earlier. For MySQL 5.1.24 and later, the information is reported within the data_Free column, and would need to be declared as:

<?xml version="1.0" encoding="utf-8"?>
<classes>
  <class>
    <namespace>mysql</namespace>
    <classname>innodb_min_free</classname>
    <query><![CDATA[SELECT MIN(data_free/1024/1024)
      as Free FROM INFORMATION_SCHEMA.TABLES WHERE engine = 'InnoDB']]></query>
  </class>
</classes>

Save this file as:

After saving this file, you must point your mysql-monitor-agent.ini file to it. ( For the location of this file on your operating system see Section 2.3.6.1, “MySQL Enterprise Monitor Agent (mysql-monitor-agent.ini) Configuration”.) Find the [mysql-proxy] section and add the file name innodb_min_free.xml to the item-files parameter using a semi-colon as a separator. For example:

[mysql-proxy]
 ...
item-files = items-mysql-monitor.xml,innodb_min_free.xml
 ...

For this change to take effect you must restart the agent. To do this see:

Once the agent has restarted, you will find the new data item in the Data Item drop down list box on the Rule Definition page. Its fully qualified name is mysql:table:innodb_min_free.