Database system monitor data organization

The system monitor collects and stores information that you can access using interfaces to the snapshot monitor and some event monitors. The database system monitor stores information it collects in entities called monitor elements (these were previously known as data elements). Each monitor element stores information regarding one specific aspect of the state of the database system. In addition, monitor elements are identified by unique names and store a certain type of information.

The following element types are available for the system monitor to store data:

Counter: Counts the number of times an activity occurs. Counter values increase during monitoring. Most counter elements can be reset.
Gauge: Indicates the current value for an item. Gauge values can go up and down depending on database activity (for example, the number of locks held). Gauge elements can not be reset.
Watermark: Indicates the highest (maximum) or lowest (minimum) value an element has reached since monitoring was started. Watermark elements can not be reset.
Information: Provides reference-type details of your monitoring activities. This can include items such as partition names, aliases, and path details. Information elements can not be reset.
Timestamp: Indicates the date and time that an activity took place by providing the number of seconds and microseconds that have elapsed since January 1, 1970. For the snapshot monitor and event monitors, the collection of timestamp elements is controlled by the TIMESTAMP monitor switch. While this switch is on by default, you should turn it off for performance reasons if CPU utilization on the database instance approaches 100%. Timestamp elements can not be reset.
A value of 0 for the timestamp element means "not available". If you attempt to import this data, such a value will generate an out of range error (SQL0181). To avoid this error, update the value to any valid timestamp value before exporting the data.
Time: Returns the number of seconds and microseconds spent on an activity. For the snapshot monitor and event monitors, the collection of most time elements is controlled by the TIMESTAMP monitor switch. While this switch is on by default, you should turn it off for performance reasons if CPU utilization on the database instance approaches 100%. Some time elements can be reset.

Monitor elements collect data for one or more logical data groups. A logical data group is a collection of monitor elements that gather database system monitoring information for a specific scope of database activity. Monitor elements are sorted in logical data groups based on the levels of information they provide. For example, while snapshot monitoring, the Total Sort Time monitor element returns database (dbase), application (appl), and statement (stmt) information; hence, it appears in each of the logical data groups listed in parentheses.

Although many monitor elements are used by both the snapshot monitor and event monitors, they each use a distinct set of logical data groups. This is because the scopes of database activity for which you can capture a snapshot differ from those for which you can collect event data. Practically speaking, the overall set of monitor elements accessible from the snapshot monitor is different from those accessible from event monitors.