System monitor output: the self-describing data stream
Processing event monitor data is different, in that the event data is sent to the application at the pace database events occur. For a pipe event monitor, the application waits for event data to arrive, and then processes it when it does. For a file event monitor, the application parses event files, thus processing event records in batches.
This self-describing data stream allows you to parse through the returned data one element at a time. This opens up numerous monitoring possibilities, including looking for information regarding a particular application or a specific database state.
- The size (in bytes) of the data stored in the monitor element or logical data grouping. In the case of a logical data grouping, this is the size of all data in the logical group. For example, the database logical grouping (db) contains individual monitor elements (such as total_log_used) along with other logical data groupings, such as rollforward information (rollforward). This does not include the size taken up by the 'size', 'type', and 'element' information.
- The type of element stored in the data (for example, variable length string or signed 32 bit numeric value). An element type of header refers to a logical data grouping for an element.
- element id
- The identifier for the monitor element that was captured by the monitor. In the case of a logical data grouping, this is the identifier for the group (for example, collected, dbase, or event_db).
- The value collected by a monitor for a monitor element. In the case of a logical data grouping, the data is composed of the monitor elements belonging to it.
All timestamps in monitor elements are returned in two unsigned 4 byte monitor elements (seconds and microseconds). These represent the number of seconds since January 1, 1970 in GMT time.
The size element of strings in monitor elements represents the actual size of data for the string element. This size does not include a null terminator, as the strings are not null terminated.