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V$EVENT_HISTOGRAM displays a histogram of the number of waits, the maximum wait, and total wait time on an event basis. The histogram has buckets of time intervals from < 1 ms, < 2 ms, < 4 ms, < 8 ms, ... < 221 ms, < 222 ms, and >= 222 ms.

The histogram will not be filled unless the TIMED_STATISTICS initialization parameter is set to true.

Column Datatype Description
EVENT# NUMBER Event number
EVENT VARCHAR2(64) Name of the Event
WAIT_TIME_MILLI NUMBER Amount of time the bucket represents (in milliseconds). If the duration = num, then this column represents waits of duration < num that are not included in any smaller bucket.
WAIT_COUNT NUMBER Number of waits of the duration belonging to the bucket of the histogram
LAST_UPDATE_TIME VARCHAR2(64) Indicates the last time the bucket was updated (the ending timestamp of the last wait falling into the bucket's duration)