V$STANDBY_EVENT_HISTOGRAM displays the histogram of apply lag on the physical standby. Each distinct value of apply lag has its own bucket and the count in the corresponding bucket represents the number of occurrences so far. The physical standby samples the apply lag every second and increments the corresponding bucket in the histogram.

Column Datatype Description
NAME VARCHAR2(64) Name of the event (currently APPLY LAG is the only valid value)
TIME NUMBER Time duration that the bucket represents
UNIT VARCHAR2(16) Time unit (seconds, minutes, hours, or days)
COUNT NUMBER Each row is a histogram bucket for apply lag. COUNT is the number of occurrences the apply lag falls into the histogram bucket.
LAST_TIME_UPDATED VARCHAR2(20) Last time the bucket was updated by an event falling into that time duration