Explanation:
This view displays a histogram of statistical data to show how well the system is working. Each row in the view keeps statistics collected in the instance for a 10-minute interval.You can use this view to estimate the amount of undo space required for the current workload. The database uses this view to tune undo usage in the system. This view is available in both SMU (system managed undo) mode and RBU (rollback segment undo) mode.
Incorrect Answers:
2: This dynamic view contains rollback segment statistics.
3: This dynamic view lists the active transactions in the system
4: The DBA_UNDO_EXTENTS data dictionary view is used to show information about extents in the UNDO segments.
5: The DBA_ROLLBACK_SEGS data dictionary view contains information about rollback segments.
Reference:
OCP Oracle9i Database: New Features for Administrators, Daniel Benjamin, p. 160-164
Chapter 3: Manageability Enhancements
Oracle 9i New Features, Robert Freeman, p. 24-25
Chapter 1: Oracle9i Database Administration and Management Features

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