DBA_UNDO_EXTENTS describes the extents comprising the segments in all undo tablespaces in the database.
The status of the undo space distribution reported by DBA_UNDO_EXTENTS is correct for the undo tablespace that is active on the instance on which DBA_UNDO_EXTENTS is queried. However, due to the use of in-memory information that is different on each instance, there can be a discrepancy in the status of the undo space distribution of undo tablespaces active on other instances when queried from one instance. This does not affect undo functionality and is only a reporting discrepancy for other instances' undo tablespace space distribution status. As a best practice, query the space distribution for an undo tablespace from the instance on which it is active.
Owner of the undo tablespace
Name of the undo segment
Name of the undo tablespace
ID of the extent
File identifier number of the file containing the extent
Start block number of the extent
Size of the extent (in bytes)
Size of the extent (in blocks)
Relative number of the file containing the segment header
Commit time of the undo in the extent expressed as Julian time. This column is deprecated, but retained for backward compatibility reasons.
Commit time of the undo in the extent expressed as Wallclock time.This column is deprecated, but retained for backward compatibility reasons.