Short answer... don't take a backup of the undo tablespace... it's not required for database recovery. Alan.- On Tue, Dec 15, 2009 at 1:20 PM, Roger Xu <wellmetus@xxxxxxxxx> wrote: > Good morning, > > Background: Windows 2003 / Oracle 10g with auto undo (8K block size) > > We have only one datafile (20 GB) in the undo tablespace. > When I ran RMAN backup of this datafile, it created a 20GB backupset file. > > I query dba_undo_extents and it shows less than 80 MB used. > > SQL> select sum(blocks) from dba_undo_extents; > SUM(BLOCKS) > ----------- > 9824 > > Any explanation? How do I keep the backup of undo small? > > Thanks, > Roger Xu > > >