The undo tablespace is definitely required for full recovery of the database. First your restore then you roll forward then you rollback at the end to create a consistent image.
What kind of rman backup is being used? Backup pieces or copy, full or incremental, etc ... I expect at some point the full undo tablespace was used hence the full tablespace data files get backed up.
From: oracle-l-bounce_at_freelists.org On Behalf Of MacGregor, Ian A.
Sent: Tuesday, December 15, 2009 12:08 PM
Cc: wellmetus_at_gmail.com; email@example.com
Subject: Re: backup UNDO Tablespace (dba_undo_extents)
The undo tablespace is required for database recovery
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On Dec 15, 2009, at 8:51 AM, "Guillermo Alan Bort" > wrote:
Short answer... don't take a backup of the undo tablespace... it's not required for database recovery.
On Tue, Dec 15, 2009 at 1:20 PM, Roger Xu <wellmetus_at_gmail.com> wrote:
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;
Any explanation? How do I keep the backup of undo small?