Re: backup UNDO Tablespace (dba_undo_extents)

From: Jeremiah Wilton <>
Date: Tue, 15 Dec 2009 10:34:10 -0800
Message-Id: <>


As Mark P. pointed out, RMAN in 10g does not back up regions of datafiles that have never been used. However, it seems like at some point the whole tablespace filled with undo segments, then some segments shrunk or went away. I think RMAN will back up all blocks that have ever been part of any segment.

If you want to make the backup small again, in line with the current allocation of undo, then switch to a new undo tablespace and drop the old one. This will work until someone does a giant transaction again!

Or you could take the other advice someone gave and never back up undo tablespaces. Maybe skip SYSTEM too! (***JUST KIDDING***).


Jeremiah Wilton
Blue Gecko, Inc.

On Dec 15, 2009, at 9:17 AM, Roger Xu wrote:

> This thread is nothing to do with the reason why we need to backup
> undo. I just want to backup the undo segments which are required for
> recovery but not the entire undo datafile. (I know 11g skips
> commited before image but I am at 10g.)
> On Tue, Dec 15, 2009 at 11:07 AM, MacGregor, Ian A. <
> > wrote:
> The undo tablespace is required for database recovery
> 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 <>
>> wrote:
>> 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.
>> ...
>> Any explanation? ...

Received on Tue Dec 15 2009 - 12:34:10 CST

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