Re: backup UNDO Tablespace (dba_undo_extents)

From: Yong Huang <>
Date: Wed, 16 Dec 2009 07:43:46 -0800 (PST)
Message-ID: <>

> I think RMAN will back up all blocks that have ever been part of
> any segment.


That's the case up to 10gR1. Beginning with 10gR2, unused blocks in LMT are ignored, unused in the sense that the segment is dropped or truncated. See "Unused Block Compression" at

> Oracle 10g
> 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.


Tell us the exact version of Oracle. Could it be 10gR1? Your total undo tablespace is 20 GB. Is total free space (sum(bytes) from dba_free_space) for undo more than 19 GB? And I suppose you're not doing datafile image copy.

Yong Huang       

Received on Wed Dec 16 2009 - 09:43:46 CST

Original text of this message