Many rows in DBA_UNDO_EXTENTS

Question

Hi,
in my DBA_UNDO_EXTENTS I have many and many rows with status = UNEXPIRED
I'm reading these link:
http://download.oracle.com/docs/cd/B19306_01/server.102/b14231/undo.htm
and Oracle® Database 2 Day DBA but i don't know how i can delete these row.
If I want introduce the Retention period i can set the RETENTION GUARANTEE to the UNDO TBS, right?
Thanks a lot, as usual
Lain

Answer 1

Hello,
You can reduce the datafiles of the Undo Tablespaces as any kind of datafiles
but, you cannot go below the HWM.
Please, find enclosed a query to get the HWM position of every datafile (in Mo)
of the Undo Tablespace:
col file_name for A60
select B.file_name, (A.block_id + A.blocks)*{color:red}8{color}/1024 "Mo"
from dba_undo_extents A, dba_data_files B
where A.file_id = B.file_id
and A.block_id = (select max(C.block_id)
from dba_undo_extents C
where C.file_id = A.file_id
order by A.file_id
NB: In red the block size of your Database in Ko (here 8Ko).
You get a result like that:
FILE_NAME                                                            Mo
E:\ORACLE\ORADATA\PRD\LOG\UNDOTBS01.DBF                      30.0703125
E:\ORACLE\ORADATA\PRD\LOG\UNDOTBS02.DBF                      19.0703125
E:\ORACLE\ORADATA\PRD\LOG\UNDOTBS03.DBF                      40.0703125So, in this example, you cannot resize the first datafile below ~ 31 Mo.
Hope this help.
Best regards,
Jean-Valentin
Edited by: Lubiez Jean-Valentin on Jan 25, 2010 8:33 PM