Oracle Database Discussions

Hi ,

i want to monitor the used / free space in my undo tablespaces (RAC) and use the following query to find the used space:

SELECT
tablespace_name,
SUM(bytes) bytes
FROM DBA_UNDO_EXTENTS
WHERE status = 'ACTIVE'
GROUP BY tablespace_name;

then i compare it with the total size of this tablespace...

but this shows a big difference to the output of Enterprise Manager ( Grid Control )..

is it the wrong approach ?

thanks in advance