Paul, The transition from RBS to UNDO is pretty easy I would suggest retaining the same size UNDO as you have RBS at the = moment, especially if you have no special (longer) retention period = requirements. The init.ora (or hopefully spfile) should be amended to remove the = following lines TRANSACTIONS_PER_ROLLBACK_SEGMENT and ROLLBACK_SEGMENTS.=20 The following parameters should be added UNDO_MANAGEMENT=3DAUTO UNDO_SUPRESS_ERROR=3DTRUE (to stop errors occuring if the commands = referring to rollback segments are used (online/offline/use etc) UNDO_TABLESPACE (multiple UNDO tablespace can be created (as normal T/S = - use LMT) but only 1 can be 'active' Drop the RBS tablespace once all sessions using it have been removed (it = can always be re-created if necessary) Experiment with the flashback_query facility, you might not need it but = it is a pretty neat thing and well worth playing with. The main view to use for monitoring information is V$UNDOSTAT where you = can determine the maximum query length and the number of undo blocks = used amongst other things. In my view this is one of the easiest of the 9i features to implement = and you should not have many problems HTH=20 John -----Original Message----- From: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx]On Behalf Of Paul Vincent Sent: Friday, September 17, 2004 9:16 AM To: oracle-l@xxxxxxxxxxxxx Subject: Undo Tablespace question Now that we've finally got some 9i databases, I'm quite keen to switch = =3D from Manual to Automatic Undo Management. It all looks pretty =3D straightforward, but I do have a couple of questions that the "How To" = =3D guides don't really address... 1. If I don't have any requirement for long-term retention of Undo data = =3D after transactions commit, so that the default retention of 900 seconds = =3D is quite sufficient, then what multiplier should I use when calculating = =3D the size of my Undo Tablespace relative to the size of the old RBS =3D tablespace? Say I currently have 500Mb RBS tablespace, then should a =3D 500Mb undo tablespace be adequate, or should I allow double (1Gb) or =3D more? 2. What monitoring practices are advisable to check the adequacy of the = =3D undo tablespace provision? Can anyone point me at any webpages with =3D articles about monitoring AUM activity, for instance? 3. Once I've switched from Manual to Auto, does the RBS tablespace then = =3D become completely superfluous? Can it be dropped? And what of the =3D "rollback_segments" initialisation parameter? Do I remove this from the = =3D parameter file, or is it best left there "just in case"? Before I go diving in, in cavalier manner, I always like to check for = =3D "gotchas"! Regards, Paul Vincent DBA University of Central England -- //www.freelists.org/webpage/oracle-l -- //www.freelists.org/webpage/oracle-l