Question on REDO & SCN

I am presently reading Expert one-on-one oracle, but have a few questions:

1. After a DML statement all the required redo is generated. But if i commit there is a small amount of redo generated. What is this redo ? (i think that this redo is is generated after the undo is updated with the SCN on COMMIT)
2. delay block cleanout happens by getting the status of the transaction from the UNDO. In case the undo is overwritten, then it gives an error. My questions is why does it not take the SCN for that transaction from the redo (if not avaible in undo) and do block cleanout?

Thanks

Pradeep Received on Thu Nov 24 2005 - 08:52:45 CST