Marry,

Sorry, while I was writing my previous post you informed us you've found out the reason for your RB growth. So ju can simply ignore what I have written.

Now to your second question:

The first column in v$rollstat is USN which stands for Undo Segment Number, in other words rollback segment number. You can get the name of the particular segment number by looking at DBA_ROLLBACK_SEGS (columns SEGMENT_NAME and SEGMENT_ID).

HTH,