How do rollback segments work

When a rollback segment changes current extents, does it immediately wipe out all undo information in that extent, or does it only overwrite old undo information in that extent as it needs to?

Another question: Lets assume a RBS has 2 extents and e1 is the current extent. If transactions come into the RBS and commit or rollback before e1 fills up, will e1 always remain the current extent? Or will it eventually move to e2, even though there's never enough active undo data to fill e1?

I ask because I'm trying to address the age old "ora-1555 snapshot too old problem". I figured that if it wipes the entire extent up front, and if the current extent only changes when it absolutely needs to, I might be able to reduce the likelyhood of ora-1555 by decreasing the extent size.
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Chuck Hamilton
chuckh_at_dvol.com

If at first you don't succeed, sky diving isn't for you. Received on Fri Aug 28 1998 - 10:36:59 CDT