RBS dont shrink

[mattias]

Any ideas why rbs dont shrink ? I have optimal set. I can shrink it manually. Heard that it wont shrink until a new tx comes along and uses it but that seems strange.

[mattias]

Well....I was too fast to post this question . Sorry, I found more information that told me how this works now. But If any of you have interesting info your welcome to post it anyway.

[julian]

Here you are some info on the subject thanks to Metalink:

"The process of shrinking back to OPTIMAL is not instantaneous. When a
transaction that has expanded the segment beyond the set value has ended, the
rollback segment does not `snap' back to the optimal size. This could have
severe performance implications and cause considerable problems with
read-consistency. The process of deallocating extents is performed during
transactions after the one which caused the segment to extend.When the head
moves from one extent to the next during a transaction, the segment size is
checked. If the segment size is currently above the optimal, the RDBMS
determines if an extent should be deallocated. An extent will only be
deallocated if there are no active transactions in the next two extents (Why
the next two extents? If only the next extent is checked for availability,
Oracle might deallocate it then try to continue with the current transaction
only to find that the following extent is used. At that point, Oracle must
reallocate an extent.). If necessary, the RDBMS will deallocate multiple
extents in a single transaction (one each time the head crosses into a new
extent) until the segment has shrunk back to its optimal size. Since extents
are deallocated by the current transaction(s), the circular nature of rollback
segments guarantees that these are the oldest inactive extents (and the least
likely to be used for read consistency). "