Re: Rollback Segment

> noah_at_indirect.com (Noah Monsey) writes:
> mah_at_reaper.mitre.org (Michael Huneycutt) wrote:
>
> >Phuong Quach (quach_at_ext423.artecon.com) wrote:
 DELETED
> >: When do I need to create rollback segment?
 [DELETED]
> Try and make the "initial extent" large enough so that you
> don't end up with a highly fragmented tablespace.
>
>>>>

In oracle 7, smon process does the job of defragmenting the neighboring free blocks. So, for Oracle 7, I think it is better to have all the blocks of same size. This, because many of the transactions require smaller rollback segments and a few require very large rollback segments. The few transactions requiring large rollback segments may use custom rollback segments reserved for such purpose through SET TRANSACTION USE ROLLBACK SEGMENT rbs_huge. If all the extents in segments are the same, there is little chance for of tablespace defragmentation to occur. resulting in cannot allocate extent of size nnnn error.

I do agree, that the rollback segment, if it requires more than one extent, will get fragmented space in the tablespace. But that may happen for very few transactions. With extents of same size, the space will be used efficiently.

In the book 'TUNING ORACLE' by Oracle Press, the authors favor having initial extent large enough.

Any comments?

Ganesh Puranik Received on Mon May 22 1995 - 00:00:00 CEST