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Home -> Community -> Mailing Lists -> Oracle-L -> Re: Rollback Segment Philosophy
Kevin,
"I Undo Therefore I AUM" ;)
What size and number are the rollback segments and how large is the tablespace? Is there problematic sql that is causing these problems?
Let's assume that the sql is good and it is a space-related issue. You need to allocate more space to rollback segments. (Don't you just love my keen grasp of the obvious?). Where to allocate more space is the key. Basic approach is to size your rollback segments as a mirror of your transaction. If the transactions are many and small, use many, small rollback segments. If the transactions are few and large, use few and large rollback segments. As a baseline, I have used 20 rollback segments each sized about 10 megs to start.
Contrary to popular opinion, I set OPTIMAL so that a rogue transaction or two don't have lingering impact.
In terms of operation, if you see header waits in v$rollstat, you need to add rollback segments. This means that too many transactions were trying to access the structures in the undo header at the same time.
You might want to peruse my papers on undo at www.optimaldba.com/library.html and Tim Gorman's "Cats, Dogs and ORA-1555s" at www.evdbt.com.
Regards,
Daniel Fink
Kevin Lange wrote:
> Evening;
> Is there 'accepted' philosophy on Rollback Segments and how many and how
> big they should be ?
>
> We are running an 8.1.7.4 database on Solaris 5.9. The database is a hybrid
> Transactional with some long running processes.
>
> We have always made it a point to have a limited number of rollback segments
> using a limited amount of space. But, the issue of no space no longer
> applies.
>
> Since we are starting to get rollback issues due to running out of space on
> our rollback segments we have decided to reopen our analysis of our rollback
> design.
>
> I was just wondering if any of you would mind sharing your philosophy on
> Rollbacks .
>
> Thanks
>
> Kevin
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