Re: How many rollback segments can a transaction use?

michael ngong wrote:

> Oracle8(TM) Server Concepts "
>
> When a transaction runs out of space in the current extent and needs
> to continue writing, Oracle finds an available extent of the same
> rollback segment
> "
> This I intepret to mean if two transactions are running two rollback
> segments are to be used (What my question is about)If there is another
> explanation different from the fact that transaction could start and
> stop within this interval that should help ....
>
> My version/OS Oracle 8i Hp Unix 9000.
> When I run a query for the number of transactions I get 2
> select current_utilizations from v$resource_limit where
> name='transactions'
>
> RESOURCE_NAME CURRENT_UTILIZATION
> ------------------------------ -------------------
> transactions 2
>
> When I find the change in writes after a period of say 10 minutes I
> expect may be two rollback segments to change since two transactions
> are active.From my understanding of the DOCS these two transactions
> should use two rollback segments.
> but five of my rollback segments indicate an increase in the amount of
> writes
> time:3:50a
>
> select n.name,writes from v$rollstat r,v$rollname n where n.usn=r.usn;
> SYSTEM 2580
> RBS1 101758434
> RBS2 241709876
> RBS3 31058582
> RBS4 37506164
> RBSBIG 62053292
> Time 4:10a
> select n.name,writes from v$rollstat r,v$rollname n where n.usn=r.usn;
> SYSTEM 2580
> RBS1 112648128
> RBS2 241712898
> RBS3 111247476
> RBS4 37512038
> RBSBIG 62058182
>
> I should be missing something and will greatly appreciate your insight
>
> Michael Tubuo Ngong

There is an init.ora parameter that controls the number of transactions per rollback segment. The deault is usually 4 or 5.

A transaction can use one, and only one, rollback segment.

If you have 9i drop rollback and go to undo.

--
Daniel Morgan
http://www.outreach.washington.edu/extinfo/certprog/oad/oad_crs.asp
damorgan_at_x.washington.edu
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