In article <937486451.8078.1.nnrp-13.9e984b29_at_news.demon.co.uk>,
"Jonathan Lewis" <jonathan_at_jlcomp.demon.co.uk> wrote:
> It dates back to a whitepaper written for
> Oracle 5 (though is still pretty relevant).
>
> When a transaction cross an extent boundary
> no other transaction can begin in that extent.
>
> Therefore in a 2-extent rbs, a single well
> (?badly?) placed transaction could make
> the entire rollback segment unusable for
> a period.
>
> The more extents, the smaller the fraction
> of the segment that is unusable. 20 extents
> (all of the same size) denies ca. 10% of the
> RBS - the trade-off is between having
> too many extents and losing too much
> usable space in one shot.
>
> --
>
> Jonathan Lewis
> Yet another Oracle-related web site: http://www.jlcomp.demon.co.uk
>
> Laurent La Fosse wrote in message <37E0DACD.66DF24F1_at_mediaone.net>...
> >I would like to know why people recommend setting MINEXTENTS to 20
> >when creating rollback segments?
>
Jonathan, could you expand a little more on this. The manual says that
multiple transactions can share an extent but that only one transaction
writes to a rbs block within the extent. How does one transaction
needing another block which is allocated from the next extent make that
extent unusable, and for how long? If a second transaction in the
segment needs another block does it go into a different extent or does
it go into a wait state until some event?
--
Mark D. Powell -- The only advice that counts is the advice that
you follow so follow your own advice --
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Received on Fri Sep 17 1999 - 08:39:01 CDT
