Re: optimal size for rollback

The difference is that you are in control of when cron fires off the command to shrink the rollback segments, and if you've any sense you'll ensure that it does so at two o'clock in the morning when no-one gives a damn.

With OPTIMAL set, SMON shrinks the rollback segment whenever a transaction needs a rollback block that is across the extent boundary from which it is currently located. In other words, the shrink happens right in the middle of a transaction, when users *would* give a damn.

The chances of a 1555 are pretty small when you do the shrink yourself at a time when no users are performing selects (ie, two o'clock in the morning again).

Regards
HJR "Daud" <daud11_at_hotmail.com> wrote in message news:f0bf3cc3.0209141653.7e6d937f_at_posting.google.com...
> One last question I hope.
> What is the different between having a cron job shrinking the rollback
> and letting oracle does it automatically by setting optimal?
> If shrinking a rollback segment to its optimal size increases the
> chances of getting ora-1555, I am sure having a cron job to do it will
> have the effect.
> I am sorry if I am being a pain but I need to understand this last
> bit.
>
> Thanks everyone!
>
> rgds
> Daud
>
> "Howard J. Rogers" <howardjr2000_at_yahoo.com.au> wrote in message
 news:<3d81e650_at_dnews.tpgi.com.au>...
> > That's what dbms_job or cron is for.
> >
> > Optimal is only slightly worse as an idea than PCTINCREASE.
> >
> > Any time Oracle does anything for you automatically, there's a price to
 pay:
> > and the price is performance.
> >
> > Don't set optimal.
> >
> > Period.
> >
> > (Or full stop, depending on your longitude).
> >
> > Regards
> > HJR
> >
> >
> > "Daud" <daud11_at_hotmail.com> wrote in message
> > news:f0bf3cc3.0209130205.2cd2db2_at_posting.google.com...
> > > Hi
> > >
> > > I have been reading quite a bit about rollback segments and I kinda
> > > agree that setting optimal size is not quite a good idea. That shows
> > > that a dba has not done his job to find out what the correct size of
> > > the rollback segment should be.
> > > This is what I am thinking of doing and let me know if it does not
> > > make sense.
> > >
> > > initial 1M
> > > next 1M
> > > minextents 6
> > > optimal 6M
> > >
> > > The reason I want to set optimal is because occasionally I have some
> > > big jobs that cause a rollback segment to grow. However, I do not want
> > > to have to manually go in and re-set its size once the jobs are done.
> > > So, I thought setting optimal will take care of it. What do you
> > > experts think?
> > >
> > > rgds
> > > Daud
Received on Sat Sep 14 2002 - 20:48:49 CDT