Re: RBS problem

tigsar_at_my-deja.com wrote:

> Yes, tablespace in autoextend mode
> if I set autoextend off, will I have any problem ?
>
> In article <396E10CB.F50B2753_at_fmr.com>,
> Karen <karen.abgarian_at_fmr.com> wrote:
> > It would be interesting to hear feedback from the original poster.
> >
> > We can close the subject if the tablespace's datafiles are in
> > autoextend mode.
> >
> > Are they?
> >
> > Brian McKerr wrote:
> >
> > > Ethan Post wrote:
> > >
> > > > Rollback segments are suppose to shrink and grow. I suggest
> > > > reading the concepts manual and getting up to date on exactly
> > > > how rollback segments work.
> > > >
> > > > http://hojohn.photo.net/ora81/DOC/server.815/a67781/c02block.htm#
> > > > 8401
> > > >
> > > > -Ethan
> > > > ******
> > > > http://www.freetechnicaltraining.com/article_10.htm
> > > > http://www.gnumetrics.com
> > > >
> > > > -----------------------------------------------------------
> > > >
> > > > Got questions? Get answers over the phone at Keen.com.
> > > > Up to 100 minutes free!
> > > > http://www.keen.com
> > >
> > > Sounds like at least one of the datafiles that belongs to your RBS
> > > tablespace is AUTOEXTENDING !
> > >
> > > Cheers,
> >
> >
>
> Sent via Deja.com http://www.deja.com/
> Before you buy.

things that you may want to consider;

How many rollback segements do you have ? I would suspect that you may have to few rollback segments (default of 4 maybe) and when there are 2 or more largish transactions using the same rollback segment it extends to a much greater size and much quicker, maybe this is what is causing your tablespace to extend ? A transactions CAN share rollback segments with other transactions but a single transaction CANNOT use 2 different rollback segments during its execution. So, if you have multiple large-ish transactions executing at the same time then you should probably have multiple rollbacks segments too, this can help avoid 2 or more transactions using the same segment at the same time at it uses a round-robin algorithm (I seem to remember !) to choose which segment to use for each individiual transaction.

I would check the HWMSIZE field value in v$rollstat - this shows the how big each ROLLBACK SEGMENT has grown to and it can be used as a rough estimate on your transaction sizes. You can deduce that if one segment is significantly larger than the rest that it was probably caused by something similar to the above scenario, or you run a large batch job and it has coincidentally used the same rollback segment every time it has run (which could be once !!!!).

Rollback segments dont shrink unless you set an optimal value OR you drop and recreate them (in which case they obviously shrink !).

Be careful when using optimal on an OLTP instance, it can cause performance problems when you set it too low. Use the HWMSIZE in v$rollstat and set optimal with this value in mind , that is if you plan on using optimal.

Make sense ?

Cheers,

BM. Received on Sat Jul 15 2000 - 00:00:00 CDT