Re: Which RBS is my Update using ?

Tanel Poder wrote:

> Hello Daniel,
>
> I think wasting diskspace isn't a good practice either.
>
> The case:
> 24x7 Mixed environment (OLTP, reporting)
> Lots of users
> Lots of small transactions
> Occasional large updates and deletes :( transactions which cannot be delayed
> Reporting -> long running queries
>
> I usually don't need huge RBS'es in my OLTP system, but still
> occasionally do have a big transaction which has to complete as soon as
> possible. For that I set big transaction to use large RBS and go! And I
> don't care if any small transactions get to it as well, or even if a
> small-transaction-owner leaves his data uncommitted and goes to a pizza
> or smth, because he's kicked out of the db (not application) in less
> than a hour. (we don't allow any regular user to make arbitrary dml
> anyway - and our application doesn't just leave user transactions
> hanging for long times)
>
> I actually think that the concept of how our application uses database
> is a bit bad from database point of view, but since databases don't run
> businesses (it works the other way), I won't try to start changing it
> just because that my RBSes don't match general theoretical
> recommendations (where real life outside the database isn't considered).
>
> So, having all same sized rollback segmnents is a good, best practice in
> general conditions, but still, I don't see what use would I get by
> resizing all of my rbs'es to a huge size. So far I'm following the
> golden rule of all engineers - If it works, don't touch it ;)
>
> Or am I missing something here?
>
> Tanel Poder
> a DBA.
>
> > One might want to do what you suggest. But then again one might also wish to
> > listen to Tom Kyte, Howard Rogers, and numerous other experts here at c.d.o.
> > who will gladly tell you this is a bad practice and to not do it.
> >
> > I'll repeat myself again ... if you need to ask the question you have your
> > rollback segments improperly sized: They should all be identical and sized to
> > handle the largest transaction on the system.
> >
> > Check the google.com archives for the numerous postings by Tom and others on
> > this subject.
> >
> > Daniel Morgan
> >

What you are missing ... is that rollback segments need to be able to expand to handle the largest transaction on the system. That is not the same as saying they need to permanently be large enough to handle the largest transaction on the system.

But no matter how you look at it ... disk is far cheaper than an ORA-01555. And for the uncounted hours people spend tweaking rollback segments (calculated in dollars per hour) they could buy all the DASD Seagate can make in a year.

Daniel Morgan Received on Wed Sep 18 2002 - 10:28:20 CDT