Re: Rollback segments question (shrink)

thank you so much - its clear now

Jonathan Lewis wrote:

> Correct in all points.
> The purpose of the optimal size is as follows:
> a) The smaller the volume of rollback space the better for performance
> reasons
> (though not for other reasons)
>
> b) Some transactions may occasionally use too much space, and therefore
> force the rollbacks to grow until the transaction commits.
>
> By choosing a good optimal size, any rollback that grows because of
> a 'special case' transaction will eventually shrink back to the more
> desirable
> small size.
>
> Because the actual grow and shrink has an overhead, the tricky bit is
> choosing a size of rollback segment that is as small as possible without
> resulting in so many grows and shrinks that the benefit of the small size
> is lost in the overhead of continual growing and shrinking.
>
> --
> Jonathan Lewis
> Yet another Oracle-related web site: http://www.jlcomp.demon.co.uk
>
> Practical Oracle 8i: Building Efficient Databases
>
> Publishers: Addison-Wesley
> See a first review at:
> http://www.ixora.com.au/resources/index.htm#practical_8i
> More reviews at: http://www.jlcomp.demon.co.uk/book_rev.html
>
> Naushi Hussain wrote in message <3A649080.6CD858FD_at_alliedsignal.com>...
> >can some one really make it clear to me - from what I know that if a
 transaction
> >is running and nothing is commited and it continues to go to another
 extent, the
> >previous extent will not shrink until the transaction has commited - does
 n't that
> >make sence. It cannot get rid of the data that is not commited yet. It will
> >continue to grow over other extents until it commits without shrinking and
> >destroying the before images.
> >
> >Also I dont understand the purpose of optimal size - so fine we shrink to
 the
> >optimal size if it grows above that level. But you cannot shrink the RBS if
 it is
> >fully occupied by the same transaction still running and not commited.
> >
> >please correct me if I am wrong.
> >
  Received on Thu Jan 18 2001 - 11:23:46 CST