Re: Rollback segments question (shrink)

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.

>