Tom:

I recently read your archived article and learned a lot.
however i have some question regarding "set size of rollback
segments'

<Quote>
To find out the size and number of rollback segments needed
to handle normal processing on the database you need to do
some testing. A good test is to start with small rollback
segments and allow your application to force them to extend.
Here are the steps to run such a test:

o Create a rollback segment tablespace.

o Select a number of rollback segments to test and create
them in the tablespace.

o Create the rollback segments so that all extents are the
same size. Choose an extent size that you suspect will
need between 10 to 30 extents when the segments grow to
full size.

o Each rollback segments should start with two extents
before the test is run. This is the minimum number of
extents any rollback segment can have.

o Only the rollback segments that you are testing and the
SYSTEM rollback segment should be online.
Run transactions and load typical of the application.

o Watch for rollback segment contention.

o Watch for the maximum size a rollback extends to.

The maximum size any one of the rollback segments reaches
during the test is the size you want to use when
configuring. This size we will call the "minimum coverage
size". If you see contention, adjust the number of segments
and rerun the test. Also, if the largest size requires
fewer than 10 extents, or more than 30, it is a good idea to
lower or raise the extent size, respectively, and rerun the
test. Otherwise, space may be getting wasted during the
test and this would throw the number off.

At the end of this test, you will have some good base
estimates for the size and number of rollback segments
needed for normal processing. However, handling large
transactions has not been discussed yet. Calculating the
segment size needed for these types of transactions as well
as how to meet the requests for the calculated space will be
addressed.

For sizing rollback segment extents, it is strongly
recommended that each extent be of the same size. The minimum
and maximum number of extents for an individual segment should
be around twenty for best performance.
</quote>



My question is during the testing , do i need to limit
user transaction? since we only use system rollback segments
and testing rollback segments , and if we have a lot of
user transactions, i guess testing rollback will continue
grow without limit.

( such as if we have 6 testing rollback segments and our setting
for transactions_per_rollback_segment is 5, then we should limit
user transactions to 30 or something like that.)
Regards,