Rollback Segment Usage 100%

Hi,
From the Enterprise Manager I notoced that the usage of my rollback segment is 100%.

Does this mean that I have to increase the rollback segment size ??

Thanks
Anurag

Check for rbs contention first.

Hi,

Set OPTIMAL value. This will shrink the rbs after use.

Check for header waits as a % of total gets. If it is more than 1% you need more rollback segments.

Baliga

Hi

If rollback contention is there, add some more rollback segment.

Set the optsize for all the rollback segment.

HTH

Hi,
I see that there is no contention for the rollback segments.But I must tell you that there are 2 rollback segments having extent sizes of 56K each and having 348 and 330 extents respectively.

I think such a high number of extents will have an impact on performance.

What should I do do fix this and also how do I determine the optimal size of the rollback segments.

I know that you have to set a low optimal value for small transactions and high for high transactions. But shouldnt I increase the rollback segment size and set the optimal to the current usage as thats the maximum it has been used.

Please suggest.

Thanks
Anurag

Set optimal value to avg(hwmsize). Set the initial=next for the ts at half the optimal value. Extent allocation for rbs is CPU intensive, small extent size will affect performance/response time.

Hi,
check your transaction size. And assign 4 or 5 transacions per rollback segment. Say, your transaction is 50K. For 4 transactions, you need to assign an initial of 200k, make next also 200k and normally optimal is set to twice the initial.
HTH
manjunath

Hi,
How Do I calculate my transaction size and high water mark for the rollback segments. I am using Enterprise manager version 2.2 an it shows me the Used % and not the high water mark as it used to show in the previous versions.

Thanks
Anurag

Do a select hwmsize from v$rollstat

Thanks everybody,

Is there any specific reason for setting the optimal size at avg(hwmsize) . My optimal value comes out to be 20 MB. This means that my initial and next should be 10 MB each as opposed to the initial=next=56KB.

what is the best approach to do this as it is not allowed to change the initial extent once it is set. Should I create 2 more rollback segments with the above values and bring them online and finally drop the older ones.

Please suggest.

Thanks
Anurag