Re: Sizing Rollbacks segments

alawa,

Oracle support is right, there is no predefined way to caculate a Rollback Segment. You need to know what your users are doing and make adjustments as you see fit.

Here is some info that might benefit you...It comes from "Oracle7 Server:Performance Tuning Volume One Student Guide"

SIZING ROLLBACK SEGMENTS

• Choose the INITIAL storage parameter from the list 2KB, 4KB, 8KB, 16KB, 32KB, 64KB, 128KB, 256KB, 512KB, 1MB, 2MB, 4MB and so on.

If you use sizes from this list, and then drop the extent, you can reuse all the freed space without waste.

• Use the same value for NEXT as for INITIAL.
• Make all your rollback segments the same size. If you do not, they are likely to become the same size over time anyway. The smaller ones extend as they are used by large Transactions.
• Set MINEXTENTS to 20.

This makes it unlikely that the rollback segment needs to grab another extent because the extent that it should move into is still being used by an active transaction.

• Set OPTIMAL to make sure that rollback segments do not shrink below 20 extents. You must also take into consideration the need for concurrent queries.

Regards,
Satar
Oracle DBA/UNIX System Admin
"Opinions are the result of the voices in my head only, and do not reflect my employer or Oracle Corporation."

In article <867ltqo2c3.fsf_at_bandol.concept.fr>,   alawa_at_bandol.concept.fr wrote:
>
>
> Rollback segments are supposed to hold the modifications
> that occurs on a transaction until the commit.
> So, theoricaly we sould be able to predict
> the size of the rbs needed for a simple "delete table ..".
>
> Oracle support says "No, there is no rules to calculate this
> size", wich is not satisfying.
>
> We tried a simple test with a table+index of 23Mo and a single
> rbs of 30M. The "delete table" ends with the ORA-1562 error.
>
> How much space do I need ? 2 times the amount of data, 10 times ?
>
> Thank's for any pointer.
>
> AB
> alawa_at_concept.fr
>
>

-----------== Posted via Deja News, The Discussion Network ==---------- http://www.dejanews.com/ Search, Read, Discuss, or Start Your Own Received on Wed Feb 10 1999 - 14:30:49 CST