Thanks Slaine.
In fact I have 4 rollback segments considering the amount of concurrent tansanction but I'd like to understand if the way I used to calculate the size is correct.I can not use th SET TRANSACTION...USE ROLLBACK SEGMENT because the operations are executed by external tools and I can't manage those transactions.I can only try to configure in the best way my rollback segments.
If You have any other idea or if you can aswer the way i used to calculate my rollback segments tell me.
Thaks
Bye