Donald K. Burleson
Number and Placement of
controlled by the number of data manipulation language users
(INSERT, UPDATE, and DELETE commands) and the transaction load on
the system is the number of rollback segments. The formula, as
stated before, is:
NUMBER OF DML TRANSACTIONS / NUMBER OF TRANSACTIONS PER ROLLBACK
This will yield the number of rollback segments needed. They should
be sized to handle the maximum expected data manipulation language (DML)
The placement of rollback segments is decided based upon resource
contention prevention. Put them where they won’t cause contention
with other Oracle files. Transactions are spread across all active
rollback segments. Usually, it is a good idea to locate the rollback
segments in a tablespace or tablespaces dedicated to rollback
segments. This allows the DBA to easily manage these resources.
Oracle rollback segments
The size of rollback segments is based upon three factors:
* Average number of simultaneous active DML transactions.
* Average number of bytes modified per transaction.
* Average duration of each transaction.
This is an
excerpt by Mike Ault’s book “Oracle
Administration & Management”. If you want more current Oracle tips
by Mike Ault, check out his new book “Mike
Ault’s Oracle Internals Monitoring & Tuning Scripts” or
Ault’s Oracle Scripts Download.
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