Hello Sonia

When a row is under updation the commited data is stored in the rollback segment .


well that is not true..

Before a transaction that modifies data is committed the old data is stored in the rollback segment.

For each rollback segment, Oracle maintains a transaction table--a list of all transactions that use the associated rollback segment and the rollback entries for each change performed by these transactions. Oracle uses the rollback entries in a rollback segment to perform a transaction rollback and to create read-consistent results for queries.

regards
Hrishy