Select Fetching from UNDO

 we see a performance issue and Application team provided session id , we tried to figure out the detail and understand that session was executing one select statement , going further we see that most of the reads activity happening on UNDO tablespace for select statement , want to understand is fetching all records from UNDO is normal behavior or i should look for any rollback too or on which aspect such situation get raised .

     File ID % Activity Event                             % Event


--------------- ---------- ------------------------------ ----------

 Tablespace

           4237 5.30 db file sequential read 3.31  UNDOTBS2

                           gc cr disk read                      1.49


           4238       4.97 db file sequential read              2.90

                           gc cr disk read                      1.74


           4258       4.06 db file sequential read              2.24

                           gc cr disk read                      1.66


           4239       3.73 db file sequential read              2.24