Using Oracle Enterprise Manager or any number of home-grown tools a DBA might have developed, pilfered, or downloaded, you can find recent SQLs that have caused the most IO. Depending on your problem, this may be a relatively fast SQL executed thousands of times, or one dirty big SQL executed just a few times (or even just once).
Ensure that the performance problem is either currently happening, or has happened recently. The information Oracle stores on performance is only temporary, so if you wait too long it may no longer be available.
Have you found the SQL you’re looking for? If so, now you can begin to analyze the problem.
If Top SQL wasn’t any help, it’s either because there were too many SQLs to investigate, or because you didn’t get to it in time. If you’ve already ruled out SQL*Text and SQL*Trace because you cannot isolate the problem, you will have to revert to a Database Trace.