Current Active Session on a Oracle Table
There's a feature of the Tuning Pack called Real Time SQL Monitoring. It's available in SQL Developer, OEM, or theoretically via some package calls - but you really want a GUI for this report. 



You can see each step of the plan as it executes and see what the wait events are. You'll also see right away if it's not running with the degree of parallelization that you're expecting.

Our resident database performance expert Maria Colgan has an excellent write-up on the topic here.