What was the actual DOP for my query ? (ASH and the PX_FLAGS)

In this post i will show a quick way to check for the actual DOP for a past query(Only for version higher than 11.2.0.2).We will be using for that ASH and the undocumented column PX_FLAGS (Randolf Geist already talked about that and used it in his awesome utility XPLAN_ASH http://oracle-randolf.blogspot.com/2014/03/new-version-of-xplanash-utility.html)

Let’s begin with a simple query using one DFO (Like you may know it’s not the query that run in parallel. It’s the Data flow operations and a query may contain many of them)