Well, today, I stumbled across 10 active database sessions, all from the same user, all running an anonymous PL/SQL block issued within SQL Commands on apex.oracle.com. All 10 sessions had been running for hundreds of seconds and all 10 were in the APEX_LOW resource consumer group. By using the built-in-to-APEX Utilities -> Database Monitor -> Sessions reports, I was able to determine exactly what was executing in these sessions.
What's wrong with this user's code?
WHILE (i<5) LOOP
IF( mod(i,2)=0) THEN
I am NOT suggesting you run this on apex.oracle.com nor your own instance of Application Express.