"Wait for a undo record" and "Wait for stopper event to be increased"

Hello everyone,

I´ve received a lot of events the "Wait for a undo record" and "Wait for stopper event to be increased" in my Oracle Database 11.2.0.3

As follow the Note ID 464246.1, those events happen because my fast_start_parallel_rollback is set to 'LOW', and therefore the background process SMON acts as a coordinator and rolls back a set of transactions in parallel using multiple server processes.

The solution to this issue is set the parameter to false, but I don´t want to change the parameter, because first of all, I need to understand and I need how to find out how much rollback a session has to do and which transactions of rollback were running.