The rollback is very slow, how do I speed it up?

 This is a very common problem, we kill an update/merge and is taking forever to rollback.

 There are 2 solutions for this:

1) Kill the spid oracle shadow process and set the parameter below:

SQL> alter system set fast_start_parallel_rollback=HIGH;

2) Bounce the DB and set the same parameter as above.

SQL> alter system set fast_start_parallel_rollback=HIGH;

 The only issue now, to monitor the rollback, we'll need a different query:

SQL>   SELECT usn, state, undoblockstotal "Total",undoblocksdone "Done",undoblockstotal-undoblocksdone "ToDo", DECODE(cputime,0,'unknown',SYSDATE+(((undoblockstotal-undoblocksdone) / (undoblocksdone / cputime)) / 86400)) "Finish at" FROM v$fast_start_transactions;