Transaction recovery: lock conflict caught and ignored

Symptoms:
I have  many  "Transaction recovery: lock conflict caught and ignored"  in alert.log
and Also I have  ORA-01555  errors

Cause
One  long transactions  interreputed  and  try  to recover so  UNDORBS is full

Solution

• I have  checked  according  to   Oracle rollback - undo monitoring tips
• Then I have  added  datafile to UNDORBS in order  not  to have  the errors  until transaction recovery
• I have  checked   but  the transaction recovery  is  very  slow
  
  select
  CPUTIME,cputime/3600,UNDOBLOCKSDONE ,UNDOBLOCKSTOTAL ,
  CPUTIME/UNDOBLOCKSDONE*UNDOBLOCKSTOTAL/60/60
  from GV$FAST_START_TRANSACTIONS;
• I have  set   FAST_START_PARALLEL_ROLLBACK  parameter  in order to speed  the  recovery 
  
  ALTER SYSTEM SET FAST_START_PARALLEL_ROLLBACK = HIGH;
• After  recovery  everything is  fine