More processes mean better performance. This is the coda behind Fast-Start parallel rollback.
Oracle background processes coordinate and roll back a set of transactions by using multiple server processes.
Whenever a large number of transactions (like
DELETE statements) have not been committed,
Fast-Start parallel rollback becomes very important.
When the System Monitor process realizes that a large number of transactions must be rolled back, and it is faster to roll back in parallel than serially,
the System Monitor starts multiple server processes, rolling back the transactions.
Each server process handles one transaction and the performance is improved.
Fast-start parallel rollback has a special feature called intra-transaction recovery, whereby a single transaction is divided among several processes. This happens when one transaction is large, meaning it takes longer for one process to roll this transaction back than for the other processes to roll back their transactions. Oracle automatically begins intra-transaction recovery by dispersing the large transaction among the processes.
Setting the parameter
to one of the following three values controls the number of processes involved in
FALSE: Turns off Fast-Start parallel rollback
LOW: Specifies that the number of recovery servers may not exceed twice the value of the
HIGH: Specifies that the number of recovery servers may not exceed four times the value of the
An instance is recovered using RMAN, by issuing the
This is called Fast-Start-parallel rollback, and you must define the degree of parallelism while issuing the command.