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

Visit the Below Website to access unlimited exam questions for all IT vendors and Get Oracle Certifications for FREE
http://www.free-online-exams.com

Sometimes Parallel Rollback of Large Transaction may become very slow. After killing a large running transaction (either by killing the shadow process or aborting the database) then database seems to hang, or SMON and parallel query servers taking all the available CPU. 

In fast-start parallel rollback, the background process SMON acts as a coordinator and rolls back a set of transactions in parallel using multiple server processes.

Fast start parallel rollback is mainly useful when a system has transactions that run a long time before a commit, especially parallel Inserts, Updates, Deletes operations. When SMON discovers that the amount of recovery work is above a certain threshold, it automatically begins parallel rollback by dispersing the work among several parallel processes.

There are cases where parallel transaction recovery is not as fast as serial transaction recovery, because the PQ slaves are interfering with each other. It looks like the changes made by this transaction cannot be recovered in parallel without causing a performance problem. The parallel rollback slave processes are most likely contending for the same resource, which results in even worse rollback performance compared to a serial rollback. 



Solution
======
To disable the parallel rollback by setting the following parameter
fast_start_parallel_rollback = false

Refer to Oracle Note ID 464246.1

Get Oracle Certifications for all Exams
Free Online Exams.com