What is the best strategy for using parallelism feature in 10gR2( IBM)

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Environment Database 10gR2 on IBM )            

• cpu_count                      =12                                                                                                                                                                      
• parallel_threads_per_cpu =2                                                                                                                                                                       
• so Degree of parallelism (DOP) = 2x12 = 24

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SQL > show parameter parallel

fast_start_parallel_rollback         string   LOW