Why is OEM SQL Monitoring showing parallel on almost every statement

Question

I'm confused here.
I'm running Oracle EE 11.2.0.2 and when I look in OEM SQL Monitoring, it shows nearly every sql statement running with a degree of parallelism of *2*.
I've checked dba_tables and the 'degree' for all tables is only 1.
I look at the actual sql statement, and there are no hints to tell it to use parallelism.
So why and how is the database using parallelism?
I do see that parallel_threads_per_cpu is set to 2, but this is default for our Solaris 10 operating system.
REF: (for 11.2)
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PARALLEL_THREADS_PER_CPU specifies the default degree of parallelism for the instance and determines the parallel adaptive and load balancing algorithms. The parameter describes the number of parallel execution processes or threads that a CPU can handle during parallel execution.
The default is platform-dependent and is adequate in most cases. You should decrease the value of this parameter if the machine appears to be overloaded when a representative parallel query is executed. You should increase the value if the system is I/O bound.
I guess the next question here is how to tell if my database is actually IO bound or not?

Answer 1

Hi John. Thanks for your reply.
NAME                                 TYPE                             VALUE
parallel_degree_policy               string                           MANUALAnd so, the more I read about PARALLEL_THREADS_PER_CPU, the more I wonder if I should increase this value.
But first, I want to understand why I'm seeing parallelism in OEM set to 2 for almost everything that runs in the database, but note, NOT ALL.
Some queries, especially those running from Crystal Reports, are not using parallelism at all.
Is it possible to set a parameter at the session level that runs parallelism, and perhaps this is being done by the application?
I'm going to try increasing my PARALLEL_THREADS_PER_CPU to 4 and see if this changes the parallelism in OEM, (but I doubt it).
I should note that my most recent AWR report shows my db_file_sequential_read in the top 5 wait events.
This would imply my index reads and table reads by ROWID are waiting for disk - possibly I/O bound.
Edited by: 974632 on Jan 28, 2013 10:25 AM