Re: parallel hint

From: Greg Rahn <greg_at_structureddata.org>
Date: Thu, 4 Mar 2010 10:18:22 -0800
Message-ID: <a9c093441003041018w457fa7e6j9a96b3645450cfad_at_mail.gmail.com>



The "default" DOP is cpu_count * parallel_threads_per_cpu, however if the execution plan has both producer/consumer slave sets, it will use 2 * DOP parallel execution servers.

For example, with cpu_count=12 and parallel_threads_per_cpu=2, the default DOP would be 12 * 2 = 24, however the query could use 48 parallel execution servers depending on the execution plan.

On Thu, Mar 4, 2010 at 8:13 AM, girlgeek <girlgeek_at_live.com> wrote:
> Ric,
> Thank you for the explanation.  I had always wondered about something that I
> saw at a prior shop.  Someone had used a  parallel hint without degree and
> managed to get 57 parallel processes running, (mostly fighting) on a 12 cpu
> box.   If the table was defined as parallel without a degree, the
> documentation says that Oracle defines that the degree of parallelism to use
> is the number of cpu times the value in the init parameter
> parallel_threads_per_cpu. I didn't check at the time, but I assume that they
> must have set the init parameter parallel_threads_per_cpu to 4.  There are a
> few extra processes not explained by that logic, but I no longer have access
> to that particular box to research further.
>
> Thanks again,
> Claudia

-- 
Regards,
Greg Rahn
http://structureddata.org
--
http://www.freelists.org/webpage/oracle-l
Received on Thu Mar 04 2010 - 12:18:22 CST

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