Re: PARALLEL_MAX_SERVERS value
- From: Greg Rahn <greg@xxxxxxxxxxxxxxxxxx>
- To: Christian.Antognini@xxxxxxxxxxxx
- Date: Wed, 26 Oct 2011 09:19:59 -0700
To add a bit more, using PARALLEL_MAX_SERVERS to control (resource
manage) is probably not the right way. That is exactly why database
resource manager (DBRM) has knobs to control things like max DOP and
active sessions. Use the right tool for the job.
On Wed, Oct 26, 2011 at 12:09 AM, Christian Antognini
<Christian.Antognini@xxxxxxxxxxxx> wrote:
> Hi
>
>> But CPUx10 es definitely too many because IMHO a CPU, either thread or core
>> should not handle more than 4 requests, 10 is a lot!
>
> FWIW at page 495 of TOP I wrote "...a value of 8-10 times the number of cores
> (in other words, the value of the initialization parameter cpu_count) is a
> good starting point".
>
> I generally do not see a problem with such "high" values because:
> - Slaves might be allocated to a specific execution but do nothing.
> - Parallel processing is, generally, I/O bound. Especially with current CPUs
> you hit the I/O limit way before the system is CPU bound.
> - Setting parallel_min_percent to values higher than the default (0) is in
> many cases not an option.
>
> IMO "low" values are only good when you control what's going on and,
> therefore, you can avoid that there are too many downgrades.
>
> In summary, I generally prefer to have a system where too many slaves are
> allocated as the opposite. It goes without saying that there are exceptions!
--
Regards,
Greg Rahn
http://structureddata.org
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