RE: parallel_adaptive_multi

From: Herring Dave - dherri <Dave.Herring_at_acxiom.com>
Date: Wed, 24 Jan 2007 15:11:10 -0600
Message-ID: <7ED53A68952D3B4C9540B4EFA5C76E3602BC7742@CWYMSX04.Corp.Acxiom.net>

My hope is to get more information about what the reduction factor is. I've got parallel_threads_per_cpu set so that I can count on a certain default degree. But I'd like a good idea of specifics related to when the reduction factor kicks in and what values get chosen to reduce the degree.

Dave

Dave Herring, DBA
Acxiom Corporation
3333 Finley
Downers Grove, IL 60515
wk: 630.944.4762
<mailto:dherri_at_acxiom.com>

"When I come home from work and see those little noses pressed against the windowpane, then I know I am a success" - Paul Faulkner

> -----Original Message-----
> From: K Gopalakrishnan [mailto:kaygopal_at_gmail.com]
> Sent: Wednesday, January 24, 2007 3:06 PM
> To: Herring Dave - dherri
> Cc: oracle-l_at_freelists.org
> Subject: Re: parallel_adaptive_multi_user
>
> Dave,
>
> The algorithm is quite simple. We just use the cpu_count and
> parallel_threads_per_cpu to define our upper limit. With in that upper
> limit, we just allocate the required parallel degree with in our
> limit. The reduction factor is based on the number of active users on
> the system. In earlier versions , there used to be bug which doesn't
> ignore the idle sessions and causing some issues. It is fixed in 9205
> and above and the algorithm works pretty efficient these days.
>
> > I'm reluctant to set parallel_adaptive_multi_user = TRUE without
first
> having a good idea of how Oracle chooses to reduce the default degree.
> Manuals say its based on system load and active parallel users.
Great,
> but is load solely on CPU % used or some other resource combination?
For
> active parallel users, is it based on the total of PX slaves across
the
> entire database or just on the objects involved? For both factors,
what
> reduction factor is used?
>
> It does care the objects, but it applies the reduction factor on top
> of the object's parallelism. You can use 10392 event to trace the
> execution of the parallel adaptive multiuser algorithm.
>
> --
> Best Regards,
> K Gopalakrishnan
> Co-Author: Oracle Wait Interface, Oracle Press 2004
> http://www.amazon.com/exec/obidos/tg/detail/-/007222729X/
>
> Author: Oracle Database 10g RAC Handbook, Oracle Press 2006
> http://www.amazon.com/gp/product/007146509X/

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Received on Wed Jan 24 2007 - 15:11:10 CST

RE: parallel_adaptive_multi_user