RE: Parallel procesing configuration.
- From: "Mark W. Farnham" <mwf@xxxxxxxx>
- To: <jcmiranda@xxxxxxxxx>, <oracle-l@xxxxxxxxxxxxx>
- Date: Fri, 4 Dec 2009 16:06:51 -0500
Usually when someone writes OLTP, that means there are at least a few
interactive transactions where you do not want to keep a human being
waiting. Humane designers of applications suites plan so that there is
sufficient headroom of processing capability that the interactive users do
not grow a beard while waiting for the next interaction. If you unleash
parallelism on a single job, which is sometimes the way to crank big jobs
through fastest a small number of jobs at a time on a machine with no
interactive users, then the interactive users grow a beard and it turns
white.
So one way to still get something like full utilization of all but the
headroom is to use a process manager, such as the concurrent manager from
Oracle?s very own e-Business suite. So instead of unleashing jobs with a
parallel degree higher than 1, you configure something to try to run batch
jobs but leave enough headroom to avoid the aforementioned beard growth.
Now in pure batch, as told in an eloquent paper by Cary Millsap, it takes
just about 2 jobs per processor to tie them up. Now unlike some of the
actual mathematical laws and theorems Cary from time to time references,
this is just a thumbrule of experience based on the coincidence, which might
vary some, that jobs batch jobs preempt themselves from the cpu to do i/o
about half the time. (His paper really explains this quite nicely, and that
is only an approximation.) So whatever concurrency of jobs you set up to get
parallellism by number of jobs instead of parallelism within a single job,
remember to leave the headroom you need.
If you have some ?workshifts? where interactive users are absent, and you
have some whopping big job that needs all your horsepower to finish before
the interactive user population returns, then you *might* stop submitting
new jobs through your hypothecated process manager and turn that bad boy
loose using the whole machine. But usually you just up the number of jobs
run concurrently to eat up the headroom and take that back down so the
headroom returns before the user population. Workshifts might vary by day,
timezone, and various and sundry other things.
In summary, you probably want degree 1 on OLTP systems, and to manage
utilization by managing the number of batch or psuedo batch jobs that are
run in parallel with each other.
Regards,
mwf
_____
From: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx]
On Behalf Of Juan Miranda
Sent: Wednesday, December 02, 2009 11:52 AM
To: oracle-l@xxxxxxxxxxxxx
Subject: Parallel procesing configuration.
Hi
With today multicore servers, parallel query is very important to get the
max performance from a server.
It´s common to see 16 core servers using only one of them?
Do you put some little parallelism on OLTP databases?
Where do you configure it? At table level? Instance level?
Please, share your kwnoledge, interesting docs, hints, etc about this
complex topic.
This is my biggest question about Oracle configuration.
Thanks.
Juan
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