Re: Re: max parallel query

If you want rules of thumb, then take CPU_COUNT+1 up to CPU_COUNT *2.

I think LIO & PIO ratio is irrelevant, the most important is whether you are able to construct optimal parallel execution plan, e.g. avoid excessive parallel slave messaging & waiting. This is mostly design and SQL issue.

The number mount points is irrelevant novadays as well IMHO, especially when you're using async IO, SANs & SAME like architecture. The only thing what comes into my mind where splitting into mount points (thus different file systems) helps performance wise, is that with more file systems you got more file system locks and you can spread contention for these locks that way.

Tanel.

• Original Message ----- To: "Multiple recipients of list ORACLE-L" <ORACLE-L_at_fatcity.com> Sent: Thursday, September 18, 2003 9:34 PM

> i know there are no magic formulas, but im hoping for something better
than trial and error. i would assume that parallel query helps most when:
>
> 1. are doing work off of multiple mount points.
> 2. Have alot more LIOs to perform than PIOs(such as sorts).
>
> am i close on this?
> >
> > From: "M Rafiq" <rafiq9857_at_hotmail.com>
> > Date: 2003/09/18 Thu PM 01:34:44 EDT
> > To: Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com>
> > Subject: Re: max parallel query
> >
> > Tanel,
> > You are right. There is a param parallel_automatic(I don't remember
exact
> > name as I don't have access to database) which should be set to true and
let
> > system decide how many pq slave to be used. For max_parallel_server
default
> > is 5 and can be set to higher number which memory and cpu can handle.
It
> > is faster because it uses all system resources at a given time.
> >
> > Rarallel process can be used for large batch jobs during off-peak time.
> >
> > Regards
> > Rafiq
> >
> >
> > Reply-To: ORACLE-L_at_fatcity.com
> > To: Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com>
> > Date: Thu, 18 Sep 2003 08:39:44 -0800
> >
> > There is no simple magic formula how many parallel slaves you should
have.
> > It all depends on your CPU and IO utilization. Yes, utilization, because
if
> > your CPUs or IO are running at their limits already, you won't benefit
from
> > parallel execution at all. In fact PX may make the situation even worse,
> > because it's designed to give you the results the fastest way, not the
most
> > efficient way.
> >
> > Tanel.
> >
> > ----- Original Message -----
> > To: "Multiple recipients of list ORACLE-L" <ORACLE-L_at_fatcity.com>
> > Sent: Thursday, September 18, 2003 6:15 PM
> >
> >
> > > We run multiple instances on the same server. My understanding is
> > max_parallel_servers should be set to 4 x CPU. We have 4 CPUs which
means
> > 16.
> > >
> > > however, does this take into account multiple instances on the same
> > server?
> > >
> > >
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-- 
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-- 
Author: Tanel Poder
  INET: tanel.poder.003_at_mail.ee

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