Re: Re: max parallel query

If different mount point means different disk spindle group or different disk array, then of course, your performance will be improved, but if we talk about the same box, same number of disks just split to two or three, you probably won't get any performance increase. One disk spindle still remains one disk spindle, no matter how you split them.

Tanel.

• Original Message ----- To: "Multiple recipients of list ORACLE-L" <ORACLE-L_at_fatcity.com> Sent: Friday, September 19, 2003 12:44 AM

> hmmm... when i run statspack during a big load. most of my waits are from
> redo log waits and read from a staging datafile. we have all of our
> datafiles on the same I/O mount. We are using a Network Appliance back end
> with asynch I/O.
>
> are you telling me that putting these files on seperate mount points will
> have no effect? I dont quite follow asynch I/O. I dont have much of a hard
> ware OS background.
>
> I cant find any docs or articles on how to tune Parallel Operations. All I
> see are basic syntax. Do you know of any?
> ----- Original Message -----
> To: "Multiple recipients of list ORACLE-L" <ORACLE-L_at_fatcity.com>
> Sent: Thursday, September 18, 2003 5:24 PM
>
>
> > 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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> > > > > Author: <rgaffuri_at_cox.net
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> > > > >
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-- 
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-- 
Author: Tanel Poder
  INET: tanel.poder.003_at_mail.ee

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