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Re: Several CPUs and the parallel option

From: Andy <andy.spaven_at_eps-hq.co.uk>
Date: Mon, 29 Jul 2002 16:58:13 +0100
Message-ID: <eyd19.208$9R.1011965@newsr2.u-net.net>


Rick

I think Steve may have identified the clincher here. Oracle Parallel Server (OPS) is completely different to Parallel Query Option (PQO) (though I think it's had a name change in Ora9???).

To get the app to make use of PQO, you can do one of several things - I can think of two extremes

  1. Change default degree of parallel (DOP) using ALTER TABLE my_big_table PARALLEL n Assuming you've got stats then Oracle will automatically use this parallel value in ALL operations on this table. This can be a bit like using a sledgehammer to crack a nut.... unless all the nuts are rock hard. This has the knock on effect of spawning the number of PQO servers for each SQL statement concurrently running against this table (subject to max limit on PQO servers in init.ora).
  2. Put hints into those SQL statements that you wish to take advantage of PQO using /*+ PARALLEL(table_name_or_alias, n) */ This means code changes but limits the effects to where you really want PQO.

Remember that you'll need to have data in multiple extents before Oracle can use PQO - each PQO server is given an extent to work. Realistically though to get the best performance you'll want to spread the data over as many disks as possible using Oracle or OS stripping.

Andy

"Steve" <smontgomerie_at_hotmail.com> wrote in message news:156709aa.0207290435.68932bda_at_posting.google.com...
> > When I start instance, I get a message "...with the parallel option".
> > But when I set the parallel option on in the init.ora file, the
> > instance won't start.
> >
>
> you're not trying to start up with parllel_server = true are you? If
> so this is OPS/RAC and is a different ball game then paralle query
> option (pwo)
>
> steve
Received on Mon Jul 29 2002 - 10:58:13 CDT

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