Re: Monitoring parallelism

If were expecting your queries to automatically start running in parallel then I don't think that is true.
Though things change from version to version. The parameters that you are talking about "parallel_max_servers"
are there to "enable" parallelism. That statement however does not mean that things will automatically
start running in parallel. Thus if you set parallel_max_servers = 0, you would probably be not able to use
the PQO.
Though I did state that if you put the specify parallel clause in the create table / alter table statement .. then
you would be able to use parallelism. I however would not recommend this. Be aware that if you set this
clause at the table level, Oracle will start doing parallel full table scans much more than using indexes, which
you might or *might not* want.
You should according to me use this feature by providing hints (for parallel) in your queries, if you think that
the query will benefit from it. Which is the reason why I recommended reading up a perf tuning manual.

***
Try Hi Performance SQL ... book by Harrison for a start. I'm sure Tom Kyte must have provided some examples in his book and website (asktom.oracle.com .. search parallel) about using Parallel Query. Also, look at this link: http://www.jlcomp.demon.co.uk/ind_pqo.html Jonathan has written a nice piece about PQ. ***

Anurag

"Rick Denoire" <100.17706_at_germanynet.de> wrote in message news:kguvlucuabrgvbk2toqn6ts01dn0mstfaj_at_4ax.com...
> "Anurag Varma" <avdbi_at_hotmail.com> wrote:
>
> >Queries are parallelized when you tell Oracle to parallelize them ...
> >
> >example:
> >Select /*+ ordered PARALLEL(tab1 4) FULL(tab1) */
> >from tab1, tab2
> >where tab1.col1 = tab2.col1
> >/
> >
> >Or you specify the degree of parallelism on the table level:
> >create table tab1 .....
> >parallel 4
> >/
> >
> >or you can rebuild index in parallel ...
> >
> >there are other various instances ....
> >
> >Before you do anything, please get your "parallel" fundamentals right by referring to a
> >good perf tuning book .. or refer to the perf tuning documentation by oracle.
> >Otherwise, you might do more harm to the system .. than good.
> >
>
> I was trying to clear exaxtly that point while I was reading the
> documentation... I was not sure, but as I understood, it is enough to
> switch on parallelism in the init.ora file.
>
> What you are saying is that this is not enough. So I should, for
> example, change the degree of paralellism of the tables
> *additionally*. Right? Please confirm!
>
> (By the way, I also understood that changing the degree of parallelism
> alone would be enough too - it seems that i misunderstood
> everything!).
>
> Thanks a lot
> Rick
>
Received on Sun Aug 18 2002 - 18:54:24 CDT