Re: What is Parallel DML?

"Billy Verreynne" <vslabs_at_onwe.co.za> wrote in message news:9jcmi1$nrr$1_at_ctb-nnrp1.saix.net...
> "Howard J. Rogers" <howardjr_at_www.com> wrote
>
> > The short story is that you are going to get multiple server processes
> > updating different data blocks at the same time. Accordingly, whatever
 DML
> > it is that you are performing takes much less time to perform.
> >
> > Totally pointless on a single CPU box, really, since only one process
 can
> > run on a CPU at any one nanosecond, but in a multi-CPU and
 multi-Gigabyte
> > database, it can make a lot of difference.
>
> Bull. If there is one thing that really makes me want to swing my lead
 pipe,
> even when I had my first early morning cup, is ignorance shared as a pearl
> of wisdom.
>

It wasn't offered as a pearl of wisdom, but as a result of some testing, and some extensive reading of the relevant documentation.... which, going all the way back to Oracle 7 docs, states :

"The parallel query feature can dramatically improve performance for data-intensive operations associated with decision support applications or very large database environments. Symmetric multiprocessing (SMP), clustered, or massively parallel systems gain the largest performance benefits from the parallel query feature because query processing can be effectively split up among many CPUs on a single system"

...er, which rather implies that the number of CPUs has some relevance for the matter of whether or not it is effective.

> It makes a difference - a HUGE difference. Go and read up some on before
> making statements like that.
>
> It is a FANTASY story that PQ or parallel processing does not work, or
 does
> not work well, on a single CPU box.
>

I've actually had a query *slow down* by specifying a degree of parallelism on a single CPU box. And that wasn't a fantasy.

HJR
> --
> Billy
>
>
>
>
Received on Sat Jul 21 2001 - 22:58:53 CDT