Re: What is Parallel DML?

"Billy Verreynne" <vslabs_at_onwe.co.za> wrote in message news:<9jj16k$dpk$1_at_ctb-nnrp1.saix.net>...
> Howard J. Rogers wrote
>
> >That doesn't get around the fact that at any one moment, only a single
> >process can be serviced by a single CPU, regardless of capacity.
>
> What moment? Per second? Many processes can be run on the CPU per second. Per
> milisecond? Per nanosecond? This argument is nonsensical.
>
> A single CPU can service many processes simultanously. And if you look closely
> at the design of the new generation CPUs, even the "fact" that a CPU can only
> executed a single instruction in a single point in time, no longer holds true.
>
> > >effective use, but only one of those slave process can actually have time
> > >on the CPU at any given moment. And *that's* the reason my query slowed down
> > >with a degree of parallelism of 2 -having to perform a context switch
> > >between two processes on the one CPU is expensive.
>
> Context switching is _not_ the issue.
>
> > >Threads are a different game again, since there is no context switch when
> > >switching between threads within the one process.
>
> So PQs are not threads on a platform like NT? Or because PQ are threads on NT,
> it works on a single CPU NT machine, but not when running Linux with Oracle on
> that exact same machine? You are arguing in circles.
>
> The fact is that PQ does work on a single CPU platform. Period. From a 200Mhz
> Pentium running Oracle 7.3 to a massive parallel cluster of single CPU Unix
> nodes running Oracle Parallel Server. Been there. Done that. Have the t-shirt.
>
> >Your mileage may vary: mine never has.
>
> Yeah, that is always a problem with closed minds that never want to understand
> and tweak for better mileage.

Not only that parallel DML works on single CPU box, but I think that bigger speed improvement can be made not with more CPUs, but with table spread across more tablespaces on different drives using Parallel Option for Enterprise
server.
Disk drive access is usually more time consuming, than limitations of processor capacity. It's obvious that this applies only to properly sized boxes, not for dababase servers with UltraWide SCSI drives and one Intel 486DX CPU. :-)

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Dusan Bolek, Ing.
Oracle team leader