Re: What is Parallel DML?

"Howard J. Rogers" <howardjr_at_www.com> wrote in message

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

Multiple CPU's increases capacity - which is what parallel processing needs. However, you still have capacity on a single CPU. Thus you can effectively use parallel processing on a single CPU machine.

Saying that parallel procesing does not work on a single CPU, is like saying that multithreading one a single CPU does not work. Neither is true. What is true that you have less capacity on a single CPU box which has less capacity than a dual CPU box, which has less capacity than a quad CPU box, and so on..

Many database platforms runs their CPU/CPUs at far less than even 50% capacity. Which means that there is wasted CPU time that can very effectively be put to use - and parallel processing is one of the better methods to increase performance and make proper use of CPU capacity.

> 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.

The reason for that is that the amount of parallelism you used exceeded CPU capacity. And that can be done without even having to resort to parallel query or DML processing.

--
Billy