Re: Initial prefetch performance testing

Gregory Stark wrote:
>
> Ron Mayer <rm_pg(at)cheapcomplexdevices(dot)com> writes:
>
> > For example, on our sites hosted with Amazon's compute cloud (a great
> > place to host web sites), I know nothing about spindles, but know
> > about Amazon Elastic Block Store[2]'s and Instance Store's[1]. I
> > have some specs and are able to run benchmarks on them; but couldn't
> > guess how many spindles my X% of the N-disk device that corresponds
> > to.
>
> Well I don't see how you're going to guess how much prefetching is optimal for
> those environments either...
>
> > For another example, some of our salesguys with SSD drives
> > have 0 spindles on their demo machines.
>
> Sounds to me like you're finding it pretty intuitive. Actually you would want
> "1" because it can handle one request at a time. Actually if you have a
> multipath array I imagine you would want to think of each interface as a
> spindle because that's the bottleneck and you'll want to keep all the
> interfaces busy.

I assume everyone would want at least one because you would want the
page to be prefetched while you are processing the existing page. I
think a larger problem is that it is likely the page prefetch will take
longer than processing the existing page, which might mean that you need
to prefetch a few pages ahead to allow read reordering for better
performance.

--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com

+ If your life is a hard drive, Christ can be your backup. +