Re: Memory prefetching while sequentially fetching from SortTuple array, tuplestore

On 3 September 2015 at 07:24, Peter Geoghegan <pg(at)heroku(dot)com> wrote:

> On Wed, Sep 2, 2015 at 7:12 AM, Andres Freund <andres(at)anarazel(dot)de> wrote:
> > What worries me about adding explicit prefetching is that it's *highly*
> > platform and even micro-architecture dependent. Why is looking three
> > elements ahead the right value?
>
> Because that was the fastest value following testing on my laptop. You
> are absolutely right to point out that this isn't a good reason to go
> with the patch -- I share your concern. All I can say in defense of
> that is that other major system software does the same, without any
> regard for the underlying microarchitecture AFAICT. So, yes,
> certainly, more testing is required across a reasonable cross-section
> of platforms to justify the patch.
>

FWIW someone else found 3 to be good on the platform they tested on:
http://www.naftaliharris.com/blog/2x-speedup-with-one-line-of-code/

Peter, would you be able to share the test case which you saw the speedup
on. So far I've been unable to see much of an improvement.

Regards

David Rowley

--
David Rowley http://www.2ndQuadrant.com/
<http://www.2ndquadrant.com/>
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