Re: Parallel Seq Scan

From: David Fetter <david(at)fetter(dot)org>
To: Daniel Bausch <bausch(at)dvs(dot)tu-darmstadt(dot)de>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: Parallel Seq Scan
Date: 2015-01-27 14:54:48
Message-ID: 20150127145448.GA3788@fetter.org
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On Tue, Jan 27, 2015 at 08:02:37AM +0100, Daniel Bausch wrote:
> Hi PG devs!
>
> Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> writes:
>
> >> Wait for first IO, issue second IO request
> >> Compute
> >> Already have second IO request, issue third
> >> ...
> >
> >> We'd be a lot less sensitive to IO latency.
> >
> > It would take about five minutes of coding to prove or disprove this:
> > stick a PrefetchBuffer call into heapgetpage() to launch a request for the
> > next page as soon as we've read the current one, and then see if that
> > makes any obvious performance difference. I'm not convinced that it will,
> > but if it did then we could think about how to make it work for real.
>
> Sorry for dropping in so late...
>
> I have done all this two years ago. For TPC-H Q8, Q9, Q17, Q20, and Q21
> I see a speedup of ~100% when using IndexScan prefetching + Nested-Loops
> Look-Ahead (the outer loop!).
> (On SSD with 32 Pages Prefetch/Look-Ahead + Cold Page Cache / Small RAM)

Would you be so kind as to pass along any patches (ideally applicable
to git master), tests, and specific measurements you made?

Cheers,
David.
--
David Fetter <david(at)fetter(dot)org> http://fetter.org/
Phone: +1 415 235 3778 AIM: dfetter666 Yahoo!: dfetter
Skype: davidfetter XMPP: david(dot)fetter(at)gmail(dot)com

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