Re: Parallel Seq Scan

From: Daniel Bausch <bausch(at)dvs(dot)tu-darmstadt(dot)de>
To: pgsql-hackers(at)postgresql(dot)org
Subject: Re: Parallel Seq Scan
Date: 2015-01-27 07:02:37
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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)

MSc. Daniel Bausch
Research Assistant (Computer Science)
Technische Universität Darmstadt

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