Re: Seq scans status update

Great. Based on this, do you have a patch that is ready to apply.

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Heikki Linnakangas wrote:
> Heikki Linnakangas wrote:
> > In any case, I'd like to see more test results before we make a
> > decision. I'm running tests with DBT-2 and a seq scan running in the
> > background to see if the cache-spoiling effect shows up. I'm also trying
> > to get hold of some bigger hardware to run on. Running these tests takes
> > some calendar time, but the hard work has already been done. I'm going
> > to start reviewing Jeff's synchronized scans patch now.
>
> Here are the results of the DBT-2 tests:
>
> http://community.enterprisedb.com/seqscan/imola/
>
> In each of these tests, at the end of rampup a script is started that
> issues a "SELECT COUNT(*) FROM stock" in a loop, with 2 minute delay
> between end of previous query and start of next one.
>
> The patch makes the seq scans go significantly faster. In the 1 hour
> test period, the patched tests perform roughly 30-100% as many selects
> as unpatched tests.
>
> With 100 and 105 warehouses, it also significantly reduces the impact of
> the seq scan on other queries; response times are lower with the patch.
> With 120 warehouses the reduction of impact is not as clear, but when
> you plot the response times it's still there (the plots on the "response
> times charts"-page are useless because they're overwhelmed by the
> checkpoint spike).
>
> --
> Heikki Linnakangas
> EnterpriseDB http://www.enterprisedb.com
>
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Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
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