Re: Performance degradation in TPC-H Q18

On Mon, Mar 6, 2017 at 3:32 PM, Andres Freund <andres(at)anarazel(dot)de> wrote:
>> I think DEBUG1 is far too high for something that could occur with
>> some frequency on a busy system; I'm fairly strongly of the opinion
>> that you ought to downgrade that by a couple of levels, say to DEBUG3
>> or so.
>
> I actually planned to remove it entirely, before committing. It was more
> left in for testers to be able to see when the code triggers.

Oh, OK. That'd be fine too.

> FWIW, I played with some better mixing, and it helps a bit with
> accurately sized hashtables and multiple columns.
>
> What's however more interesting is that a better mixed IV and/or better
> iteration now *slightly* *hurts* performance with grossly misestimated
> sizes, because resizing has to copy more rows... Not what I predicted.

I don't quite follow this.

--
Robert Haas
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