Re: Multi-column distinctness.

On 5 September 2015 at 20:46, Bruce Momjian <bruce(at)momjian(dot)us> wrote:

> On Fri, Aug 28, 2015 at 05:33:34PM +0900, Kyotaro HORIGUCHI wrote:
> > Hello, this patch enables planner to be couscious of inter-column
> > correlation.
> >
> > Sometimes two or more columns in a table has some correlation
> > which brings underestimate, which leads to wrong join method and
> > ends with slow execution.
> >
> > Tomas Vondra is now working on heavily-equipped multivariate
> > statistics for OLAP usage. In contrast, this is a lightly
> > implemented solution which calculates only the ratio between a
> > rows estimated by current method and a actual row number. I think
> > this doesn't conflict with his work except the grammar part.
>
> I am very glad multi-variate statistics are being addressed. I think
> this is our most common cause of optimizer failures.
>

Glad to see you agree.

Why have you said this on *this* patch, when Tomas' patch has been very
obviously addressing this problem since January, with very little traction.

Please add your backing to Tomas' patch.

--
Simon Riggs http://www.2ndQuadrant.com/
<http://www.2ndquadrant.com/>
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