Re: Multi-column distinctness.

Hello,

On 09/06/2015 10:24 AM, Simon Riggs wrote:
> On 28 August 2015 at 09:33, Kyotaro HORIGUCHI
> <horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp
> <mailto:horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp>> wrote:
>
> 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 think it very obviously does conflict, so I don't see this patch as
> appropriate.
>
> If you think a cut version of Tomas' patch is appropriate, then the
> usual response is to give a review that says "Tomas, I think a cut down
> version is appropriate here, can we reduce the scope of this patch for
> now?". If you have done that and he refuses to listen, then a separate
> patch version is appropriate. Otherwise we should just reject this
> second patchset to avoid confusion and to avoid encouraging people to
> take this approach.

FWIW Horiguchi-san is one of the few people who actually took time to
review the multivariate stats patch, and I don't quite see this patch as
conflicting with the multivariate one.

It implements a small subset of the (much larger) multivariate stats
patch, and reusing it within my patch should not be a big deal.
Actually, this type of statistics was proposed by Horiguchi-san himself,
and the multivariate patch does not implement it yet (although I intend
to address that soon).

So no conflict here. Of course, we need to be a bit careful to make it
compatible (especially the syntax part).

kind regards

--
Tomas Vondra http://www.2ndQuadrant.com/
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