| From: | Ants Aasma <ants(dot)aasma(at)eesti(dot)ee> |
|---|---|
| To: | Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com> |
| Cc: | Tatsuo Ishii <ishii(at)postgresql(dot)org>, Robert Haas <robertmhaas(at)gmail(dot)com>, david(at)pgmasters(dot)net, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, petr(at)2ndquadrant(dot)com, Jeff Janes <jeff(dot)janes(at)gmail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: multivariate statistics (v19) |
| Date: | 2016-08-10 13:29:04 |
| Message-ID: | CA+CSw_tQnxyGxiL4AnVmHD8MHpCTyScmHOHX-s_LVsS7+vOPDQ@mail.gmail.com |
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On Wed, Aug 3, 2016 at 4:58 AM, Tomas Vondra
<tomas(dot)vondra(at)2ndquadrant(dot)com> wrote:
> 2) combining multiple statistics
>
> I think the ability to combine multivariate statistics (covering different
> subsets of conditions) is important and useful, but I'm starting to think
> that the current implementation may not be the correct one (which is why I
> haven't written the SGML docs about this part of the patch series yet).
While researching this topic a few years ago I came across a paper on
this exact topic called "Consistently Estimating the Selectivity of
Conjuncts of Predicates" [1]. While effective it seems to be quite
heavy-weight, so would probably need support for tiered optimization.
[1] https://courses.cs.washington.edu/courses/cse544/11wi/papers/markl-vldb-2005.pdf
Regards,
Ants Aasma
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