Re: WIP: multivariate statistics / proof of concept

On 12 October 2014 23:00, Tomas Vondra <tv(at)fuzzy(dot)cz> wrote:

> It however seems to be working sufficiently well at this point, enough
> to get some useful feedback. So here we go.

This looks interesting and useful.

What I'd like to check before a detailed review is that this has
sufficient applicability to be useful.

My understanding is that Q9 and Q18 of TPC-H have poor plans as a
result of multi-column stats errors.

Could you look at those queries and confirm that this patch can
produce better plans for them?

If so, I will work with you to review this patch.

One aspect of the patch that seems to be missing is a user declaration
of correlation, just as we have for setting n_distinct. It seems like
an even easier place to start to just let the user specify the stats
declaratively. That way we can split the patch into two parts. First,
allow multi column stats that are user declared. Then add user stats
collected by ANALYZE. The first part is possibly contentious and thus
a good initial focus. The second part will have lots of discussion, so
good to skip for a first version.

--
Simon Riggs http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services