Re: WIP: multivariate statistics / proof of concept

On 29/10/14 10:41, David Rowley wrote:
> On Mon, Oct 13, 2014 at 11:00 AM, Tomas Vondra <tv(at)fuzzy(dot)cz
>
> The last point is really just "unfinished implementation" - the syntax I
> propose is this:
>
> ALTER TABLE ... ADD STATISTICS (options) ON (columns)
>
> where the options influence the MCV list and histogram size, etc. The
> options are recognized and may give you an idea of what it might do, but
> it's not really used at the moment (except for storing in the
> pg_mv_statistic catalog).
>
>
>
> I've not really gotten around to looking at the patch yet, but I'm also
> wondering if it would be simple include allowing functional statistics
> too. The pg_mv_statistic name seems to indicate multi columns, but how
> about stats on date(datetime_column), or perhaps any non-volatile
> function. This would help to solve the problem highlighted here
> http://www.postgresql.org/message-id/CAApHDvp2vH=7O-gp-zAf7aWy+A-WHWVg7h3Vc6=5pf9Uf34DhQ@mail.gmail.com
> . Without giving it too much thought, perhaps any expression that can be
> indexed should be allowed to have stats? Would that be really difficult
> to implement in comparison to what you've already done with the patch so
> far?
>

I would not over-complicate requirements for the first version of this,
I think it's already complicated enough.

Quick look at the patch suggests that it mainly needs discussion about
design and particular implementation choices, there is fair amount of
TODOs and FIXMEs. I'd like to look at it too but I doubt that I'll have
time to do in depth review in this CF.

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