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Date: Wed, 29 Oct 2014 12:21:08 +0100
Subject: Re: WIP: multivariate statistics / proof of concept
From: "Tomas Vondra" <tv@fuzzy.cz>
To: "David Rowley" <dgrowleyml@gmail.com>
Cc: "Tomas Vondra" <tv@fuzzy.cz>,
 "PostgreSQL-development" <pgsql-hackers@postgresql.org>
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Dne 29 Říjen 2014, 10:41, David Rowley napsal(a):
>
> 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 don't know, but it seems mostly orthogonal to what the patch aims to do.
If we add collecting statistics on expressions (on a single column), then I'd
expect it to be reasonably simple to add this to the multi-column case.

There are features like join stats or range type stats, that are probably
more directly related to the patch (but out of scope for the initial
version).

> I'm quite interested in reviewing your work on this, but it appears that
> some of your changes are not C89:
>
>  src\backend\commands\analyze.c(3774): error C2057: expected constant
> expression [D:\Postgres\a\postgres.vcxproj]
>  src\backend\commands\analyze.c(3774): error C2466: cannot allocate an
> array of constant size 0 [D:\Postgres\a\postgres.vcxproj]
>  src\backend\commands\analyze.c(3774): error C2133: 'indexes' : unknown
> size [D:\Postgres\a\postgres.vcxproj]
>  src\backend\commands\analyze.c(4302): error C2057: expected constant
> expression [D:\Postgres\a\postgres.vcxproj]
>  src\backend\commands\analyze.c(4302): error C2466: cannot allocate an
> array of constant size 0 [D:\Postgres\a\postgres.vcxproj]
>  src\backend\commands\analyze.c(4302): error C2133: 'ndistincts' : unknown
> size [D:\Postgres\a\postgres.vcxproj]
>  src\backend\commands\analyze.c(4775): error C2057: expected constant
> expression [D:\Postgres\a\postgres.vcxproj]
>  src\backend\commands\analyze.c(4775): error C2466: cannot allocate an
> array of constant size 0 [D:\Postgres\a\postgres.vcxproj]
>  src\backend\commands\analyze.c(4775): error C2133: 'keys' : unknown size
> [D:\Postgres\a\postgres.vcxproj]
>
> The compiler I'm using is a bit too stupid to understand the C99 syntax.
>
> I guess you'd need to palloc() these arrays instead in order to comply
> with
> the project standards.
>
> http://www.postgresql.org/docs/devel/static/install-requirements.html
>
> I'm going to sign myself up to review this, so probably my first feedback
> would be the compiling problem.

I'll look into that. The thing is I don't have access to MSVC, so it's a bit
difficult to spot / fix those issues :-(

regards
Tomas


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