Re: WIP: multivariate statistics / proof of concept

From: Tomas Vondra <tv(at)fuzzy(dot)cz>
To: pgsql-hackers(at)postgresql(dot)org
Subject: Re: WIP: multivariate statistics / proof of concept
Date: 2014-11-10 02:34:52
Message-ID: 5460244C.8080109@fuzzy.cz
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On 30.10.2014 10:23, David Rowley wrote:
> On Thu, Oct 30, 2014 at 12:21 AM, Tomas Vondra <tv(at)fuzzy(dot)cz
> <mailto:tv(at)fuzzy(dot)cz>> wrote:
>
> Dne 29 Říjen 2014, 10:41, David Rowley napsal(a):
> > 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]
> >
>
> 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 :-(
>
>
> It should be a pretty simple fix, just use the files and line
> numbers from the above. It's just a problem that in those 3 places
> you're declaring an array of a variable size, which is not allowed in
> C89. The thing to do instead would just be to palloc() the size you
> need and the pfree() it when you're done.

Attached is a patch that should fix these issues.

The bad news is there are a few installcheck failures (and were in the
previous patch, but I haven't noticed for some reason). Apparently,
there's some mixup in how the patch handles Var->varno in some causes,
causing issues with a handful of regression tests.

The problem is that is_mv_compatible (checking whether the condition is
compatible with multivariate stats) does this

if (! ((varRelid == 0) || (varRelid == var->varno)))
return false;

/* Also skip special varno values, and system attributes ... */
if ((IS_SPECIAL_VARNO(var->varno)) ||
(! AttrNumberIsForUserDefinedAttr(var->varattno)))
return false;

assuming that after this, varno represents an index into the range
table, and passes it out to the caller.

And the caller (collect_mv_attnums) does this:

RelOptInfo *rel = find_base_rel(root, varno);

which fails with errors like these:

ERROR: no relation entry for relid 0
ERROR: no relation entry for relid 1880

or whatever. What's even stranger is this:

regression=# SELECT table_name, is_updatable, is_insertable_into
regression-# FROM information_schema.views
regression-# WHERE table_name = 'rw_view1';
ERROR: no relation entry for relid 0
regression=# SELECT table_name, is_updatable, is_insertable_into
regression-# FROM information_schema.views
regression-# ;
regression=# SELECT table_name, is_updatable, is_insertable_into
regression-# FROM information_schema.views
regression-# WHERE table_name = 'rw_view1';
table_name | is_updatable | is_insertable_into
------------+--------------+--------------------
(0 rows)

regression=# explain SELECT table_name, is_updatable, is_insertable_into
FROM information_schema.views
WHERE table_name = 'rw_view1';
ERROR: no relation entry for relid 0

So, the query fails. After removing the WHERE clause it works, and this
somehow fixes the original query (with the WHERE clause). Nevertheless,
I still can't do explain on the query.

Clearly, I'm doing something wrong. I suspect it's caused either by
conditions involving function calls, or the fact that the view is a join
of multiple tables. But what?

For simple queries (single table, ...) it seems to be working fine.

regards
Tomas

Attachment Content-Type Size
multivar-stats-v2.patch text/x-diff 161.6 KB

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