From: Tomas Vondra <tomas.vondra@2ndquadrant.com>
To: Kyotaro HORIGUCHI <horiguchi.kyotaro@lab.ntt.co.jp>
Cc: jeff.janes@gmail.com
Cc: sfrost@snowman.net
Cc: pgsql-hackers@postgresql.org
Subject: Re: multivariate statistics / patch v6
Date: Fri, 15 May 2015 19:41:15 +0200
Message-ID: <55562FBB.7020103@2ndquadrant.com> (raw)
In-Reply-To: <20150515.152936.83796179.horiguchi.kyotaro@lab.ntt.co.jp>
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<20150513.173159.102421446.horiguchi.kyotaro@lab.ntt.co.jp>
<55547A86.8020400@2ndquadrant.com>
<20150515.152936.83796179.horiguchi.kyotaro@lab.ntt.co.jp>
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Hello,
On 05/15/15 08:29, Kyotaro HORIGUCHI wrote:
> Hello,
>
> At Thu, 14 May 2015 12:35:50 +0200, Tomas Vondra
<tomas.vondra@2ndquadrant.com> wrote in <55547A86.8020400@2ndquadrant.com>
...
>
>> Regarding the functional dependencies - you're right there's room for
>> improvement. For example it only works with dependencies between pairs
>> of columns, not multi-column dependencies. Is this what you mean by
>> incomplete?
>
> No, It overruns dependencies->deps because build_mv_dependencies
> stores many elements into dependencies->deps[n] although it
> really has a room for only one element. I suppose that you paused
> writing it when you noticed that the number of required elements
> is unknown before finising walk through all pairs of
> values. palloc'ing numattrs^2 is reasonable enough as POC code
> for now. Am I looking wrong version of patch?
>
> - dependencies = (MVDependencies)palloc0(sizeof(MVDependenciesData))
> + dependencies = (MVDependencies)palloc0(sizeof(MVDependenciesData) +
> + sizeof(MVDependency) * numattrs * numattrs);
Actually, looking at this a bit more, I think the current behavior is
correct. I assume the line is from build_mv_dependencies(), but the
whole block looks like this:
if (dependencies == NULL)
{
dependencies = (MVDependencies)palloc0(sizeof(MVDependenciesData));
dependencies->magic = MVSTAT_DEPS_MAGIC;
}
else
dependencies = repalloc(dependencies,
offsetof(MVDependenciesData, deps) +
sizeof(MVDependency) * (dependencies->ndeps + 1));
which allocates space for a single element initially, and then extends
that when other dependencies are added.
--
Tomas Vondra http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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Cc: tomas.vondra@2ndquadrant.com, horiguchi.kyotaro@lab.ntt.co.jp, jeff.janes@gmail.com, sfrost@snowman.net
Subject: Re: multivariate statistics / patch v6
In-Reply-To: <55562FBB.7020103@2ndquadrant.com>
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