Subject: Re: PATCH: multivariate histograms and MCV lists
To: Adrien Nayrat <adrien.nayrat@dalibo.com>,
 Pg Hackers <pgsql-hackers@postgresql.org>
References: <dfdac334-9cf2-2597-fb27-f0fb3753f435@2ndquadrant.com>
 <31ee8686-6d62-7f10-4129-7580ec74a710@dalibo.com>
From: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Message-ID: <b3688203-7c5d-2d7e-58b6-a6bb04f29b5c@2ndquadrant.com>
Date: Sat, 26 Aug 2017 16:14:24 +0200
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On 08/17/2017 12:06 PM, Adrien Nayrat wrote:>
> Hello,
> 
> There is no check of "statistics type/kind" in
> pg_stats_ext_mcvlist_items and pg_histogram_buckets.
> 
> select stxname,stxkind from pg_statistic_ext ; stxname  | stxkind 
> -----------+--------- stts3     | {h} stts2     | {m}
> 
> So you can call :
> 
> SELECT * FROM pg_mcv_list_items((SELECT oid FROM pg_statistic_ext
> WHERE stxname = 'stts3'));
> 
> SELECT * FROM pg_histogram_buckets((SELECT oid FROM pg_statistic_ext
> WHERE stxname = 'stts2'), 0);
> 
> Both crashes.
> 

Thanks for the report, this is clearly a bug. I don't think we need to
test the stxkind, but rather a missing check that the requested type is
actually built.

> Unfotunately, I don't have the knowledge to produce a patch :/
> 
> Small fix in documentation, patch attached.
> 

Thanks, will fix.

regards

-- 
Tomas Vondra                  http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services


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