Horton

Re: PATCH: multivariate histograms and MCV lists

Tomas Vondra <tomas.vondra@2ndquadrant.com>

View thread View on postgr.es
From: Tomas Vondra <tomas.vondra@2ndquadrant.com>
To: Adrien Nayrat <adrien.nayrat@dalibo.com>, Pg Hackers <pgsql-hackers@postgresql.org>
Date: 2017-08-26T14:14:24Z
Lists: pgsql-hackers 

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

Commits

  1. Convert pre-existing stats_ext tests to new style

  2. Add support for multivariate MCV lists

  3. Improve ANALYZE's strategy for finding MCVs.

  4. Clone extended stats in CREATE TABLE (LIKE INCLUDING ALL)

  5. Try again to fix accumulation of parallel worker instrumentation.

  6. Adjust psql \d query to avoid use of @> operator.

  7. Message style fixes

  8. Add security checks to selectivity estimation functions