Re: [HACKERS] PATCH: multivariate histograms and MCV lists

On 08/14/2017 12:48 AM, Tomas Vondra wrote:
> Hi all,
>
> For PostgreSQL 10 we managed to get the basic CREATE STATISTICS bits in
> (grammar, infrastructure, and two simple types of statistics). See:
>
>     https://commitfest.postgresql.org/13/852/
>
> This patch presents a rebased version of the remaining parts, adding more
> complex statistic types (MCV lists and histograms), and hopefully some
> additional improvements.
>
> The code was rebased on top of current master, and I've made various
> improvements to match how the committed parts were reworked. So the basic idea
> and shape remains the same, the tweaks are mostly small.
>
>
> regards
>
>
>
>

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.

Unfotunately, I don't have the knowledge to produce a patch :/

Small fix in documentation, patch attached.


Thanks!

--
Adrien NAYRAT

http://dalibo.com - http://dalibo.org