Date: Sun, 12 Dec 2021 11:52:56 -0600
From: Justin Pryzby <pryzby@telsasoft.com>
To: Tomas Vondra <tomas.vondra@enterprisedb.com>
Cc: Zhihong Yu <zyu@yugabyte.com>,
	Jaime Casanova <jcasanov@systemguards.com.ec>,
	pgsql-hackers@postgresql.org
Subject: Re: extended stats on partitioned tables
Message-ID: <20211212175255.GO17618@telsasoft.com>
References: <20210925223152.GA7877@telsasoft.com>
 <20210926202550.GA831@telsasoft.com>
 <20211007202646.GA9522@ahch-to>
 <20211007224543.GH27491@telsasoft.com>
 <46f37069-55cb-db6a-a15a-e351a2606592@enterprisedb.com>
 <20211103231904.GP17618@telsasoft.com>
 <689accb1-76e8-5115-6ed0-336749cdca57@enterprisedb.com>
 <20211203052411.GU17618@telsasoft.com>
 <CALNJ-vQSpBxw-gjZ--p-vo_yr2yHaXXOn_g8i=DQam_aAW3GwQ@mail.gmail.com>
 <8052505e-2dd2-e8cb-26c9-cbb5dff7d750@enterprisedb.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <8052505e-2dd2-e8cb-26c9-cbb5dff7d750@enterprisedb.com>
User-Agent: Mutt/1.9.4 (2018-02-28)
Archived-At: 
 <https://www.postgresql.org/message-id/20211212175255.GO17618%40telsasoft.com>
Precedence: bulk

+          * XXX Can't we simply look at rte->inh?
+          */
+         inh = root->append_rel_array == NULL ? false :
+                 root->append_rel_array[onerel->relid]->parent_relid != 0;

I think so.  That's what I came up with while trying to figured this out, and
it's no great surprise that it needed to be cleaned up - thanks.

In your 0003 patch, the "if inh: break" isn't removed from examine_variable(),
but the corresponding thing is removed everywhere else.

In 0003, mcv_clauselist_selectivity still uses simple_rte_array rather than
rt_fetch.

The regression tests changed as a result of not populating stx_data; I think
it's may be better to update like this:

SELECT stxname, stxdndistinct, stxddependencies, stxdmcv, stxoid IS NULL
  FROM pg_statistic_ext s LEFT JOIN pg_statistic_ext_data d
  ON d.stxoid = s.oid
  WHERE s.stxname = 'ab1_a_b_stats';

There's this part about documentation for the changes in backbranches:

On Sun, Sep 26, 2021 at 03:25:50PM -0500, Justin Pryzby wrote:
> Also, I think in backbranches we should document what's being stored in
> pg_statistic_ext, since it's pretty unintuitive:
>  - noninherted stats (FROM ONLY) for inheritence parents;
>  - inherted stats (FROM *) for partitioned tables;

spellcheck: inheritence should be inheritance.

All for now.  I'm going to update the regression tests for dependencies and the
other code paths.

-- 
Justin