Date: Wed, 17 Aug 2022 10:32:55 -0400
From: Bruce Momjian <bruce@momjian.us>
To: stefan.keller@ost.ch, pgsql-docs@lists.postgresql.org
Cc: Tomas Vondra <tomas.vondra@enterprisedb.com>
Subject: Re: Empty values of  pg_stats_ext when table is empty
Message-ID: <Yvz8F7z+u9Fuxg4P@momjian.us>
References: <163577298184.680.6561061840343770915@wrigleys.postgresql.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <163577298184.680.6561061840343770915@wrigleys.postgresql.org>
Archived-At: 
 <https://www.postgresql.org/message-id/Yvz8F7z%2Bu9Fuxg4P%40momjian.us>
Precedence: bulk

On Mon, Nov  1, 2021 at 01:23:01PM +0000, PG Doc comments form wrote:
> The following documentation comment has been logged on the website:
> 
> Page: https://www.postgresql.org/docs/14/view-pg-stats-ext.html
> Description:
> 
> When table mytable is being inherited it may not contain any data but still
> return row sets from the inheriting tables. Now doing CREATE STATISTICS on
> mytable will work but won't have any values.
> 
> This is very difficult to realize from a user's perspective and can be
> either considered a feature or a bug, i.e. being enhanced.
> 
> Given this is considered as a feature, I suggest to add a comment at the end
> of this documentation
> https://www.postgresql.org/docs/current/view-pg-stats-ext.html like this:
> 
> <<
> Note then there are no values when the table is empty which happens when
> there are tables which inherit from it.
> <<
> 
> I could also think of a run-time warning?

I talked to Tomas Vondra and he says there will be proper parent
statistics in PG 15, due to be released in the next 1-2 months.  Here is
the PG 15 release note item:

	https://www.postgresql.org/docs/15/release-15.html

	Allow extended statistics to record statistics for a parent with all its
	children (Tomas Vondra, Justin Pryzby)

	Regular statistics already tracked parent and parent/all-children
	statistics separately.

-- 
  Bruce Momjian  <bruce@momjian.us>        https://momjian.us
  EDB                                      https://enterprisedb.com

  Indecision is a decision.  Inaction is an action.  Mark Batterson