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From: Richard Guo <guofenglinux@gmail.com>
Date: Wed, 25 Dec 2024 17:14:53 +0900
Message-ID: <CAMbWs4_wMCPZqRyTyTYc4R+2JMW6ozL-mnRwTMkVmee0jQPL3Q@mail.gmail.com>
Subject: Re: ERROR: corrupt MVNDistinct entry
To: Andrei Lepikhov <lepihov@gmail.com>
Cc: PostgreSQL-development <pgsql-hackers@postgresql.org>
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On Wed, Dec 25, 2024 at 11:34=E2=80=AFAM Andrei Lepikhov <lepihov@gmail.com=
> wrote:
> I have a couple of notes.
> 1. The nulling_relids provides us sensible information about possible
> nulls inside the input. We are not using it to estimate the number of
> such nulls for now. Does Your idea consist of obtaining 'clear'
> statistics and reusing nulling_relids knowledge somewhere later?

Are you referring to the nullfrac estimates?  A RelOptInfo's
nulling_relids records all above outer joins that can null this rel.
However, I cannot see how it helps with nullfrac.

> 2. It is ok for Vars. But what about expressions? We use equal() in
> distinct, MCV and dependencies modules. Do we need to remove nulls
> before using extended statistics as a general rule?

AFAIU, the expressions in extended statistics are not decorated with
any nullingrels bits, are they?

Thanks
Richard