Re: Removing unneeded self joins

From: Andrei Lepikhov <a(dot)lepikhov(at)postgrespro(dot)ru>
To: Alexander Korotkov <aekorotkov(at)gmail(dot)com>, Alexander Lakhin <exclusion(at)gmail(dot)com>, Richard Guo <guofenglinux(at)gmail(dot)com>
Cc: "Gregory Stark (as CFM)" <stark(dot)cfm(at)gmail(dot)com>, Michał Kłeczek <michal(at)kleczek(dot)org>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>
Subject: Re: Removing unneeded self joins
Date: 2024-05-02 09:44:54
Views: Raw Message | Whole Thread | Download mbox | Resend email
Lists: pgsql-hackers

On 5/1/24 18:59, Alexander Korotkov wrote:
> I think we probably could forbid SJE for the tables with TABLESAMPLE
> altogether. Please, check the attached patch.
Your patch looks good to me. I added some comments and test case into
the join.sql.

One question for me is: Do we anticipate other lateral self-references
except the TABLESAMPLE case? Looking into the extract_lateral_references
implementation, I see the only RTE_SUBQUERY case to be afraid of. But we
pull up subqueries before extracting lateral references. So, if we have
a reference to a subquery, it means we will not flatten this subquery
and don't execute SJE. Do we need more code, as you have written in the
first patch?

Andrei Lepikhov
Postgres Professional

Attachment Content-Type Size
0001-Forbid-self-join-elimination-on-table-sampling-scans.patch text/x-patch 3.7 KB

In response to


Browse pgsql-hackers by date

  From Date Subject
Next Message Alexander Korotkov 2024-05-02 10:07:54 Re: Removing unneeded self joins
Previous Message Yugo NAGATA 2024-05-02 09:00:27 Re: Extend ALTER DEFAULT PRIVILEGES for large objects