Re: NOT IN subquery optimization

From: David Rowley <david(dot)rowley(at)2ndquadrant(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Andres Freund <andres(at)anarazel(dot)de>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>, Richard Guo <riguo(at)pivotal(dot)io>, "Li, Zheng" <zhelli(at)amazon(dot)com>, "Finnerty, Jim" <jfinnert(at)amazon(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: NOT IN subquery optimization
Date: 2019-03-01 22:28:00
Message-ID: CAKJS1f90E9agVZryVyUpbHQbjTt5ExqS2Fsodmt5_A7E_cEyVA@mail.gmail.com
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On Sat, 2 Mar 2019 at 05:44, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
> Andres Freund <andres(at)anarazel(dot)de> writes:
> > I've not checked, but could we please make sure these cases are covered
> > in the regression tests today with a single liner?
>
> I'm not sure if the second one is actually a semantics bug or just a
> misoptimization? But yeah, +1 for putting in some simple tests for
> corner cases right now. Anyone want to propose a specific patch?

The second is just reducing the planner's flexibility to produce a
good plan. The first is a bug. Proposed regression test attached.

--
David Rowley http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services

Attachment Content-Type Size
not_in_empty_subquery_test.sql text/plain 1.5 KB

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