Re: Performance improvement for joins where outer side is unique

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: David Rowley <david(dot)rowley(at)2ndquadrant(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Performance improvement for joins where outer side is unique
Date: 2017-01-27 17:15:40
Message-ID: CA+Tgmoa-M=pAQ8fB1eDgSV4n9UCUHJMt2B6MdD9X9LcBbFy0fg@mail.gmail.com
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On Fri, Jan 27, 2017 at 11:44 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> I'm afraid though that we may have to do something about the
> irrelevant-joinquals issue in order for this to be of much real-world
> use for inner joins.

Maybe, but it's certainly not the case that all inner joins are highly
selective. There are plenty of inner joins in real-world applications
where the join product is 10% or 20% or 50% of the size of the larger
input.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

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