Re: Optimize join selectivity estimation by not reading MCV stats for unique join attributes

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Tomas Vondra <tomas(dot)vondra(at)enterprisedb(dot)com>
Cc: David Geier <geidav(dot)pg(at)gmail(dot)com>, Richard Guo <guofenglinux(at)gmail(dot)com>, PostgreSQL Developers <pgsql-hackers(at)lists(dot)postgresql(dot)org>
Subject: Re: Optimize join selectivity estimation by not reading MCV stats for unique join attributes
Date: 2022-11-18 14:45:44
Message-ID: 2185327.1668782744@sss.pgh.pa.us
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Tomas Vondra <tomas(dot)vondra(at)enterprisedb(dot)com> writes:
> On 11/18/22 09:54, David Geier wrote:
>> I couldn't come up with any reasonable way of writing an automated test
>> for that.

> I don't think you can write a test for this, because there is no change
> to behavior that can be observed by the user.

Yeah, and the delta in performance is surely too small to be
measured reliably in the buildfarm. I think coverage will have
to be sufficient.

regards, tom lane

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