Date: Sat, 4 Nov 2017 16:35:59 -0700
From: Peter Geoghegan <pg@bowt.ie>
To: =?utf-8?B?0K7RgNC40Lkg0KHQvtC60L7Qu9C+0LI=?= <funny.falcon@gmail.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>,
	Sokolov Yura <funny.falcon@postgrespro.ru>,
	Claudio Freire <klaussfreire@gmail.com>,
	Alvaro Herrera <alvherre@2ndquadrant.com>,
	Heikki Linnakangas <hlinnaka@iki.fi>,
	PostgreSQL-Dev <pgsql-hackers@postgresql.org>
Subject: Re: Small improvement to compactify_tuples
Message-ID: <20171104233559.GA8580@marmot>
References: <20170515171331.taa44gjbc7p3aaul@alvherre.pgsql>
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 <CAGTBQpbrCqPLTfM10TPb3G+DXwDzv=5zQzhuDs9RJV1LUK0+WA@mail.gmail.com>
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Юрий Соколов <funny.falcon@gmail.com> wrote:
>tps is also reflects changes:
>~17ktps with qsort
>~19ktps with bucket sort
>
>Also vacuum of benchmark's table is also improved:
>~3s with qsort,
>~2.4s with bucket sort

One thing that you have to be careful with when it comes to our qsort
with partially presored inputs is what I like to call "banana skin
effects":

https://postgr.es/m/CAH2-WzkU2xK2dpZ7N8-A1MvuUTTUvhqkfnA+eUtwNwCtgyCJgw@mail.gmail.com

This may have nothing at all to do with your results; I'm just pointing
it out as a possibility.

-- 
Peter Geoghegan


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