From: Tom Lane <tgl@sss.pgh.pa.us>
To: =?utf-8?Q?Felix_Geisend=C3=B6rfer?= <felix@felixge.de>
cc: pgsql-performance@postgresql.org
Subject: Re: 10x faster sort performance on Skylake CPU vs Ivy Bridge
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Comments: In-reply-to =?utf-8?Q?Felix_Geisend=C3=B6rfer?= <felix@felixge.de>
	message dated "Fri, 25 Aug 2017 16:12:26 +0200"
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Date: Fri, 25 Aug 2017 11:07:21 -0400
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=3D?utf-8?Q?Felix_Geisend=3DC3=3DB6rfer?=3D <felix@felixge.de> writes:
> I recently came across a performance difference between two machines that=
 surprised me:
> ...
> As you can see, Machine A spends 5889ms on the Sort Node vs 609ms on Mach=
ine B when looking at the "Exclusive" time with explain.depesz.com [3][4]. =
I.e. Machine B is ~10x faster at sorting than Machine B (for this particula=
r query).

I doubt this is a hardware issue, it's more likely that you're comparing
apples and oranges.  The first theory that springs to mind is that the
sort keys are strings and you're using C locale on the faster machine but
some non-C locale on the slower.  strcoll() is pretty darn expensive
compared to strcmp() :-(

			regards, tom lane


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