Re: 10x faster sort performance on Skylake CPU vs Ivy Bridge

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Felix Geisendörfer <felix(at)felixge(dot)de>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: 10x faster sort performance on Skylake CPU vs Ivy Bridge
Date: 2017-08-25 15:07:21
Message-ID: 793.1503673641@sss.pgh.pa.us
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=?utf-8?Q?Felix_Geisend=C3=B6rfer?= <felix(at)felixge(dot)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 Machine 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 particular 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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