From: Shaun Thomas <sthomas@optionshouse.com>
To: Craig James <cjames@emolecules.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Hyperthreading (was: Two identical systems, radically different performance)
Date: Wed, 10 Oct 2012 07:52:37 -0500
Message-ID: <50756F95.7040006@optionshouse.com> (raw)
In-Reply-To: <CAFwQ8re9O2Nvao3UsUxDxFZZUsoSqNJSC4jaKGB9cJ7_YyjoBA@mail.gmail.com>
References: <CAFwQ8revW5Ez6uCUqPeUFVHh0pdy0OZKv8_nM0SvxHgTM055EQ@mail.gmail.com>
<CAFwQ8re9O2Nvao3UsUxDxFZZUsoSqNJSC4jaKGB9cJ7_YyjoBA@mail.gmail.com>
On 10/09/2012 06:30 PM, Craig James wrote:
> ra:8192 walb:1M ra:256 walb:1M ra:256 walb:256kB
> ---------------- ---------------- -----------------
> -c -t Run1 Run2 Run3 Run4 Run5 Run6 Run7 Run8 Run9
> 40 2500 4261 3722 4243 9286 9240 5712 9310 8530 8872
> 50 2000 4138 4399 3865 9213 9351 9578 8011 7651 8362
I think I speak for more than a few people here when I say: wat.
About the only thing I can ask, is: did you make these tests fair? And
by fair, I mean:
echo 3 > /proc/sys/vm/drop_caches
pg_ctl -D /your/pg/dir restart
Between every test to make sure shared buffers and the OS inode cache
was empty before the start of each test? If you're using that bash-style
for-loop you attached earlier, probably not. Still though, I don't think
that would account for this much variance between having read-ahead at
8M as opposed to 256kb.
My head hurts.
--
Shaun Thomas
OptionsHouse | 141 W. Jackson Blvd. | Suite 500 | Chicago IL, 60604
312-444-8534
sthomas@optionshouse.com
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To: pgsql-performance@postgresql.org
Cc: sthomas@optionshouse.com, cjames@emolecules.com
Subject: Re: Hyperthreading (was: Two identical systems, radically different performance)
In-Reply-To: <50756F95.7040006@optionshouse.com>
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