Re: cpu comparison

From: Tomas Vondra
Subject: Re: cpu comparison
Date: ,
Msg-id: 4E24AC18.807@fuzzy.cz
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In response to: Re: cpu comparison  ("")
Responses: Re: cpu comparison  ("")
Re: cpu comparison  ("M. D.")
List: pgsql-performance

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cpu comparison  ("M. D.", )
 Re: cpu comparison  ("", )
  Re: cpu comparison  (Tomas Vondra, )
   Re: cpu comparison  ("", )
   Re: cpu comparison  ("M. D.", )
    Re: cpu comparison  (Samuel Gendler, )
 Re: cpu comparison  (Josh Berkus, )
 Re: cpu comparison  (Greg Smith, )
  Re: cpu comparison  (Scott Marlowe, )

Dne 18.7.2011 22:11,  napsal(a):
>> > In my testing I have a 32bit CentOS on the x3450, but a 64bit CentOS
>> > on the E5335.  Can this make such a bit difference or should the
>> > perform fairly close to the same speed?  Both servers have 8GB of
>> > RAM, and the database I tested with is only 3.7GB.
>> >
>> > I'm a bit surprised as the x3450 has DDR3, while the E5335 has DDR2,
>> > and of course because of the cycle speed difference alone I would
>> > think the X3450 should beat the E5335.
>> >
> Yes, you have basically shown that  running two different tests give
> different results -- or that an apple is not an orange. You need to
> only vary 1 variable at a time for it to mean anything.

He just run the same test on two different machines - I'm not sure
what's wrong with it? Sure, it would be nice to compare 32bit to 32bit,
but the OP probably can't do that and wonders if this is the cause. Why
is that comparing apples and oranges?

According to http://www.cpubenchmark.net, the X3450 is about 2x as fast
as E5335 (5,298 vs. 2,575), although this is just a synthetic score.

I'm a bit confused by the E5335 cpuinfo output, because it says "cpu
cores : 1" as I'd expect "4" here.

I do recall hyperthreading generally was not recommended for a DB, not
sure if that changed recently. A quick search revealed this post

http://serverfault.com/questions/219791/hyperthreading-vs-sql-server-postgresql

stating that since Nehalem CPUs (and X3450 is Nehalem) this should not
be a problem anymore. Not sure if it's true, I guess it's worth testing
as it might slow down the X3450 box.

OP: We need more details about the test's has run, without them we're
just guessing. Have you collected some system stats (vmstat, iostat)
during the test?

Tomas


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