Re: 2 x quad core or 4 x dual core? - server sizing

On 01/11/2011 11:12 AM, Rafa Griman wrote:
> Hi :)
>
> On Tue, Jan 11, 2011 at 10:56 AM, Martin Berg <[email protected]> wrote:
>   
>> I've thought of this - but only one of my customers have tried this and it
>> did not perform as
>> expected (each core not being as fast as cores from the quad cores).
>> The performance was so bad that they scrapped the server.
>> I didn't have an opportunity to examine this (the problem might not have
>> anything to do
>> with the CPU's) - and I'm just being cautious.
>>     
>
> Could be a problem due to CPU-Memory bandwidth. The "problem" with
> having many cores is that the bandwidth per core decreases as you
> increase the number of cores per socket so apps that require a big
> CPU-memory bandwidth will be affected.
>
> Depending on the DB, you can hit this issue. In the cases in which you
> hit this issue, you can deactivate some cores at the BIOS. Usually
> helps. Another options is to pin certain processes to certain cores
> (cpusets, ...) leaving some other cores free for the OS and whatever
> it has to do (logs, network, ...).
>
> Summarizing: having many cores/sockets is not always good ;) Depends
> on your app, workflow, ...
>
> HTH
>
>    Rafa
>   

This was an only-Oracle Database server, so leaving certain cores for
other activities
would probably not help a lot - and the whole idea of having as many
cores as can be
fitted into the Oracle license is somewhat negated by disabling some of
the cores;-)
Following this line of thought: some years ago I visited a customer that
had just bought a
16-CPU SUN (> $2M) to run their non-Oracle database after having spend 2
years in not
getting sufficient performance on an Intel server.
They had not seen the performance improvements as they expected and
after further
investigation the database vendor came back and adviced to disable of
some of the CPU's.
The customer became so frustrated that they threw the previous database
out and tried
Oracle instead (which worked).

And: sticking certain processes to certain cores requires an OS (hint,
hint ... :-)

Anyway thanks for the suggestions.

Best regards

Martin Berg

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