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From: alexandre - aldeia digital <adaldeia@gmail.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Adding more memory = hugh cpu load
Date: Tue, 11 Oct 2011 08:54:42 -0300
Message-ID: <4E942E82.9010307@gmail.com> (raw)
In-Reply-To: <CAGTBQpaOOu_ADrD7h9Cn_EazPrz4=QQj+jTePyHGEvt7BjJi3g@mail.gmail.com>
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Em 10-10-2011 23:19, Claudio Freire escreveu:
> On Tue, Oct 11, 2011 at 12:02 AM, Samuel Gendler
> <sgendler@ideasculptor.com>  wrote:
>> The original question doesn't actually say that performance has gone down,
>> only that cpu utilization has gone up. Presumably, with lots more RAM, it is
>> blocking on I/O a lot less, so it isn't necessarily surprising that CPU
>> utilization has gone up.  The only problem would be if db performance has
>> gotten worse. Maybe I missed a message where that was covered?  I don't see
>> it in the original query to the list.
>
> Load average (which is presumably the metric in question) includes
> both processes using the CPU and processes waiting for I/O.
> So it *would* be strange for load average to go up like that, if
> database configuration remains the same (ie: equal query plans)

Yep, that's the point. Iostat and vmstat reports a very low use of the 
disks (lower than before the changes are made - perhaps because the cache).
Nothing changed in database itself.



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