Message-ID: <4E94A828.1040201@tweakers.net>
Date: Tue, 11 Oct 2011 22:33:44 +0200
From: Arjen van der Meijden <acmmailing@tweakers.net>
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To: pgsql-performance@postgresql.org
Subject: Re: Adding more memory = hugh cpu load [solved]
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On 11-10-2011 20:05 Claudio Freire wrote:
> On Tue, Oct 11, 2011 at 3:02 PM, alexandre - aldeia digital
> <adaldeia@gmail.com>  wrote:
>> 2) Change all memory chips to new others, instead of maintain the old (16
>> GB) + new (32 GB).
>
> Of course, mixing disables double/triple/whatuple channel, and makes
> your memory subsystem correspondingly slower.
> By a lot.
>

That really depends on the chipset/server. The current intel E56xx-chips 
(and previous E55xx) basically just expect groups of 3 modules per 
processor, but it doesn't really matter whether that's 3x2+3x4 or 6x4 in 
terms of performance (unless the linuxkernel does some weirdness of 
course). It at least won't disable triple-channel, just because you 
added different size modules. Only when you get to too many 'ranks', 
you'll see performance degradation. But that's in terms of clock speed, 
not in disabling triple channel.

But as said, that all depends on the memory controller in the server's 
mainboard or processors.

Best regards,

Arjen