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From: Mark Kirkwood <mark.kirkwood@catalyst.net.nz>
To: Josh Berkus <josh@agliodbs.com>
Cc: postgres performance list <pgsql-performance@postgresql.org>
Subject: Re: High CPU usage / load average after upgrading to Ubuntu 12.04
Date: Wed, 20 Feb 2013 12:17:22 +1300
Message-ID: <51240802.2090006@catalyst.net.nz> (raw)
In-Reply-To: <5123BB94.7030603@agliodbs.com>
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On 20/02/13 06:51, Josh Berkus wrote:
> On 02/18/2013 08:28 PM, Mark Kirkwood wrote:
>> Might be worth looking at your vm.dirty_ratio, vm.dirty_background_ratio
>> and friends settings. We managed to choke up a system with 16x SSD by
>> leaving them at their defaults...
> Yeah?  Any settings you'd recommend specifically?  What did you use on
> the SSD system?
>

We set:

vm.dirty_background_ratio = 0
vm.dirty_background_bytes = 1073741824
vm.dirty_ratio = 0
vm.dirty_bytes = 2147483648

i.e 1G for dirty_background and 2G for dirty. We didn't spend much time 
afterwards fiddling with the size much. I'm guessing the we could have 
made it bigger - however the SSD were happier to be constantly writing a 
few G than being handed (say) 50G of buffers to write at once . The 
system has 512G of ram and 32 cores (no hyperthreading).

regards

Mark


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