Message-ID: <539B22BD.6010803@optionshouse.com>
Date: Fri, 13 Jun 2014 11:11:41 -0500
From: Shaun Thomas <sthomas@optionshouse.com>
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To: Tim Kane <tim.kane@gmail.com>, Brio <brianoraas@gmail.com>,
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Subject: Re: postgres files in use not staying in linux file cache
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On 06/13/2014 02:19 AM, Tim Kane wrote:

> I ask because I’ve just read your statement above about 3.2 being
> pants-on-head, and having had more luck with 3.8 and above – despite
>  most installations being on much older (2.6.19) kernels (as per the
> thread).

Well, the issue is that the 3.2 kernel was a huge departure from the 2.6 
tree that most people are still using. Thanks to RHEL, CentOS and their 
ilk, the 2.6 tree has had a much longer lifetime than it probably should 
have. As a result, the newer kernels haven't had sufficient real-world 
server testing.

With 3.2 being the first of those, it was a bit wonky, to be honest. The 
new CPU scheduler didn't have enough knobs, and the knobs that *were* 
there, were set more appropriately for desktop use. The memory manager 
was a train wreck and has been patched numerous times with rather 
sweeping changes since. For a while, there was even a bug at how system 
load was calculated that caused it to be off by an order of magnitude or 
more based on process switching activity.

The overall situation has improved significantly, as has the development 
momentum. It's extremely difficult to say which kernel versions have 
more risk than others, since no kernel seems to be around for more than 
a month or two before the next one comes out. My opinion has been to get 
on the latest stable kernel for the distribution, and ignore everything 
else.

For Ubuntu 12.04.4 LTS, that's 3.11.

Our systems are definitely much happier since the upgrade, but the 
plural of anecdote is not data. :)

-- 
Shaun Thomas
OptionsHouse, LLC | 141 W. Jackson Blvd. | Suite 800 | Chicago IL, 60604
312-676-8870
sthomas@optionshouse.com

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