Subject: Re: Poor PostgreSQL scaling on Linux 2.6.25-rc5 (vs 2.6.22)
From: Nicholas Miell <nmiell@comcast.net>
To: Cyrus Massoumi <cyrusm@gmx.net>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>, "Molnar, Ingo" <mingo@elte.hu>,
       LKML <linux-kernel@vger.kernel.org>
In-Reply-To: <47D6FAD0.1020608@gmx.net>
References: <200803111749.29143.nickpiggin@yahoo.com.au>
	 <1205269674.12854.16.camel@entropy>  <47D6FAD0.1020608@gmx.net>
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Date: Tue, 11 Mar 2008 16:12:12 -0700
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On Tue, 2008-03-11 at 22:34 +0100, Cyrus Massoumi wrote:
> Nicholas Miell wrote:
>
> > (Also, ignoring MySQL because it's a terrible piece of software at least
> > when regarding it's scalability is a bad idea. It's the M in LAMP, it
> > has a huge user base, and FreeBSD manages to outperform Linux with the
> > same unscalable piece of software.)
> 
> Did you actually see this? 
> http://www.kernel.org/pub/linux/kernel/people/npiggin/sysbench/
> 
> FreeBSD does not outperform Linux, it's actually a bit faster according 
> to Nick's tests.

I am aware of those results, but in the mail I was responding to, Nick
Piggin said the following:

> The problem with MySQL contention means that if the scheduler
> unluckily chooses to deschedule a lock holder, then you can get
> idle time building up on other cores and you can get context switch
> cascades as things all pile up onto this heavily contended lock. As
> such, it means MySQL is not an ideal candidate for looking at
> performance behaviour. I discounted the relatively worse scaling of
> MySQL with 2.6.25-rc (than 2.6.22) as such an effect.

which I interpreted to mean that MySQL performs worse on 2.6.23+ than on
2.6.22 but for some reason this doesn't matter.

-- 
Nicholas Miell <nmiell@comcast.net>

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