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From Christopher Schultz <ch...@christopherschultz.net>
Subject Re: Tuning session replication on clusters
Date Thu, 06 Sep 2012 15:36:57 GMT
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Kyle,

On 9/5/12 9:59 PM, kharper2@oreillyauto.com wrote:
> Alright, I did some more testing with another application and found
> the following:
> 
> Sess    Time (sec 10	0.101 125	0.101 500	0.201 1500	0.201 1800
> 0.101 2400	0.101 42,000	0.901  (that's not a typo)

Good to know that Tomcat itself does not seem to be the problem:
thanks for the report.

One question:

> After further research, the problem we're seeing is performance
> with replication when the number of sessions is larger than around
> 2000.  Using Jmeter on our test servers I can reproduce the
> problem.  Here are the times it takes to replicate X number of
> sessions when an application is restarted: Sess   Time (sec) 10
> 0.101 125		 0.401 500		 1.302 1500		 2.104 1800		 5.308 1800
> 6.709 2400		 15.02 3600		 30.285 3600		 27.238
> 
> The times make sense until around 1500.  The time it takes to
> replicate more than 1500 sessions becomes exponentially worse.

Plot those as X-Y in a spreadsheet and you'll see that it's only a bit
worse than linear, especially after 1500. There's no enough data
presented to draw an "exponential performance curve" conclusion:
you're going to need more data to see if this is worse than linear.
Can you collect more data? I know that creating 42k sessions of 700MiB
each is probably a .. challenge, but more data would certainly be helpful.

- -chris
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