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From Antony Bowesman <Antony.Bowes...@williamhill.com.au>
Subject RE: Feedback and question re Java memory/GC settings for Jmeter load generator CPU issue
Date Mon, 19 Mar 2018 21:53:19 GMT
Mmm, I saw the images had gone too :(

I have set up to do a gc log next time I run the test and will dig into it. I've been using
the default Java8 GC, which is Parallel, so I am going to use CMS to see if that makes a difference.
I gather it is supposed to favour shorter pauses, so I'll see what happens and post back results.

Cheers
Antony


> -----Original Message-----
> From: Kirk Pepperdine [mailto:kirk.pepperdine@gmail.com]
> Sent: Monday, 19 March 2018 4:39 PM
> To: JMeter Users List <user@jmeter.apache.org>
> Subject: Re: Feedback and question re Java memory/GC settings for Jmeter
> load generator CPU issue
> 
> Hi,
> 
> The images seem to have been filter out of my email at least.
> 
> Can you collect and post a GC log. Most likely young gen is too small but a gc
> log would confirm this.
> 
> Kind regards,
> Kirk
> 
> > On Mar 19, 2018, at 3:37 AM, Antony Bowesman
> <Antony.Bowesman@williamhill.com.au> wrote:
> >
> > Hi,
> >
> > I just thought I’d send in some info about a problem I’ve been looking at
> recently – with a question of best GC settings
> >
> > I have a number of JMeter load generators (LG) and I have been seeing
> CPU spikes on the boxes during a test. I am monitoring CPU and memory
> from within a Java sampler, so have the following charts
> >
> > 1.       First chart shows the request/sec rate (RHS axis) in blue and the CPU
> max % in yellow (sampled every 5s). The blue vertical lines indicate a drop in
> request rate (as recorded by the request finishing and therefore being
> logged) an a corresponding spike to ‘catch up’. I note that the spikes always
> correspond to a spike in CPU.
> > 2.       The second shows the spikes appearing to correlate with the increase
> in committed memory
> > 3.       The third is after the JVM setting change. Note the behaviour still
> occurs in CPU/request rate with a CPU spike in the green circle, but not until
> the later stages. (NB: CPU scale is CPU% * 200 to fit on the graph)
> >
> > This behaviour is the same across all the LGs and happens regardless of the
> way the target hosts are reached across the network, so I believe it’s a
> JVM/host issue.
> >
> > The original memory settings were
> >
> > -Xms1G -Xmx12G -XX:NewSize=1024m -XX:MaxNewSize=4096m
> >
> > But I changed –Xms12G so that all memory is allocated initially and that
> makes a huge change to the behaviour.
> >
> > However, I still see the CPU spike. Has anyone got some optimum GC
> settings they have used that can avoid this?
> >
> > Thanks
> > Antony
> >
> >
> >
> >
> >
> >
> >


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