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From Kirk Pepperdine <kirk.pepperd...@gmail.com>
Subject Re: Feedback and question re Java memory/GC settings for Jmeter load generator CPU issue
Date Mon, 19 Mar 2018 05:39:07 GMT
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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