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From Felix Schumacher <felix.schumac...@internetallee.de>
Subject RE: Feedback and question re Java memory/GC settings for Jmeter load generator CPU issue
Date Tue, 20 Mar 2018 08:40:38 GMT


Am 19. März 2018 22:53:19 MEZ schrieb Antony Bowesman <Antony.Bowesman@williamhill.com.au>:
>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.

As you have 12gb of heap, you could try to use g1, too.

On the other hand side, this seems to be quite a lot of heap. What are you doing in your test
plan?

And as a nice plus, you could tell us about the used versions for jvm, jmeter and os. 

Regards, 
 Felix 



>
>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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