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 > <[email protected]> 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 > > > > > > >
