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 [cid:image005.jpg@01D3BF87.6FA2B260] [cid:image006.jpg@01D3BF87.6FA2B260] [cid:image009.jpg@01D3BF87.6FA2B260]
