On 31/03/2016 5:47 PM, Andrew Rowley wrote:
On 31/03/2016 07:01 PM, David Crayford wrote:
When a stop the world event happens watch those zIIPs spike! I've
been amused watching the RMF zIIP metrics in Grafana.
Which garbage collection option do you use? Have you played around
with different GC options? I have found it can make a big difference.
(For my programs the default gencon seems best. Optthruput was terrible.)
One of the difficulties in figuring out GC is that most of the
information seems to assume the most important thing is trying to
minimize the stopped time, hence multithreading, concurrent GC etc.
Not so helpful if what you really want is to minimize total CPU
consumed e.g. batch on z/OS.
Thanks for the info Andrew. We use the default GC options and our
workloads are both long running agents and batch jobs. I really do want
to learn a lot more about how to tune the JVM for each specific
workload. The SMF 30 records are useless. How do I find out how much
time is spent in JIT overhead compared to actual processing? What tools
do you use to profile your JVM apps?
I wrote an agent to forward RMF and netstat metrics into Grafana and you
can see that when I run a Java batch job it really does take a lot of
zIIP http://users.tpg.com.au/crayford/GrafSpike.PNG. The FTS1 CPU is
running CICS, IMS and that one Java batch job spikes past it. We're an
ISV and the only time we reach full capacity on our machine is when the
testers are running test suites. There is a spike on the zIIP which
looks like GC. Unfortunately RMF metrics are not very granular which is
why the graphs look like tetris blocks! Our sysprog tells me that's RMF
but I would love to get reporting intervals aggregated to 10 second
intervals. Then the spike would be more pronounced and the interval in
the histogram shorter.
--
Andrew Rowley
Black Hill Software
+61 413 302 386
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