invited netflix talk: JVM issues in the age of scale! We take an under the hood look at java locking, memory model, overheads, serialization, uuid, gc tuning, CMS, ParallelGC, java.

1. JVM goes BigData srisatish.ambati AT gmail.com DataStax/OpenJDK 2/28/2011 @srisatish

8. java.util.concurrent also holds locks!

9. Tomcat under concurrent load!

12. yourkit: memory profile

15. ser+deser smaller is better https://github.com/eishay/jvm-serializers.git

21. ------------------------------------------------------------------------------------------------------------------------------- PerfTop: 1485 irqs/sec kernel:18.6% exact: 0.0% [1000Hz cycles], (all, 8 CPUs) ------------------------------------------------------------------------------------------------------------------------------- samples pcnt function DSO _______ _____ ________________________________________________________________ 1882.00 26.3% intel_idle [kernel.kallsyms] 1678.00 23.5% os::javaTimeMillis() libjvm.so 382.00 5.3% SpinPause libjvm.so 335.00 4.7% Timer::ImplTimerCallbackProc() libvcllx.so 291.00 4.1% gettimeofday /lib/libc-2.12.1.so 268.00 3.7% hpet_next_event [kernel.kallsyms] 254.00 3.6% ParallelTaskTerminator::offer_termination(TerminatorTerminator*) libjvm.so ------------------------------------------------------------------------------------------------------------------------------- PerfTop: 1656 irqs/sec kernel:59.5% exact: 0.0% [1000Hz cycles], (all, 8 CPUs) ------------------------------------------------------------------------------------------------------------------------------- samples pcnt function DSO _______ _____ ________________________________________________________________ 6980.00 38.5% sha_transform [kernel.kallsyms] 2119.00 11.7% intel_idle [kernel.kallsyms] 1382.00 7.6% mix_pool_bytes_extract [kernel.kallsyms] 437.00 2.4% i8042_interrupt [kernel.kallsyms] 416.00 2.3% hpet_next_event [kernel.kallsyms] 390.00 2.2% extract_buf [kernel.kallsyms] 376.00 2.1% ThreadInVMfromNative::~ThreadInVMfromNative() libjvm.so 321.00 1.8% T.3542 libjvm.so 298.00 1.6% __ticket_spin_lock [kernel.kallsyms] 296.00 1.6% Timer::ImplTimerCallbackProc() libvcllx.so 255.00 1.4% Unsafe_GetInt libjvm.so

27. Three free parameters Allocation Rate: your workload! Size: defines runway! Live Set, memory Pause times: Stoppages!

28. Four free parameters Allocation Rate: your application load! Size: defines runway! Live Set, system memory Pause times: Stoppages! (fourth: Overheads of GC – Space & CPU.)

32. ... 995.330: [CMS-concurrent-mark: 0.952/1.102 secs] [Times: user=3.69 sys=0.54, real=1.10 secs] 995.330: [CMS-concurrent-preclean-start] 995.618: [CMS-concurrent-preclean: 0.279/0.287 secs] [Times: user=0.90 sys=0.20, real=0.29 secs] 995.618: [CMS-concurrent-abortable-preclean-start] 995.695: [GC 995.695: [ParNew (promotion failed) Desired survivor size 41943040 bytes, new threshold 1 (max 1) - age 1: 29826872 bytes, 29826872 total : 720596K->703760K(737280K), 0.4710410 secs]996.166: [CMS996.317: [CMS-concurrent-abortable-preclean: 0.218/0.699 secs] [Times: user=1.39 sys=0.10, real=0.70 secs] (concurrent mode failure): 4100132K->784070K(5341184K), 4.7478300 secs] 4780154K->784070K(6078464K), [CMS Perm : 17033K->17014K(28400K)], 5.2191410 secs] [Times: user=5.70 sys=0.01, real=5.22 secs] ...

35. Did someone ask about defaults? if (FLAG_IS_DEFAULT(ParallelGCThreads)) { assert(ParallelGCThreads == 0, &quot;Default ParallelGCThreads is not 0&quot;); // For very large machines, there are diminishing returns // for large numbers of worker threads. Instead of // hogging the whole system, use a fraction of the workers for every // processor after the first 8. For example, on a 72 cpu machine // and a chosen fraction of 5/8 // use 8 + (72 - 8) * (5/8) == 48 worker threads. unsigned int ncpus = (unsigned int) os::active_processor_count(); return (ncpus <= switch_pt) ? ncpus : (switch_pt + ((ncpus - switch_pt) * num) / den); } else { return ParallelGCThreads; }

38. JRockit Mission Control

41. GCSpy