Bill Au
CBS Interactive
http://www.apache.org/~billa/oscon2012/
Troubleshooting Slow or Hung Java Applications
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Agenda
»Tools of the Trade»Case Studies
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Tools – Out Of The Box
» jinfo, jmap, jstack, jstat»JConsole, VisualVM
– Monitor CPU usage by using JTop plug-in ($JAVA_HOME/demo/management/JTop)
» java.lang.management– Platform MXBeans: runtime, operating system, class
loading, compilation, garbage collection, memory, thread– Sample code in $JAVA_HOME/demo/management– JDK demo and sample was part of JDK download for
jdk6u31 or older, separate download for u32+
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Tools – java.lang.management
»Sample code:import java.lang.management.*;
ThreadMXBean tb=ManagementFactory.getThreadMXBean();
if (tb.isThreadCpuTimeSupported()) {
long[] tids=tb.getAllThreadIds();
for (long tid : tids) {
System.out.println(“cputime:”+tb.getThreadCpuTime(tid));
System.out.println(“usertime:”+tb.getThreadUserTime(tid));
}
}
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Tools
»Garbage collection log– -Xloggc:<filename>– Timestamp and duration of GC events– Sizes before and after GC events– More options to explore:
− -XX:+PrintGCDateStamps− -XX:+PrintGCDetails − -XX:+PrintTenuringDistribution− -XX:+PrintGCApplicationsStoppedTime
– Some GC flags can be set dynamically by jinfo/JConsole/VisualVM: PrintGC, PrintGCDetails, PrintGCTimeStamps
»visualgc – GUI for garbage collection monitoring
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Tools
»Thread dump– kill -3 (or kill –SIGHUP)– JConsole, VisualVM– ThreadMXBean– jstack (-F)
»Consecutive thread dumps– Stop motion animation
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Hung or Slow App
»Long GC pauses and/or high GC overhead– Basic GC tuning
−max heap size: -Xmx− type of collector used
− -XX:+UserSerialGC− -XX:+UseParallelGC/-XX:+UseParallelOldGC− -XX:+UseConcMarkSweepGC− -XX:+UnlockExperimentalVMOptions -XX:+UseG1GC (jdk6u14+)
– Advanced GC tuning− young generation size: -Xmn
– Baseline, tune, measure one change at a time
»Demo: HPjmeter – garbage collection analysis (and more…)
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Hung or Slow App
»Deadlock– Take thread dump to run the JVM’s deadlock detector
»Looping Threads– Monitor CPU times of running threads
−ThreadMXBean− JTop plug-in for JConsole/VisualVM
– Inspect stack trace of suspicious threads
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Slow or Hung App
»Blocked threads– Look for blocked threads waiting on the same condition– Identify bottleneck for resource contention– Inspect code for incautious and/or improper synchronization
»Demo: samurai – thread dump analysis tool»Stuck threads
– Look for runnable threads with the same stack trace across consecutive thread dumps
– Some common causes:−Blocking for a network call without specifying connect and/or
read timeout (default may be no timeout)−Long execution time for calls to backend servers
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Links
»Presentation http://www.apache.org/~billa/oscon2012
»HPjmeter https://h20392.www2.hp.com/portal/swdepot/displayProductInfo.do?productNumber=HPJMETER
»samurai http://yusuke.homeip.net/samurai/en/index.html https://github.com/yusuke/samurai
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