Javaday2010 - Jvm Power Tools - What is my JVM doing?

Managing & Tuning JDK monitoring & management power tools: what is my Java Virtual Machine doing? Carlo Bonamico - NIS s.r.l. / JUG Genova carlo.bonamico@nispro.it Carlo Bonamico - carlo.bonamico@nispro.it - JUG Genova Javaday IV – Roma – 30 gennaio 2010

We are so used to Java... ● That we often forget what's required behind the scenes to give us  robustness and security  platform independence – linux/windows/solaris/you name it... – 32/64 bit  performance – with significant increases at every JVM release (think 1.6 vs 1.5) – benefit to existing code with NO changes  manageability  rich APIs and commercial/open source ecosystem ● But it is interesting (and sometimes necessary) to get a deeper look at what's happening behind the scenes... Carlo Bonamico - carlo.bonamico@nispro.it - JUG Genova Javaday IV – Roma – 30 gennaio 2010

The good news ● is that the JVM lets us (almost) forget about memory management, code compilation and optimization ● The better news is that it also gives us powerful tools to  monitor  debug  tune  troubleshoot ● Its internal mechanisms  including the Garbage Collector and dynamic Just in Time compiler Carlo Bonamico - carlo.bonamico@nispro.it - JUG Genova Javaday IV – Roma – 30 gennaio 2010

We will learn how to... ● find active JVMs with jps ● anaylze memory consumption and garbage collection behavior with jstat ● get an overview of VM activities with jconsole ● analyze in depth VM behavior with VisualVM identifying  local and remote Virtual Machines  performance bottlenecks with VisualVM's profiler  threading issues with the Thread Dump Analyzer  causes of OutOfMemory errors and PermGen errors ● detect memory leaks ● trace and debug running applications in production with btrace Carlo Bonamico - carlo.bonamico@nispro.it - JUG Genova Javaday IV – Roma – 30 gennaio 2010

Finding the right VM with jps ● List all java processes ● jps  including command line parameters and properties ● jps lvm ● 29760 sun.tools.jps.Jps lvm Dapplication.home=/usr/lib/jvm/java6 sun1.6.0.16 Xms8m ● 4752 org.codehaus.classworlds.Launcher "cli:executephase" Xmx768m Dclassworlds.conf=/home/charlieb/build/apachemaven 2.2.1/bin/m2.conf Dmaven.home=/home/charlieb/build/apachemaven 2.2.1  on a remote machine (requires jstatd running on the server) ● jps lvm server Carlo Bonamico - carlo.bonamico@nispro.it - JUG Genova Javaday IV – Roma – 30 gennaio 2010

jstat ● To enable remote access to a machine stats ● jstatd Djava.security.policy=jstatd.policy  which contains ● grant codebase "file:${java.home}/../lib/tools.jar" { ● permission java.security.AllPermission; ● }; ● ● Carlo Bonamico - carlo.bonamico@nispro.it - JUG Genova Javaday IV – Roma – 30 gennaio 2010

Efficient Garbage Collection ● Almost nobody does reference counting today :-)  When your JVM is using a few GBs of memory, it cannot check all objects all the time ● So you need a smart way of separating objects that are likely to be collected from the ones in use  generations: objects that have been created recently are more likely to be collected soon – think of request attributes  objects that have been there for a long time are unlikely to be collected – think of Spring services, EJBs, singletons Carlo Bonamico - carlo.bonamico@nispro.it - JUG Genova Javaday IV – Roma – 30 gennaio 2010

Generational Collection in the JVM ● Heap space split into  Eden – Young objects  Survivor 1/2 – Older objects  Old ● Perm(anent)Gen(eration) area for objects that will not be deallocated until the end  class and method objects Carlo Bonamico - carlo.bonamico@nispro.it - JUG Genova Javaday IV – Roma – 30 gennaio 2010

Start with an OOM / Permgen ● OutOfMemoryError  but increasing -Xmx will not help... ● Then it might be a PermGen space saturation  increase -XX:MaxPermSize=256m  find and detect classloading issues Carlo Bonamico - carlo.bonamico@nispro.it - JUG Genova Javaday IV – Roma – 30 gennaio 2010

Monitoring with jstat ● Command line tool for accessing GC and JIT stats ● jstat gcutil <vmid> <interval> ● jstat gcutil 21891 250  refresh every 250 ms ● S0 S1 E O P YGC YGCT FGC FGCT GCT ● 12.44 0.00 27.20 9.49 96.70 78 0.176 5 0.495 0.672 ● 12.44 0.00 62.16 9.49 96.70 78 0.176 5 0.495 0.672 GC ● 12.44 0.00 83.97 9.49 96.70 78 0.176 5 0.495 0.672 ● 0.00 7.74 0.00 9.51 96.70 79 0.177 5 0.495 0.673 ● 0.00 7.74 23.37 9.51 96.70 79 0.177 5 0.495 0.673 ● 0.00 7.74 43.82 9.51 96.70 79 0.177 5 0.495 0.673 ● 0.00 7.74 58.11 9.51 96.71 79 0.177 5 0.495 0.673  S0/S1 = survivor spaces, E = Eden, O = Old, P = Permanent  All values are % of available space Carlo Bonamico - carlo.bonamico@nispro.it - JUG Genova Javaday IV – Roma – 30 gennaio 2010

JVM Overview with jconsole ● Included since JDK 1.5  memory analysis  CPU load  Classloading stats  Thread stats  Classpath  JMX console  (and more...) Carlo Bonamico - carlo.bonamico@nispro.it - JUG Genova Javaday IV – Roma – 30 gennaio 2010

Classpath, launch arguments and properties Carlo Bonamico - carlo.bonamico@nispro.it - JUG Genova Javaday IV – Roma – 30 gennaio 2010

Incremental GC as seen by jconsole Carlo Bonamico - carlo.bonamico@nispro.it - JUG Genova Javaday IV – Roma – 30 gennaio 2010

In-depth with (j)visualvm ● Even more powerful than jconsole  Included in the JDK since 1.6.0_07 ● Supports  local VMs through the JVMPI interface – the same used by any IDE for debug  remote VMs through – jstatd – direct JMX over RMI connection Carlo Bonamico - carlo.bonamico@nispro.it - JUG Genova Javaday IV – Roma – 30 gennaio 2010

Thread Monitoring and Dump Carlo Bonamico - carlo.bonamico@nispro.it - JUG Genova Javaday IV – Roma – 30 gennaio 2010

Memory analysis Carlo Bonamico - carlo.bonamico@nispro.it - JUG Genova Javaday IV – Roma – 30 gennaio 2010

And more... ● CPU/Memory profiler  subset of NetBeans profiler  new sampling profiler since version 1.2.1 Carlo Bonamico - carlo.bonamico@nispro.it - JUG Genova Javaday IV – Roma – 30 gennaio 2010

BTrace ● B(ytecode)Trace  conceptually similar to Solaris DTrace  can be used on any Java platform/app. ● Dynamically connects to a running Java application  and attach short “scripts” which log a range of events and infos such as – method calls – execution times – constructor invocation – available memory Carlo Bonamico - carlo.bonamico@nispro.it - JUG Genova Javaday IV – Roma – 30 gennaio 2010

Btrace scripts ● Script execution is tied to several situations  reaching a specific line number  invoking a given method – identified by signature or annotation  returning from a method  invoking system calls (e.g. exit)  recurring timer ● In a way, BTrace scripts are very similar to read-only AOP’s aspects  can be attached to any existing Java code Carlo Bonamico - carlo.bonamico@nispro.it - JUG Genova Javaday IV – Roma – 30 gennaio 2010

Examples ● The scripts are simple Java classes which take advantage of methods from the btrace API  simple but powerful annotations. ● Tracing session creation with hibernate ● @BTrace ● public class HelloWorldTrace { ● ● // probe the openSession() method of Hibernate SessionFactory ● @OnMethod( ● clazz=”org.hibernate.SessionFactory”, ● method=”openSession” ● ) ● public static void onOpenSessionTrace() { ● // you can only log using the stati println method from BTraceUtils ● println(”Hibernate: opening a new session…”); ● } ● } Carlo Bonamico - carlo.bonamico@nispro.it - JUG Genova Javaday IV – Roma – 30 gennaio 2010

Examples: JAX-WS ● Intercepts all calls to methods in classes which are annotated with @WebService and logs execution times ● @OnMethod( ● clazz="@javax.jws.WebService", ● method="@javax.jws.WebMethod" ● ) ● public static void onWebserviceEntry() { – print("entering webservice "); – println(strcat(strcat(name(probeClass()), "."), probeMethod())); – startTime = timeMillis(); ● } ● ● @OnMethod( ● clazz="@javax.jws.WebService", ● method="@javax.jws.WebMethod", ● location=@Location(Kind.RETURN) ● ) ● public static void onWebserviceReturn() { – println(strcat("Time taken (msec) ", str(timeMillis() startTime))); ● } Carlo Bonamico - carlo.bonamico@nispro.it - JUG Genova Javaday IV – Roma – 30 gennaio 2010

Yesterday news ● JDK 1.6.0_18 released last week  includes visualvm 1.2.1  includes NUMA-aware Garbage Collector – Non-Uniform Memory Allocation – takes into account that the cost of accessing RAM is not uniform anymore – 30% more efficient with large memory allocations – linux/solaris only :-) Carlo Bonamico - carlo.bonamico@nispro.it - JUG Genova Javaday IV – Roma – 30 gennaio 2010

References ● VisualVM official site  https://visualvm.dev.java.net ● BTrace  https://btrace.dev.java.net ● Articles on Hotspot  http://java.sun.com/javase/technologies/hotspot/index .jsp Carlo Bonamico - carlo.bonamico@nispro.it - JUG Genova Javaday IV – Roma – 30 gennaio 2010

Thanks for your attention! ● Learn more at  http://www.carlobonamico.com/blog  http://juggenova.net – presentations, demos, code samples ● Meet me at the my company (NIS) booth in the exhibition hall ● Contact me at  carlo.bonamico@gmail.com ● Related reading: Continuous Integration with Hudson  http://www.slideshare.net/carlo.bonamico/continuous-integration-with-hudson Carlo Bonamico - carlo.bonamico@nispro.it - JUG Genova Javaday IV – Roma – 30 gennaio 2010

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Javaday2010 - Jvm Power Tools - What is my JVM doing?

by carlo.bonamico on Jan 30, 2010

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Javaday2010 - Jvm Power Tools - What is my JVM doing? — Presentation Transcript