JVM: need for speed

• Bio: Developer, coach, speaker, author
• Company: Aestas/IT (http://aestasit.com)

• E-mail: andrey@aestasit.com
• Linkedin: http://www.linkedin.com/in/andreyadamovich
• Lanyrd: http://lanyrd.com/profile/andrey-adamovich
• GitHub: https://github.com/aadamovich
• SO: http://stackoverflow.com/users/162792/andrey-adamovich
• Twitter: @codingandrey, @aestasit

• Picture is shown
• You guess what the next topic is
• First one to guess gets a sticker!

> java -XX:+PrintFlagsFinal -version | wc -l
java version "1.8.0_45"
Java(TM) SE Runtime Environment (build 1.8.0_45-b15)
Java HotSpot(TM) 64-Bit Server VM (build 25.45-b02, mixed mode)
714

> java -XX:+PrintFlagsFinal -version | wc -l
java version "1.7.0_80"
Java(TM) SE Runtime Environment (build 1.7.0_80-b15)
Java HotSpot(TM) 64-Bit Server VM (build 24.80-b11, mixed mode)
668

> java -XX:+PrintFlagsFinal -version | wc -l
java version "1.6.0_45"
Java(TM) SE Runtime Environment (build 1.6.0_45-b06)
Java HotSpot(TM) 64-Bit Server VM (build 20.45-b01, mixed mode)
670

> java -XX:+PrintFlagsFinal -version | grep GC | wc -l
65

• Web application
• Streaming application
• Background job

-Xms<heap size>[g|m|k] 
-Xmx<heap size>[g|m|k]
-XX:PermSize=<perm gen size>[g|m|k] 
-XX:MaxPermSize=<perm gen size>[g|m|k]
-Xmn<young size>[g|m|k]
-XX:SurvivorRatio=<ratio>

-XX:+UseConcMarkSweepGC 
-XX:+UseCMSInitiatingOccupancyOnly 
-XX:+ScavengeBeforeFullGC 
-XX:+CMSScavengeBeforeRemark
-XX:+CMSConcurrentMTEnabled
-XX:CMSInitiatingOccupancyFraction=70

-XX:+PrintGCDetails 
-XX:+PrintGCDateStamps 
-Xloggc:<file-path> 
-XX:+PrintGCApplicationConcurrentTime 
-XX:+PrintSafepointStatistics 
-XX:+PrintHeapAtGC

On out of memory:

-XX:+HeapDumpOnOutOfMemoryError 
-XX:HeapDumpPath=<path to dump>`date`.hprof

Or manually:

jmap -dump:file=<path to dump> <java process id>

• Object Retained Size
• Object Shallow Size
• Stale Objects (not connected to GC roots)

• YourKit
• jProfiler

• Dead locks
• 100% CPU load
• Hanging I/O

jstack <java process pid>

• Use MBean with name java.lang:type=Threading
• Call getAllThreadIds
• Loop through all retrieved IDs and call getThreadInfo

for ((a=1; a <= 60; a++))
do 
  jstack 7789 > thread-dump.$a
  sleep 1
  echo $a
done

A thread can be in one of the following states:

• NEW A thread that has not yet started is in this state.
• RUNNABLE A thread executing in the Java virtual machine is in this state.
• BLOCKED A thread that is blocked waiting for a monitor lock is in this state.

• WAITING A thread that is waiting indefinitely for another thread to perform a particular action is in this state.
• TIMED_WAITING A thread that is waiting for another thread to perform an action for up to a specified waiting time is in this state.
• TERMINATED A thread that has exited is in this state.

• Non-reproducable issues
• Hard-to-understand code

-agentlib:jdwp=transport=dt_socket,server=y,address=1337

YouDebug is a non-interactive debugger scripted by Groovy to assist remote troubleshooting and data collection to analyze failures.

• http://youdebug.kohsuke.org/
• https://github.com/kohsuke/youdebug

public class SubStringTest {
  public static void main(String[] args) {
    String s = someLengthComputationOfString();
    System.out.println(s.substring(5));
  }
  private static String someLengthComputationOfString() {
    ...;
  }
}

breakpoint("com.acme.SubStringTest",3) {
  println "s="+s;
}

> java -jar youdebug.jar -socket 1337 SubStringMonitor.ydb
s=test

• Lack of support for latest JVM features
• Lack of support for other JVM langauges
• Obfuscation is always an issue

• Memory allocation profiling
• CPU profiling
• Lock profiling

• YourKit
• jProfiler

MH is a Java harness for building, running, and analysing nano/micro/milli/macro benchmarks written in Java and other languages targetting the JVM.

package org.openjdk.jmh.samples;

import org.openjdk.jmh.annotations.Benchmark;
import org.openjdk.jmh.runner.Runner;
import org.openjdk.jmh.runner.RunnerException;
import org.openjdk.jmh.runner.options.Options;
import org.openjdk.jmh.runner.options.OptionsBuilder;

public class JMHSample_01_HelloWorld {
  @Benchmark
  public void wellHelloThere() {
    // this method was intentionally left blank.
  }

  public static void main(String[] args) throws RunnerException {
    Options opt = new OptionsBuilder()
            .include(JMHSample_01_HelloWorld.class.getSimpleName())
            .forks(1)
            .build();
    new Runner(opt).run();
  }
}

> mvn clean install
> java -jar target/benchmarks.jar JMHSample_01_HelloWorld

@Benchmark @BenchmarkMode @CompilerControl 
@Fork @Group @GroupThreads
@Level @Measurement @Mode
@OperationsPerInvocation @OutputTimeUnit
@Param @Scope @Setup @State
@TearDown @Threads @Timeout @Warmup

• jMeter
• gatling

This is effectively the missing connector between speaking to a JVM via JMX on one end and whatever logging / monitoring / graphing package that you can dream up on the other end.

jHiccup is a non-intrusive instrumentation tool that logs and records platform "hiccups" - including the JVM stalls that often happen when Java applications are executed and/or any OS or hardware platform noise that may cause the running application to not be continuously runnable.

> java -javaagent:jHiccup.jar MyProgram

Metrics provides a powerful toolkit of ways to measure the behavior of critical components in your production environment.

• Graphite
• Graphana
• Logstash
• Kibana
• Graylog2
• Fluentd

• NewRelic
• Plumbr
• AppDynamics
• Dyntrace
• Takipi
• Hyperic

• http://spin.atomicobject.com/2014/09/03/visualizing-garbage-collection-algorithms/
• http://techblog.netflix.com/2013/05/garbage-collection-visualization.html
• http://blog.sokolenko.me/2014/11/javavm-options-production.html
• https://blog.codecentric.de/en/2013/10/useful-jvm-flags-part-7-cms-collector/

• http://blog.ragozin.info/2011/09/hotspot-jvm-garbage-collection-options.html
• http://blog.tier1app.com/2014/11/19/understand-garbage-collection-log/
• http://www.tagtraum.com/gcviewer-vmflags.html

• http://fasterj.com/tools/gcloganalysers.shtml
• https://github.com/chewiebug/GCViewer
• http://www.jclarity.com/censum/

• http://www.javacodegeeks.com/2012/03/jvm-how-to-analyze-thread-dump.html
• http://www.slideshare.net/buzdin/thread-dump-analysis
• http://docs.oracle.com/javase/7/docs/api/java/lang/Thread.State.html

• https://github.com/akullpp/awesome-java
• https://github.com/aragozin/jvm-tools
• http://openjdk.java.net/projects/code-tools/jmh/

• http://youdebug.kohsuke.org/
• https://java.net/projects/tda
• http://samuraism.jp/samurai/en/index.html

• https://github.com/jmxtrans/jmxtrans
• http://www.stagemonitor.org/
• http://jamonapi.sourceforge.net/
• https://github.com/Netflix/Hystrix

• http://www.eclipse.org/tptp/home/documents/tutorials/profilingtool/profilingexample_32.html

• 1st of December, 2015, Riga
• Software Craftsmanship Conference
• 3 tracks, 30 speakers
• http://devternity.com

• 2nd-4th of March, 2016, Riga
• Come. See. Develop.
• 5 tracks, 3 days
• http://rigadevday.lv