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JVM performance optimization, Part 1: A JVM technology primer

Java performance for absolute beginners

By Eva Andreasson, JavaWorld.com, 08/21/12

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Page 7 of 7

A final algorithm improvement worth mentioning is compaction, which is a way to manage heap fragmentation. Compaction basically means moving objects together to free up larger consecutive chunks of memory. If you are familiar with disk fragmentation and the tools for handling it then you will find that compaction is similar, but works on Java heap memory. I'll discuss compaction in more detail later in this series.

In conclusion: Reflection points and highlights

A JVM enables portability ("write once, run anywhere") and dynamic memory management, both key features of the Java platform and reasons for its popularity and productivity.

In this first article in the JVM performance optimization series I've explained how a compiler translates bytecode to target-platform instruction languages and helps optimize the execution of your Java program dynamically. There are different compilers for different application needs.

I've also briefly discussed memory allocation and garbage collection, and how both relate to Java application performance. Basically, the higher the allocation rate of a Java application, the faster your heap fills up and the more frequently garbage collection is triggered. The challenge of garbage collection is to reclaim enough memory for your application needs without impacting running applications more than necessary, but to do so before the application runs out of memory. In future articles we'll explore the details of both traditional and more novel approaches to garbage collection for JVM performance optimization.

About the author

Eva Andreasson has been involved with Java virtual machine technologies, SOA, cloud computing, and other enterprise middleware solutions for 10 years. She joined the startup Appeal Virtual Solutions (later acquired by BEA Systems) in 2001 as a developer of the JRockit JVM. Eva has been awarded two patents for garbage collection heuristics and algorithms. She also pioneered Deterministic Garbage Collection which later became productized through JRockit Real Time. Eva has worked closely with Sun and Intel on technical partnerships, as well as various integration projects of JRockit Product Group, WebLogic, and Coherence (post Oracle acquisition in 2008). In 2009 Eva joined Azul Systems as product manager for the new Zing Java Platform. Recently she switched gears and joined the team at Cloudera as senior product manager for Cloudera's Hadoop distribution, where she is engaged in the exciting future and innovation path of highly scalable, distributed data processing frameworks.

Read more about Core Java in JavaWorld's Core Java section.

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Resources
  • "To Collect or Not To Collect." (Eva Andreasson, Frank Hoffmann, Olof Lindholm; JVM-02: Proceedings of the Java Virtual Machine Research and Technology Symposium, 2002): Presents the authors' research into an adaptive decision process that determines which garbage collector technique should be invoked and how it should be applied.
  • "Reinforcement Learning for a dynamic JVM" (Eva Andreasson, KTH Royal Institute of Technology, 2002): Master thesis report on how to use reinforcement learning to better optimize the decision of when to start concurrent garbage collection for a dynamic workload.
  • "Deterministic Garbage Collection: Unleash the Power of Java with Oracle JRockit Real Time" (An Oracle White Paper, August 2008): Learn more about the Deterministic Garbage Collection algorithm in JRockit Real Time.
  • Why is Java faster when using a JIT vs. compiling to machine code? (Stackoverflow, December 2009): A thread discussion for learning more about Just-in-Time compiler technology.
  • Zing: A fully Java compliant highly scalable software platform that includes an application-aware resource controller and zero overhead, always-on production visibility and diagnostic tools. Zing incorporates industry-leading, proven technology to allow TBs memory heap sizes per instance with sustained throughput under dynamic load and extreme memory allocation rates common for Java applications.
  • "G1: Java's Garbage First Garbage Collector" (Eric Bruno, Dr. Dobb's, August 2009): A good overview of GC and introduction to the G1 garbage collector.
  • Oracle JRockit: The Definitive Guide (Marcus Hirt, Marcus Lagergren; Packt Publishing, 2010): A complete guide to the JRockit JVM.