Having used JRockit for years (mostly sitting beneath WebLogic) I've been waiting for something like this book to arrive and lift the lid off the JVM to show what's inside. I'm glad to say that I am not disappointed. This book is a must-have for any serious enterprise Java developer or administrator who uses JRockit and wants to better understand how to tune, manage and monitor the JVM. The book also provides the Java developer with a clearer direction on the do's and don't's for developing a well behaving application on top of JRockit, especially in regard to memory management and thread management. Even for users of other JVMs, like Hotspot, much of the first half of the book, which concentrates on the JVM's internals, is relevant and insightful into the workings of Java virtual machines generally.
The first half of the book concentrates on providing in-depth knowledge of JRockit's internals and focusses on:
- Code Generation (Java bytecode, generation of native code, JRockit 's Just In Time compilation strategy with subsequent optimised code re-generation)
- Memory Management (heap usage, thread-local allocation, garbage collection strategies, deterministic-GC, 32-bit vs 64-bit memory management, potential pitfalls)
- Threads and Synchronisation (green vs O.S. threads, synchronisation patterns/anti-patterns, code generation strategies for locking/unlocking, thin and fat locks, lock profiling)
- Benchmarking and Tuning (throughput vs latency, tuning tips, benchmarking tips)
As I read this book, it became evident that the JRockit engineers are extremely passionate about their work and that they live and breath it. It is re-assuring to know that they are constantly striving to improve the product, based on deep scientific theory yet always with an eye on pragmatism and real-world usage. I'm sure this is why JRockit is fast and powerful whilst remaining easy to manage and run applications on. Throughout the book, the ethos of JRockit's design is very clear. It's an adaptive JVM, where the internal runtime is constantly and automatically being re-evaluated and re-tuned, according to the current nature of the hosted application's usage and load. Reading the book, I can better appreciate the argument that server-side Java is faster than an equivalent native C application. A native application only has one-shot, at compile time, to generate optimal native code. JRockit, however, takes the opportunity to revisit this at runtime, when it has a much better idea of actual usage patterns.
The second half of the book provides an introduction and detailed reference into JRockit's rich and powerful management and monitoring toolset, including:
- JRockit Mission Control (JRMC), composed of the Management Console, the Flight Recorder (plus Runtime Analyzer which it replaces) and the Memory Leak Detector
- JRockit Command line tool (JRCMD), including in-depth examples of all the important commands
- JRockit Management APIs, including the Java API for direct in-line access to the JRockit JVM from hosted Java applications plus the JMX version of the API for remote access to the JRockit JVM
Finally, at the end of the book there is an introductory chapter covering JRockit Virtual Edition (VE). JRockit VE enables the JRockit JVM, accompanied by a small JRockit kernel, to be run in a virtualised environment. This runs directly on-top of a hypervisor (eg. Oracle VM) without requiring the use of a conventional, heavy-weight, general-purpose operations system such as Linux, Solaris or Windows. Such a fully functional operating systems would otherwise burden the system with a layer of unwanted latency. This chapter in particular makes me realise that the JRockit Engineers are proverbial Rocket Scientists (or should that be Rockit Scientists? :D ). I defy anyone not to be impressed by the ambition of JRockit VE and and the high level of technical expertise that must have gone into developing it!
To summarise, I highly recommend this book. Easy to read yet very insightful. Once you've read it, it will remain as a handy reference to come back to, especially when needing to use the JRMC tools to diagnose issues and tune the JVM and hosted applications.
Song for today: Speed Trials by Elliot Smith
