Saturday, August 28, 2010

A simplified view of WLDF

The WebLogic Diagnostic Framework (WLDF) is a very powerful capability that has been in the product since WebLogic 9.0. WebLogic's product documentation does a good job of describing the fine detail of WLDF, but I believe that the high level overview it provides is too verbose and makes WLDF seem more complicated than it is. This is probably one reason why I don't see WLDF used quite as often as it should be, in place of custom coded monitoring solutions.

A couple of years ago I created my own diagram showing WLDF's composition, in an attempt to demonstrate that it's actually a fairly simple concept. However, I never got around to publishing it. Prompted by a recent request, I thought I'd address this ommision now, so here is that diagram...

(click image for larger view)

Hopefully this helps to better show the power of WLDF and that it's not as complex as one might think.

Song for today: Maps by Yeah Yeah Yeahs

Wednesday, August 11, 2010

Review of the new JRockit book

As promised, here's my review of the new JRockit book...

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)
Don't be put off by the early exposure to Java bytecode samples in the book. The bytecode examples are only used liberally and only in a couple of early chapters. It's worth reading these bytecode samples carefully because the points these chapters make will resonate more strongly if you do.

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
These chapters provide an easy to read introduction to the key features of JRockit's rich tools, lowering the barrier to use for newbies. Also, many of the illustrated examples are use-case driven, acting as a handy reference guide to come back to at a later date. For example, if you suspect that you have a memory leak in your application and want to work out how best to locate the root of the leak, using the tools, the Leak Detector chapter will take you by the hand through this process.

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

Wednesday, August 4, 2010

New release of DomainHealth WebLogic monitoring tool

I've just released the latest version of DomainHealth - version 0.9.

DomainHealth is an open source "zero-config" monitoring tool for WebLogic. It collects important server metrics over time, archives these into CSV files and provides a simple web interface for viewing graphs of current and historical statistics.

(click image for larger view)
This release includes a new look and feel and a new page navigation mechanism (based on some contributions from Alain Gregoire). Other new features included are Web-App monitoring, EJB monitoring and various minor improvements and tweaks. For a full list of changes see the Release Notes document listed alongside the DomainHealth download files.

You can download DH from the project home page at

The help docs for DH are at

I'd like to say a big thank you to Alain Gregoire for his valuable design and code contributions to this version of DomainHealth.

Song for today: Lets Go For A Ride by Cracker