IBM on troubleshooting Java applications

with Tags: monitoring

Monitoring and Diagnostic Tools for Java - Health Center v1.2 Released

ChrisBailey Tags: health performance java center monitoring 2,634 Visits

Health Center v1.2 has just been released with a number of new features added. The most notable of which are:

Monitoring of "native" (process address space) memory usage
Information on File I/O showing when files are opened/closed and what files are currently open
Object allocation profiling

You can find more information on the Health Center homepage, and obtain the new version of Health Center as an add-on to the IBM Support Assistant (ISA) Workbench.

Over the next few entries I'll try to cover some of the problems that can diagnosed and solved using the new features.

Monitoring an application for "native" (non-Java heap) leaks

ChrisBailey Tags: monitoring memory gcmv native java 6,225 Visits

IBM Monitoring and Diagnostic Tools for Java - Garbage Collection and Memory Visualizer (GCMV) has been able to load, graph, and carry out leak detection for "native" memory on AIX and Linux for some time. With the newly released version 2.3, it will now also do so for Windows as well!

What is "native" memory and why monitor it?

Java applications run in a virtualized Java Runtime Environment (JRE), which provides the Java heap that is commonly associated with Java memory usage as it is where Java objects are created and managed for the application.
The JRE process itself is a native process running on the Operating System (OS), in the same way as any other native process would. As such it consumes native resources, including memory. This "native" memory consumed by the JRE process includes all of its allocations, for example: the Java Virtual Machine (JVM), Just In Time (JIT) compiled code, Java Native Interface (JNI) allocations used to back Java objects, as well as the Java heap itself.

The main reason for monitoring "native" memory usage is the same as for Java heap memory: should the available memory become exhausted, an OutOfMemoryError will be generated. In addition, it's useful for understanding whether of not it's possible to increase the Java heap size should you want to. As the Java heap is one of the constituent parts of the native memory usage, increasing the Java heap size will increase the native heap usage and will lead to an OutOfMemoryError due to native heap exhaustion if it is increased to the point that the native memory usage exceeds the limit of what is available.

An excellent discussion on this topic, which includes what the OS memory limits are, is available from Andrew Hall's article "Thanks for the memory"on developerWorks.

Monitoring native memory usage in GCMV

GCMV can load and parse native memory usage data generated using svmon on AIX, ps on Linux and perfmon on Windows. Full instructions on how to generate the data are provided in the "Help" information provided by GCMV in ISA in the following section:
Tool: IBM Monitoring and Diagnostic Tools for Java - Garbage Collection and Memory Visualizer > Using Garbage Collection and Memory Visualizer > Supported data types > Native memory

Once loaded in to GCMV, the memory usage data is available as raw, structured and tabbed data, graphed to produce a line plot, and a report provided that does statistical analysis and looks for potential memory leaks.

You may have realised that, as GCMV is graphing native memory, it's not specific to Java applications so can be used for any process. In fact, the output above is from the web browser running on my desktop.

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