IBM User Guide for Java V7 on Windows > Troubleshooting and support > Using diagnostic tools > Overview of the available diagnostic tools
Summary of diagnostic information
In general, the production of this diagnostic data happens under default conditions, but can be controlled by starting the JVM with specific options (such as -Xdump; see Using dump agents). Older versions of the IBM JVM controlled the production of diagnostic information through the use of environment variables. You can still use these environment variables, but they are not the preferred mechanism and are not discussed in detail here. Environment variables lists the supported environment variables).
The format of the various types of diagnostic information produced is specific to the IBM JVM and might change between releases of the JVM.
The types of diagnostic information that can be produced are:
- Javadump
- Human-readable format produced by default when the JVM terminates unexpectedly because of...
- An operating system signal
- An OutOfMemoryError exception
- When the user enters a reserved key combination (for example, Ctrl-Break on Windows)
- Calling com.ibm.jvm.Dump.JavaDump() from inside the application
A Javadump summarizes the state of the JVM at the instant the signal occurred. Much of the content of the Javadump is specific to the IBM JVM.
Sometimes referred to as a Javacore or thread dump.
- Heapdump
- Generated...
- At the request of the user (for example by calling com.ibm.jvm.Dump.HeapDump() from inside the application)
- When the JVM terminates because of an OutOfMemoryError exception
You can specify finer control of the timing of a Heapdump using...
-Xdump:heap
For example, you could request a Heapdump after a certain number of full garbage collections have occurred. The default Heapdump format (phd files) is not human-readable and you process it using available tools such as Heaproots.
- System dumps
- Platform-specific files that contain information about the active processes, threads, and system memory. System dumps are usually large. By default, system dumps are produced by the JVM only when the JVM fails unexpectedly because of a GPF (general protection fault) or a major JVM or system error. You can also request a system dump by calling...
com.ibm.jvm.Dump.SystemDump()
To produce system dumps when other events occur, you can use...
-Xdump:system
Known as core dumps on Linux platforms.
- Garbage collection data
- A JVM started with the -verbose:gc option produces output in XML format that can be used to analyze problems in the Garbage Collector itself or problems in the design of user applications. Numerous other options affect the nature and amount of Garbage Collector diagnostic information produced.
- Trace data
- The IBM JVM tracing allows execution points in the Java code and the internal JVM code to be logged. The -Xtrace option allows the number and areas of trace points to be controlled, as well as the size and nature of the trace buffers maintained. The internal trace buffers at a time of failure are also available in a system dump and tools are available to extract them from a system dump. Generally, trace data is written to a file in an encoded format and then a trace formatter converts the data into a readable format. However, if small amounts of trace are to be produced and performance is not an issue, trace can be routed to STDERR and will be pre-formatted.
- Other data
- Special options are available for producing diagnostic information relating to
The SDK includes a JVMTI based profiling tool called HPROF, which produces information that can help you to determine the parts of an application that might be using system resources; see Using the HPROF Profiler for more details.
The SDK also includes an unsupported, experimental tool called JConsole. This graphical monitoring tool is based on the java.lang.management API, which you can use to observe and, for some properties, control various aspects of the JVM's behavior.
Parent: Overview of the available diagnostic tools
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