Using the dump viewer

System dumps are produced in a platform-specific binary format, typically as a raw memory image of the process that was running at the time the dump was initiated. The SDK dump viewer allows you to navigate around the dump, and obtain information in a readable form, with symbolic (source code) data where possible.

You can view Java™ information (for example, threads and objects on the heap) and native information (for example, native stacks, libraries, and raw memory locations). You can run the dump viewer on one platform to work with dumps from another platform. For example, you can look at Linux® dumps on a Windows platform.

You can also explore the dump file by using Monitoring and Diagnostic Tools - Interactive Diagnostic Data Explorer. This tool is a GUI-based version of the dump viewer, which provides extra functionality such as command assistance and the ability to save the tool output.

Dump viewer: jdmpview

The dump viewer is a command-line tool that allows you to examine the contents of system dumps produced from the JVM. The dump viewer requires metadata created by the jextract utility, if the system dump was generated by a version of the J9 virtual machine before V2.6. To check the version of a JVM, use the java -version command and examine the output. The dump viewer allows you to view both Java and native information from the time the dump was produced.

jdmpview is in the directory sdk/bin.

To start jdmpview, from a shell prompt, enter:

jdmpview  -zip <zip file>

jdmpview  -core <core file> [-xml <xml file>]

The jdmpview tool accepts these parameters:

-core <core file>: Specify a dump file.
-notemp: By default, when you specify a file by using the -zip option, the contents are extracted to a temporary directory before processing. Use the -notemp option to prevent this extraction step, and run all subsequent commands in memory.
-xml <xml file>: Specify a metadata file. jdmpview guesses the name of the XML file if the -xml option is not present. This option is not required for core files generated from a J9 2.6 or later virtual machine.
-zip <zip file>: Specify a compressed file containing the core file and associated XML file (produced by jextract).

Note: The -core and -xml options can be used with the -zip option to specify the core and XML files in the compressed file. Without the -core or -xml options, jdmpview shows multiple contexts, one for each source file that it identified in the compressed file. For more information, see Support for compressed files.

After jdmpview processes the arguments with which it was started, it shows this message:

For a list of commands, type "help"; for how to use "help", type "help help"
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When you see this message, you can start using commands.

When jdmpview is used with the -zip option, temporary disk space is required to uncompress the dump files from the compressed file.

jdmpview uses the system temporary directory, /tmp.

An alternative temporary directory can be specified using the Java system property java.io.tmpdir. jdmpview shows an error message if insufficient disk space is available in the temporary directory. Use the -notemp option to prevent jdmpview from creating these temporary files. The temporary files are deleted when jdmpview exits or when you enter the close command on the command line.

You can significantly improve the performance of jdmpview against large dumps by ensuring that your system has enough memory available to avoid paging. On large dumps (that is, ones with large numbers of objects on the heap), you might have to run jdmpview using the -Xmx option to increase the maximum heap available. You might also have to increase the maximum heap size if you use the -notemp option, especially if you are analyzing a large heap, because this option specifies that all analysis is done in memory.

jdmpview  -J-Xmx<n> -zip <zip file>

To pass command-line arguments to the JVM, you must prefix them with -J.

Note:

The IBM XML implementation is deprecated in IBM® SDK, Java Technology Edition, Version 8 and will be replaced by the Oracle XML implementation in a future release. End of changes for service refresh 3