Debug/profile heap/gc in Java

HPROF

Profiler agent.
Examples:
java -agentlib:hprof=help
java -agentlib:hprof=heap=sites
java -agentlib:hprof=heap=dump
java -agentlib:hprof=cpu=samples

" By default, heap profiling information (sites and dump) is written out to java.hprof.txt (in ASCII) in the current working directory.

The output is normally generated when the VM exits, although this can be disabled by setting the “dump on exit” option to “n” ( doe=n). In addition, a profile is generated when Ctrl-\ or Ctrl-Break (depending on platform) is pressed. On Solaris OS and Linux a profile is also generated when a QUIT signal is received ( kill -QUIT pid). If Ctrl-\ or Ctrl-Break is pressed multiple times, multiple profiles are generated to the one file.  "

jmap

The jmap command-line utility prints memory related statistics for a running VM or core file.

Commands:

jmap -histo <pid>                          #show histogram of objects
jmap -dump:format=b,file=<file>    #dump heap in HPROF format (can be processed by jhat)

jstat

"The jstat utility uses the built-in instrumentation in the HotSpot VM to provide information on performance and resource consumption of running applications. "

show garbage collection info, class loading info, compilation info, etc.

visualgc

GUI to show results of jstat.

Java VisualVM

http://download.oracle.com/javase/6/docs/technotes/guides/visualvm/index.html
command:  jvisualvm

"Java VisualVM is a tool that provides a visual interface for viewing detailed information about Java applications while they are running on a Java Virtual Machine (JVM), and for troubleshooting and profiling these applications."

JConsole

"This tool is compliant with Java Management Extensions (JMX). The tool uses the built-in JMX instrumentation in the Java Virtual Machine to provide information on the performance and resource consumption of running applications."

jhat (java heap analysis tool)

"The jhat tool provides a convenient means to browse the object topology in a heap snapshot. This tool was introduced in the Java SE 6 release to replace the Heap Analysis Tool (HAT). "

Command:

jhat <hprof_file_name>

Eclipse MAT

 

jdb

Misc.

"As of Java SE 5.0 update 7, the -XX:+HeapDumpOnOutOfMemoryError command-line option
tells the HotSpot VM to generate a heap dump when an OutOfMemoryError occurs (see
section 1.9).
As of Java SE 5.0 update 14, the -XX:+HeapDumpOnCtrlBreak command-line option tells the
HotSpot VM to generate a heap dump when a Ctrl-Break or SIGQUIT signal is received (see
section 1.10). "

Resources

http://www.oracle.com/technetwork/java/javase/index-137495.html