Capturing Heap Dumps

Different ways to capture a heap dump.

2 minute read

You may be aware by now, there are many different ways of getting data from the JVM. Here are just a few ways to get heap dump of the JVM.

jcmd

With jcmd, you have the ability to invoke the GC.heap_dump command. This requires that you are running as the same OS user as the target JVM process.

jcmd <PID> GC.heap_dump my_little_heap_dump.hprof

Note: If a full path is not specified, the heap_dump will be created relative to the location from where the process was started (when generated with jcmd)

jmap

A more traditional approach is using jmap and invoking the command on the target process.

jmap -dump:format=b,file=my_little_heap_dump.hprof <PID>

Core Dump

You can also use jmap to extract a heap dump from a core dump on the process:

sudo gdb --pid=<PID>
gcore /tmp/jvm.core
detach
quit
jmap -dump:format=b,file=my_little_heap_dump.hprof /usr/bin/java /tmp/jvm.core

💡 Capturing a heap dump from a core dump on Java 8, you may run into this issue: JDK-8073606.

HotSpot Diagnostic MBean

You can capture a heap dump by invoking a diagnostic MBean which is included in the Oracle JDK. You can do so by opening your favorite MBean browser (ex. jconsole, jmc) and invoke the com.sun.management.HotSpotDiagnostic. The arguments are:

  • Filename of the heap dump that will be created. 💡 Note, it will be created with file ownership of the hosting JVM process.
  • Indicator to dump all live object (true will dump only live objects)

hotspot_diag

 


  Up Next

In the next section, we'll start analyzing our heap dump with JOverflow.

JOverflow