A. Sundararajan's Weblog

Yes, there is also fifth way :-)

In my previous post on heap histograms, I missed another way to view histogram. Thanks to Alan Bateman for pointing out the same in his comment! Here it is:

The fifth way! Use the heapViewer demo JVM TI agent shipped with JDK.

On Windows:
    java -agentpath:%JAVA_HOME%\demo\jvmti\heapViewer\lib\heapViewer.dll MainClass

On Unix:
    java -agentpath:$JAVA_HOME/demo/jvmti/heapViewer/lib/libheapViewer.so MainClass

You can look at the source code of this heapViewer agent under $JAVA_HOME/demo/jvmti/heapViewer/src directory. If you want to learn about JVM TI agents, you may want to read Kelly's blog on agents.

( Feb 17 2006, 08:24:17 PM IST ) Permalink Comments [2] | | | | |

4 ways to view Java heap histogram with Mustang

With Mustang (Java SE 6), there are atleast 4 ways to get histogram of Java heap:

1. Using jmap

   
       jmap -histo <pid-of-java-process>
   
   

2. Using -XX:+PrintClassHistogram option when starting the java application. With this option, whenever SIGQUIT signal is sent (pressing Ctrl-\ on Unix, Ctrl-Break on Windows), heap histogram is printed.
3. Using jmap tool to dump heap dump and viewing the same using jhat

   
       jmap -dump:format=b,file=heap.bin <pid-of-java-process>
       jhat heap.bin
   
   

   When jhat is started, visit the URL "http://localhost:7000/" and click on "Show heap histogram" link to view the histogram.
4. Using DTrace with Mustang. The following D-script accumulates count and total size in aggregates -- which can be printed on END probe. This script uses object-alloc probe. More details on Mustang built-in DTrace probes can be found in Keith's blog

   
       hotspot$1:::object-alloc {
           self->str_ptr = (char*) copyin(arg1, arg2+1);
           self->str_ptr[arg2] = '\0';
           self->classname = (string) self->str_ptr;
           @allocs_count[self->classname] = count();
           @allocs_size[self->classname] = sum(arg3);
       }
   

( Feb 17 2006, 03:39:07 PM IST ) Permalink Comments [1] | | | | |