A. Sundararajan's Weblog

Observability Top 10 in Mustang

You may have read Top 10 Things You Need to Know about Mustang (Java SE 6) beta-2. That top 10 covers the entire JDK. This is a Java Observability top 10:

1. attach-on-demand API

   java.lang.instrument and JVM TI agents need not be loaded at the application start-up. Agents may be loaded "on demand".

   • Using JVM agents - Kelly O'Hair.
   • Late bindings agents - Alan Bateman

2. jconsole improvements
   • For local monitoring -Dcom.sun.management.jmxremote need not be used with the commandline (of the monitored application).
   • jconsole is a supported tool! - Mandy Chung
   • jconsole plugins - sample plugins (jtop, script shell)
   • UI improvements and so on.
   More details: Mustang's jconsole - Mandy Chung

3. java.util.concurrent lock information in stack traces
   • New -l option in jstack to dump java.util.concurrent locks and deadlocks due to those
   • Ctrl-Break (or Ctrl-\) handler prints util.concurrent locks if -XX:+PrintConcurrentLocks is specified in the command line

4. Java heap dumps

   Java heap snapshot can be dumped into a binary format file (a.k.a hprof binary format). The format is specified http://heap-snapshot.dev.java.net There are many ways to dump the heap

   • Using -dump option with jmap against a live process
   • Running jmap against a core dump (on Solaris and Linux)
   • Running hprof profiler with -Xrunhprof:format=b option
   • Starting the JVM with -XX:+HeapDumpOnOutOfMemoryError option - with this option JVM dumps heap when OutOfMemoryError is thrown.
   • Programatically using HotSpotDiagnosticMXBean
   More Info:
   • HeapDumpOnOutOfMemoryError - Alan Bateman
   • Heap Dump Snapshots - Kelly O'Hair
   • Heap dumps are back with a vengeance! - Alan Bateman

5. Heap dump analysis using jhat

   jhat - Java Heap Analysis Tool can be used to analyze the heapdumps produced by above means.

   • Querying Java heap with OQL
   • Using Mustang's jmap/jhat to profile GlassFish - Jean-Francois Arcand

6. DTrace Java support
   • New DTrace probes for hotspot JVM
   • Few Java level probes (such as method-entry) require you to start the JVM with -XX:+ExtendedDTraceProbes flag - this can be avoided using jinfo tool. jinfo can be used to turn on/off the flag dynamically. see below...
   • In Tiger (Java 5.0), a new DTrace built-in function named jstack() was added to print Java frames in stack traces. In Mustang, Java method signatures are shown in jstack() output

7. Turing on JVM flags dynamically

   Few JVM command line options can be turned on/off dynamically (from outside the process). Only a subset of flags - called manageable flags - can be turned on/off (or set) dynamically. Two ways:

   • Using HotSpotDiagnosticMXBean programatically or through jconsole
   • Using jinfo with -flag +/- <flag-name> option
   In addition, DTrace probes flag - ExtendedDTraceProbes flag - can also be turned on/off by jinfo

8. New tools (with subset of options) on Windows
   • jstack (-l option and no options only, for live processes only). No mixed mode stack trace support.
   • jmap (-dump and -histo options only). i.e., heap dump and heap histogram options only.
   • jinfo (-flag and -flag +/- <flag-name> options only). i.e., only printing a JVM -XX flag value or turning on/off a JVM flag dynamically (of a live process).

9. Better OutOfMemoryError!

   OutOfMemoryError looks a bit better! - better detail message and stack trace with OOM exception!

10. Misc. command line tools improvements
    • jmap prints information on internalized Strings (count and total byte size) of internalized strings is printed with -permstat option
    • New -finalizerinfo option with jmap - prints summary information on objects waiting to be finalized.

( Jun 19 2006, 09:22:12 PM IST ) Permalink Comments [1] | | | | |