A. Sundararajan's Weblog

Observability highlights of Mustang

The following is list of observability highlights of Mustang (Java SE 6). This may not be exhaustive. I may have missed few things!

• jhat - Java Heap Analysis Tool

  This is a new command line tool [HAT +fixes+improvements + OQL (Object Query Language)]. Helps in analyzing OOM situations. More info is here:

  • Heap dumps are back with a vengeance!
  • Heap Dump Snapshots
  • What's in my Java heap?
  • Querying Java heap with OQL

• jmap -dump option

  With this option, jmap dumps snapshot of heap in binary HPROF format. The resultant dump can be analyzed with jhat

• jstack -l option

  With this new option, jstack prints java.util.concurrent locks and possible deadlocks due to those locks. More info here: jstack.

• jstack in Windows

  jstack displays Java stack traces for live processes (only).

• jmap -dump in Windows

  dumps Java heap snapshot in a file for live processes (only). Window version supports just "jmap -dump:format=b,file= <pid>" and not the other options. (jmap -histo is also being considered. So, this may change before Mustang FCS!)

• jmap -permstat prints info on intern Strings

  Internalized Strings are stored in permanent generation. Sometimes too many interned Strings may result in OutOfMemoryError. jmap -permstat option now prints total number and size of internalized String instances.

• Better OutOfMemoryError reporting

  New JVM option -XX:+HeapDumpOnOutOfMemoryError to force heap dump on OOM. More info here: OutOfMemoryError looks a bit better!

• Improved DTrace support

  There are many built-in DTrace probes in Mustang. More info is here:

  • Built-in DTrace probes in Mustang
  • Example DTrace scripts for Hotspot

• jconsole improvements

  There has been many improvements to jconsole. More info is here:

  • Getting started with jconsole just got easier!
  • Thread Dump and Concurrency Locks
  • Mustang JDK now includes attach-on-demand

• JVM Attach API

  API to load JVM agents dynamically into running applications (a.k.a "attach-on-demand"). More info is here: Using Mustang's Attach API

• Hprof includes primitive type data in heap dumps

  Apart from bugfixes, to me this is very important change: hprof now includes primitive type instance fields and primitive array content in heap dumps.

( Dec 06 2005, 12:07:24 PM IST ) Permalink Comments [2] | | | | |