DTrace is a dynamic tracing framework, initially developed by Sun for the Solaris 10 OS. Since some early beta version of the Java 1.6 JDK, the JVM (at least on Solaris) has incorporated a number of DTrace probes that allow DTrace to extract data from a program running within the JVM at runtime.

I initially used DTrace for Java to study the interaction of the OS with the JVM on the I/O front. I then understood that my scripts might be useful to a number of people doing low level performance analysis so I spent some time to make them a bit more generic and easy to use.

You can download the Java DTrace Toolkit from here

The JDT has been presented in the following short paper:

G. Gousios and D. Spinellis, “Java Performance Evaluation Using External Instrumentation,” in Proceedings of the 12th Pan-Hellenic Conference on Informatics, 2008, pp. 173–177.

The scripts

Script Function
jprofiler Reports the methods and classes that consume most execution time. Can aggregate results by package name.
jmemstats Report object allocation statistics. Can aggregate results by package name and filter results by specific package names.
jlockstat Reports methods initiating locking opera- tions in native code.
jiosnoop File management statistics: which classes cause I/O traffic?
jcallgraph Display a Java function call graph from Java to the OS kernel.
jgcsnoop Reports garbage collection statistics: frequency, duration.

Output examples

jmemstats

Java Method                            objects alloc
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
java/lang/StringCoding$StringEncoder.encode      486
java/util/HashMap.newKeyIterator                 221
org/[...]/buf/CharChunk.toStringInternal         142
java/io/UnixFileSystem.resolve                   131
java/lang/String.substring                       122
java/lang/StringCoding$StringDecoder.decode      108
java/net/Socket.getInputStream                   100
java/lang/AbstractStringBuilder.expandCapacity   99
java/lang/Object.clone                           91
java/io/UnixFileSystem.list                      74

jlockstat

Java Method                                  Native      cnt
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
java/io/UnixFileSystem.getBooleanAttributes0 malloc      367
java/io/UnixFileSystem.getBooleanAttributes0 free        363 
java/lang/ClassLoader.defineClass1 free 288 java/lang/ClassLoader.defineClass1 malloc 290 java/io/UnixFileSystem.getLastModifiedTime free 136 java/io/UnixFileSystem.getLastModifiedTime malloc 136 java/io/UnixFileSystem.list readdir64_r 134

jiosnoop

Java Method                                     syscall  cnt
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ org/apache/coyote/Response.action sosend 7 org[...]Http11Processor.action read 7 org/[...]OutputStreamOutputBuffer.doWrite sosend 2 org/[...]Http11ConnectionHandler.processConnect read 1 org[...]/mapper/Mapper.internalMapWrapper _read 1