To see the availability of HPjmeter metrics from hprof data collection, see –Xeprof and –agentlib:hprof Profiling Options and Their Corresponding Metrics (page 65). For additional information on collecting heap dump data, see the Java™ Troubleshooting Guide for HP-UX Systems.

NOTE:

With the addition of JVMTI in JDK 5.0, the -agentlibswitch is the preferred way to activate tools such as hprof. With -agentlib, you can take advantage of improvements in JDK 5.0 and reduce the impact of data sampling on application performance. While -Xrunhprofcan still be used to specify the JVM agent with Java 5 versions, the impact on application performance is significantly greater than when using -agentlib.

You will still need to use -Xrunhprofto specify the hprof agent for earlier supported versions of Java (1.4.x).

Here are the supported -agentlib:hprofoptions that affect the collection of profile data:

Table 5-2 Supported -agentlib:hprofoptions

heap=dumpsitesall

The heap dump shows all objects remaining in memory at the time of

 

the dump. The allocation sites show where the objects were created

 

during the execution of the program. Heap analysis can be used to

 

locate memory leaks, and the allocation sites can be used to minimize

 

the memory usage.

 

To solve memory retention problems, the best practice is to use a signal

 

rather than the application shutdown to obtain the heap dump. When

 

the application shuts down, some references go out of scope and the

 

retention problem may get eliminated just before the heap is dumped.

 

Send the signal at the moment that you suspect the application is

 

holding references to no longer needed objects.

 

To keep the heap dump size down, try to send the signal just after a

 

full garbage collection (use -verbose:gcto be notified about the

 

garbage collections).

 

Remember that a heap dump contains all objects, not just live objects

 

 

cpu=samplestimes

cpu=samples uses sampling as the collecting technique, while

 

cpu=times uses tracing with reduction.

 

• Typically, the times collected by cpu=samplestimes are CPU

 

virtual times. However, HP-UX 11i versions use real CPU times

 

rather than CPU virtual times unless sampling is used.

 

• Some implementations of cpu=times report clock time. HPjmeter

 

tries to figure out what times actually have been collected, but

 

sometimes does not do it right.

 

• cpu=samples and cpu=times output exclusive times.

 

• Collecting heap data can be very intrusive, so we recommend that

 

you measure the method times and heap usage at different times.

 

However, it may make sense to specify heap=sites and

 

cpu=samplestimes for the same run when you want to locate

 

the allocation sites in the call graph.

 

 

thread=yn

Controls whether the stack traces collected during program execution

 

will be associated with an individual thread.

 

• By default, no thread identification information is stored

 

(thread=n).

 

• We suggest that you always specify thread=y.

 

• With the thread identification in the profile file, HPjmeter can

 

calculate the thread profile data for the entire application.

 

 

64 Profiling Applications