HPjmeter 4.2 User's Guide

• Array Leak Locations Alert (page 112)

• Class Loaders (page 150)

Checking for Proper Heap Sizing

Efficiencies in program performance can be obtained by allocating the optimal amount of memory

for the heap according to the needs of the program and the operation of the JVM garbage collection

routine. Checking activity in the heap and comparing to garbage collection frequency and duration

can help you determine optimal heap size needed for best performance from your application.

See the following sections for metrics that give insight into these aspects of the system:

• Current Live Heap Objects (page 129)

• Heap Monitor (page 122)

• Garbage Collections (page 123)

• Heap Usage Notification (page 111)

For detailed GC analysis, run your application with -Xverbosegc and use the HPjmeter GC

viewer to analyze GC activity in the heap. For additional details on memory usage, run your

application with -agentlib:hprof.

Confirming Java Memory Leaks

HPjmeter can automatically detect Java memory leaks, alerting you about the issue before the

application crashes.

After running for some time, Java applications can terminate with an out-of-memory error, even

if they initially had an adequate amount of heap space. The direct cause of this error is the inability

of the garbage collector to reclaim enough heap memory to continue.

The root cause of this problem is that some objects, due to the design or to coding errors, remain

live. Such objects, called lingering objects, tend to accumulate over time, clogging the heap and

causing multiple performance problems, and eventually leading to the application crash. Although

the nature of this phenomenon is different than memory leaks in C/C++, Java lingering objects

are also commonly called memory leaks.

A more subtle problem that can cause an out-of-memory error occurs when the Permanent

Generation area of memory becomes full of loaded classes. Running -agentlib:hprof can

provide class loading data that can help to reveal whether this problem is occurring.