HPjmeter 4.2 User's Guide

Figure 8-24 Class Types Pop-up Window

Guidelines

• Class types reside in the Permanent Generation space, which is usually more limited in size

than other areas of memory. Continuing incorporation of additional instances of a class

loader can begin to fill this area, creating an out-of-memory error in the Perm Gen region

of memory. Check the Class Loaders metric — are the number of instances of each class

loader what you expect?

• Use Mark and Find functions in the visualizers to locate references to the class loader and

its loaded classes in other related visualizers. Do you find any classes that you think should

have been garbage collected, but are not? Note how much space is held by the class loader.

Garbage collection cannot be thorough when application code has created a reference that

is keeping the class loader and its classes active beyond the time they are needed in the

program.

TIP: If you have instrumented the application with Java Management Extensions, you can also

open a monitoring session in HPjmeter and use the JMX Memory Tab (page 49) to quickly observe

a rough gauge of activity in various regions of the allocated memory, including the Perm Gen

and the Survivor space. See Using the JMX Viewer (page 47) for additional information.