Using the classes perspective

The classes perspective displays the density of class loading over time, which classes were loaded at which time, and whether a class was loaded from the class sharing cache. You can also request the collection of class histogram data to see a snapshot of the classes that are in the heap, and the amount of heap space that the class instances are occupying.

The class loading timeline

The class loading graph gives a visual indication of how much class loading occurred in your application over time. Use the graph to identify points in time at which classes were loading at a rate you did not expect.

The classes loaded table

The classes loaded table gives a more detailed view of which classes have been loaded at which times. This table also indicates whether the class was loaded from the shared classes cache.

Column heading	Description
Time loaded	The time, measured from Java™ Virtual Machine (JVM) start time, when the class was loaded.
Shared cache	Whether the class was loaded from the shared classes cache. Not all classes can be cached.
Classname	The full name of the loaded class.

You can select the time interval for displaying data, and making recommendations, by using cropping. For further information about cropping, see Cropping data.

The class histogram

The class histogram shows which classes are on the heap, the number of instances that exist for each class, and the amount of heap space that those instances are occupying. You can use this information to help diagnose memory problems.

This data comes from a snapshot of the heap; to trigger the snapshot and populate the histogram, click the Collect histogram data button in the Class histogram view. You can also trigger a snapshot from the Monitored System menu: click Monitored System > Collect histogram data.... There might be a short delay before the data is displayed.

Note: Due to a JVM limitation, class histogram data is not available if you attached the Health Center agent to a running application (see Starting the Health Center agent after starting an application (Java applications only) ). You can still attempt to trigger a snapshot, but no data is received. You might see the following message in the agent error log:

healthcenter: cannot setTags on classes: rc = 99

You can ignore this message.

Filtering the data

Use the text box before the classes loaded table, or the class histogram, to filter the output. For further information about filtering, see the filtering help topic.