•When you select a high level of detail, 1 to 20 minutes, and the heap size does not go to the local maximum before a garbage collection happens, it could indicate excessive calls to System.gc(). See Identifying Excessive Calls to System.gc() (page 41).

•When you select coarse granularity, 1 to 24 hours, you may notice the overall change of behavior in heap size and garbage collection pattern. This can help with understanding the correlation between the application load and the pressure on the heap.

If there is plenty of gray in selected areas of the display, this means that the heap was too small for the load imposed on the application at that time.

Details

You can pause and resume [p. 181] the display scrolling using the clock icon.

Related Topics

•Identifying Excessive Calls to System.gc() (page 41)

•Determining the Severity of a Memory Leak (page 43)

•Reviewing the Percentage of Time Spent in Garbage Collection (page 41)

Garbage Collections

Displays garbage collection events over the period that the application has been running and an estimated percentage of time spent in garbage collection. These events include collection from the young, old, and survivor objects in the heap. This display does not include objects in the permanent generation space. (See Basic Garbage Collection Concepts (page 87) if you are unfamiliar with these terms.) When running your application with Java 5.0.12 or later or with Java 6.0.01 or later, the visualizer can show major versus minor garbage collections.

NOTE: For detailed garbage collection information, run your application with —Xverbosegcor —Xloggcoptions and view the results in the GC viewer. See Obtaining Garbage Collection Data (page 80) and Using Specialized Garbage Collection Displays (page 157) for information on collecting and viewing garbage collection data in HPjmeter.

Figure 8-6 Monitoring Metric: Garbage Collections

Using Monitoring Displays 123