Monitor Memory and/or Heap Activity Menu

Heap Monitor

Displays free and used memory sizes in the heap and garbage collection events over time. The used heap space includes live objects and dead objects that have not yet been collected as garbage. Specifically, this visualizer shows the heap in use by objects in the eden space and in the old and survivor generations, but does not include the permanent generation. (See Basic Garbage Collection Concepts (page 87) if you are unfamiliar with these terms.)

This display indicates whether your application is doing many allocations, which typically correspond to the load level, or if your application is idle.

Figure 8-5 Monitoring Metric: Heap Monitor

Guidelines

•Look for extra-wide garbage-collection bars, which correspond to garbage collection pauses. These could cause transient service-level objective violations.

To reduce intermittent long garbage collection pauses try changing the garbage collection algorithm with a JVM option. Refer to your JVM documentation.

•If the garbage collection events still take a long time, it may indicate a paging problem where the physical memory available to the application is too small for the specified maximum size.

The remedies include:

—Decrease the maximum heap size, with a corresponding decrease in the maximum load supported by your application.

—Remove other load from the system.

—Install more physical memory.

122 Using Visualizer Functions