The heap is the largest consumer of memory in a Java application, but the JVM will allocate and use a large amount of native memory. And while Chapter 7 discussed ways to efficiently manage the heap from a programmatic point of view, the configuration of the heap and how it interacts with the native memory of the operating system is another important factor in the overall performance of an application.
This chapter discusses these aspects of native (or operating system) memory. We start with a discussion of the entire memory use of the JVM, with a goal of understanding how to monitor that usage for performance issues. Then we’ll discuss various ways to tune the JVM and operating system for optimal memory use.
The heap (usually) accounts for the largest amount of memory used by the
JVM, but the JVM also uses memory for its internal operations.
This non-heap memory is
native memory. Native memory can also be allocated in applications
JNI calls to
and similar methods, or when using NIO). The total of native and heap
memory used by the JVM yields the total footprint of an application.
From the point of view of the operating system, this total footprint is the key to performance. If enough physical memory to contain the entire total footprint of an application is not available, performance may begin to suffer. The operative word here is “may.” There are parts of native memory that are really only used during startup (for instance, ...