Java Performance, 2nd Edition

Chapter 7. Heap Memory Best Practices

Chapters 5 and 6 discussed the details of how to tune the garbage collector so that it has as little effect on a program as possible. Tuning the garbage collector is important, but often better performance gains can be made by utilizing better programming practices. This chapter discusses some of the best-practice approaches to using heap memory in Java.

We have two conflicting goals here. The first general rule is to create objects sparingly and to discard them as quickly as possible. Using less memory is the best way to improve the efficiency of the garbage collector. On the other hand, frequently re-creating some kinds of objects can lead to worse overall performance (even if GC performance improves). If those objects are instead reused, programs can see substantial performance gains. Objects can be reused in a variety of ways, including thread-local variables, special object references, and object pools. Reusing objects means they will be long-lived and impact the garbage collector, but when they are reused judiciously, overall performance will improve.

This chapter discusses both approaches and the trade-offs between them. First, though, we’ll look into tools for understanding what is happening inside the heap.

Heap Analysis

GC logs and the tools discussed in Chapter 5 are great at understanding the impact GC has on an application, but for additional visibility, we must look into the heap itself. The tools discussed in this section provide ...