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Java Performance: The Definitive Guide by Scott Oaks

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Chapter 2. An Approach to Performance Testing

This chapter discusses four principles of getting the results from performance testing; these principles form the basis of the advice given in later chapters. The science of performance engineering is covered by these principles.

Most of the examples given in later chapters use a common application, which is also outlined in this chapter.

Test a real application

The first principle is that testing should occur on the actual product in the way the product will be used. There are, roughly speaking, three categories of code which can be used for performance testing, each with their own advantages and disadvantages. The category that includes the actual application will provide the best results.

Microbenchmarks

The first of these categories is the microbenchmark. A microbenchmark is a test designed to measure a very small unit of performance: the time to call a synchronized method vs. a non-synchronized method; the overhead in creating a thread vs. using a thread pool; the time to execute one arithmetic algorithm vs. an alternate implementation; and so on.

Microbenchmarks may seem like a good idea, but they are very difficult to write correctly. Consider the following code, which is an attempt to write a microbenchmark that tests the performance of different implementations of a method to compute the Nth Fibonacci number:

public void doTest() {
    // Main Loop
    double l;
    long then = System.currentTimeMillis();
    for (int i = 0; i < nLoops; i++) {
        l

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