Performance analysis is all about visibility—knowing what is going on inside of an application, and in the application’s environment. Visibility is all about tools. And so performance tuning is all about tools.
In Chapter 2, I stressed the importance of taking a data-driven approach to performance: you must measure the application’s performance and understand what those measurements mean. Performance analysis must be similarly data-driven: you must have data about what, exactly, the program is doing in order to make it perform better. How to obtain and understand that data is the subject of this chapter.
There are hundreds of tools that provide information about what a Java application is doing, and of course it is impractical to look at all of them. Many of the most important tools come with the JDK or are developed in open source at java.net, and even though those tools have other open source and commercial competitors, this chapter focuses mostly on the JDK tools as a matter of expedience.
The starting point for program analysis is actually not Java-specific at
all: it is the basic set of monitoring tools that come with the
operating system. On Unix-based systems, these are
sar (System Accounting
Report) and its constituent tools like
and so on.
On Windows, there are graphical
resource monitors as well as command-line utilities like
Whenever performance tests are run, data ...