Java Performance Tuning

System Limitations and What to Tune

Three resource s limit all applications:

• CPU speed and availability

• System memory

• Disk (and network) input/output (I/O)

When tuning an application, the first step is to determine which of these is causing your application to run too slowly.

If your application is CPU-bound, you need to concentrate your efforts on the code, looking for bottlenecks, inefficient algorithms, too many short-lived objects (object creation and garbage collection are CPU-intensive operations), and other problems, which I will cover in this book.

If your application is hitting system-memory limits, it may be paging sections in and out of main memory. In this case, the problem may be caused by too many objects, or even just a few large objects, being erroneously held in memory; by too many large arrays being allocated (frequently used in buffered applications); or by the design of the application, which may need to be reexamined to reduce its running memory footprint.

On the other hand, external data access or writing to the disk can be slowing your application. In this case, you need to look at exactly what you are doing to the disks that is slowing the application: first identify the operations, then determine the problems, and finally eliminate or change these to improve the situation.

For example, one program I know of went through web server logs and did reverse lookups on the IP addresses. The first version of this program was very slow. A simple analysis of the activity ...