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6.3.1 Performance

IBM’s Java implementation appears to run most code faster than the Sun im- plementation. Benchmarking something as complex as a Java Virtual Machine is well beyond our scope here (and, in fact, coming up with a benchmark that will actually predict how much faster your application will run on one environ- ment versus another is practically impossible). Nonetheless, we have seen some fairly dramatic performance improvements when running Java applications under the IBM JVM—improvements on the order of 50%–100%.

It is interesting to note that it does not matter which Java SDK produced the bytecode files. We see these improvements when the compiled classes are run, no matter which compiler (IBM’s or Sun’s) was used to produce them. This suggests that it is some combination of a faster virtual machine and/or a better Just-In-Time compiler (JIT) that gives IBM’s runtime its apparent performance advantage.

For the most part, we use the Sun development kit and runtime, simply because Sun’s is the definition of Java. But if execution speed is proving to be critical for your application, consider the IBM Java runtime. You may see some speed advantages.