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IBM Technology for Java on V6R1

One notable feature of IBM* i5/OS* V6R1 is the significant performance benefits seen in running IBM Technology for Java* on V6R1. In addition to the incremental improvements seen with every release, V6R1 introduces a 64-bit JVM* and supports 64K large pages. The addition of a 64-bit implementation of IBM Technology for Java alongside the 32-bit implementation introduced in V5R4 provides a complete solution for running Java applications on i5/OS, letting customers migrate away from the Classic JVM and choose the right IBM Technology for Java VM based on their application requirements and system resources. See Table 1 for a list of all JVMs available in V6R1.

IBM has made significant performance improvements for IBM Technology for Java in V6R1. Many applications running with IBM Technology for Java 32-bit will have performance gains of 10 percent to 15 percent in V6R1 compared with V5R4. These improvements are on top of the excellent performance delivered with the 32-bit JVM in V5R4 and the additional gains provided through Java Group PTFs. Enabling 64K page support on the 32-bit JVM can improve performance by an additional 10 percent or more compared with the default 4K page size. Most Java applications will run at least 30-percent faster in IBM Technology for Java (32-bit) than in the Classic JVM.

Another important consideration for Java applications is memory footprint. The 32-bit implementation of IBM Technology for Java reduces the memory footprint of most Java applications by 40 percent or more compared with the Classic JVM, due to improvements in garbage-collection technology and the fact that object references require less memory in a 32-bit JVM. However, the 32-bit JVM also has a limited 4 GB address space to work with, resulting in a maximum heap size of around 2.5 to 3.0 GB for most applications. The introduction of the 64-bit implementation of IBM Technology for Java in V6R1 offers a solution to this limitation. The 64-bit JVM allows for a virtually unlimited heap size while providing most of the performance benefits of the 32-bit implementation.

Because IBM Technology for Java (64-bit) requires more memory for object references than the 32-bit JVM, Java applications will generally require larger heap sizes and a greater memory footprint when running in the 64-bit JVM than when using the 32-bit JVM. However, the advanced garbage-collection algorithms in IBM Technology for Java still let most applications use smaller heaps than they require in the Classic JVM; a 10-percent or more reduction in memory footprint is typical. The 64-bit IBM Technology for Java implementation generally offers a 20-percent or more performance improvement over the Classic JVM.

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