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WEBSPHERE PORTAL V6.1 TUNING GUIDE
Environment Considerations
Before beginning your install of WebSphere Portal you should consider how to use the
environment in order to achieve ideal performance. Topics to consider include:
• Choosing between 32-bit and 64-bit JVMs
• Use of hardware multithreading, also known as Simultaneous Multithreading or
Hyper-Threading.
3 2 - B I T A N D 6 4 - B I T C O N S I D E R A T I O N S
The choice of a 32-bit or 64-bit JVM involves some trade-offs. The key advantage of a 64-bit
JVM is its vastly larger address space. Heap sizes of 2.5GB or larger can be practical on
modern server systems. This can be a significant benefit for applications with high memory
demands.
A 64-bit JVM does have disadvantages as well. Machine instructions and memory
references in a 64-bit JVM are larger than in a 32-bit JVM. This means that Java objects,
which typically contain multiple memory references, are larger in a 64-bit JVM than
compared to a 32-bit JVM. Therefore a 64-bit JVM will need a larger heap than a 32-bit JVM
for the same population of objects.
The increased size of instructions and memory references imposes a second performance
penalty. They increase the demand on the memory subsystem of the system, causing more
cache misses and a higher demand for memory bandwidth. As a result, executing a set of
operations in a 64-bit JVM can be slower than executing the same operations in a 32-bit
JVM.
When considering a deployment of WebSphere Portal 6.1, consider the memory demands
your applications will have. If you expect a high demand for memory, the best performance
will probably come from a 64-bit JVM. On the other hand, if the memory demand is lower, a
32-bit JVM is likely to give superior performance.
H A R D W A R E M U L T I T H R E A D I N G ( H Y P E R - T H R E A D I N G )
Many modern processor architectures support hardware multithreading. For example, this is
known as Hyper-Threading (HT) on Intel processors and Simultaneous Multithreading
(SMT) on Power-series processors. Our experience is that using hardware multithreading
provides an improvement in capacity in all of the scenarios and platforms reported in this
report, so we would recommend its use on platforms where this is an option.