One problem with 64-bit Java is the amount of Memory it occupies. As of 2011 we feel that all application profiles we have encountered do not require 64-bit Java as they often do not take advantage of using more than than 1-2GB of memory. Also, we have observed that when a Java Application has access to a large amount of memory, the application gets bogged down when garbage collection occurs.
This has improved due to newer algorithms such as concurrency, parallelization and generational collection. However we observe there is still significant impact.
As such, in many cases it is better to scale horizontally (running multiple JVMs) as opposed to using one giant JVM.
Just to be clear, you still should use a 64-bit Operating Systems. A 64-bit Operating System will allow a 32-bit JVM to come closer to the theoretical 4GB memory limit.
JVM |
Operating System |
Maximum Heap Size |
|---|---|---|
32-bit |
32-bit Windows |
1.4GB to 1.6GB |
32-bit |
32-bit Solaris |
2GB |
32-bit |
64-bit Solaris |
approaching 4GB |
32-bit |
64-bit Ubuntu |
|
* Due to various additional constraints such as available swap, kernel address space usage, memory fragmentation, and VM overhead, in practice the limits will vary.
More details explaining the mechanics can be put here or linked in another document.