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As of Nov 2016 I have am no longer endorsing or providing support for 32-bit Java on 64-bit Ubuntu. Though I have not had a chance to do performance testing, with Cloud computing, lack of documention on 32-bit Java, and hopefully Oracle has continued to tune for 64-bit, it's time to move on. |
One problem with 64-bit Java is the amount of Memory it occupies:
- As explained by Oracle, "... every native pointer in the system takes up 8 bytes instead of 4".
- 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.
As of 2011 we feel that all the majority of 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.
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This has improved due to newer algorithms such as concurrency, parallelization and generational collection. However we observe there is still significant impact. |
As suchGenerally, in many cases it is also better to scale horizontally (running multiple JVMs) as opposed to using one giant JVM. This point is true for both 32-bit and 64-bit JVMs.
At least in the cloud based environments we use, where memory is a premium, 32-bit Java makes more sense.
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 and of course take full advantage of the system memory.
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We have not encountered in our own benchmarking, but here is a an example of 64-bit Java performing better than 32-bit Java on a 64-bit OS. The accepted theory here is that this is due to the emulation mode required by the 64-bit OS to run 32-bit Java. Again, we have yet to have encountered this in our usage. |
JVM | Operating System | Maximum Heap Size | Reference |
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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 |
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No, the point is to closely look at your application profile, user base and hardware and determine if you really do need to use a 32-bit or 64-bit JVM.makes sense. In some cases, 64-bit is actually faster (depending on the hardware and OS).
It has just been in our experience that often our profiles fall in,
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More details explaining the mechanics can be put here or linked in another document. |
Good review of differences and pros and cons - http://java.dzone.com/articles/should-i-use-32-or-64-bit-jvm