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I want to chose a value for maximum JVM heap size. I have some questions about it.

1) Is it usually related with the available physical memory size on the system? If so, is there any formula about this?

2) For the 32-bit JVM, can I set a value larger than 4GB even if the physical memory is very large?

3) Do I need to consider some impact of OS (e.g. Windows, Linux)?

Thanks

steve lin
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1 Answers1

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1.) Yes amount of memory you can allocate to JVM is related to physical memory available on your system. There is no fixed formula, however there is a rule of thumb that you can use to decide the memory allocation size for your process. There is memory recommendation for different Operating Systems. So (PhysicalMemory - Recommended OS memory) can be allocated to the java process. It varies for 32-bit vs 64-bit OS. If you don't have any other process then this formula will work fine. However if you have other memory consuming processes then you need to take into account memory allocation of those processes as well.

e.g. Windows 7 has following recommended requirement 1 gigabyte (GB) RAM (32-bit) or 2 GB RAM (64-bit). So, if you have 4GB physical memory then you can allocate 2GB to your process assuming 2 GB is used by OS.

2.) For 32-bit JVM you can not set the value larger than 4GB. In fact if your total physical memory is 4GB. You cannot allocate more than 2GB to your Java process. Checkout this answer for more detailed explanation

3.) Yes you should consider OS impact. Check the recommended memory configuration for different Operations Systems and decide memory for your Java process.

Hope this helps.

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Nitin Arora
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