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Java performace issue in 32 bit Red Hat

Ankit Thakkar
Ranch Hand

Joined: Apr 29, 2005
Posts: 33

Dear All,

We are using 32 bit Red Hat Linux with 10 GB Physical Memory. JVM allows us to allocate max heap size as 2GB. But we have requirement to allocated more than 2GB. Is there any way I can allocate more heap size then 2GB.

Please help us as we are struggling with Performance issue in production

Peter Johnson

Joined: May 14, 2008
Posts: 5852

32-bit applications are limited to 4GB of memory. Some of that space (usually around 1GB on Linux and 2GB on Windows) is reserved for the operating system's use (for things such as file handles). The rest of the space is used by the code (the app itself and its shared libraries or DLLs) and the app's data. The heap is only one of the many data areas used by the JVM (others include the thread stacks, perm gen and C/C++ data structures used by the JVM).

The JVM heap size is limited to the largest contiguous memory block that can be allocated. On most 32-bit Linux systems this turns out to be around 2GB. On Windows it is around 1.4GB.

If you need a larger heap, you will have to move to a 64-bit operating system and run a 64-bit JVM.

JBoss In Action
Prashant R Kataria

Joined: Jul 23, 2007
Posts: 20
Yes what peter said is correct, you will not get more than 2GB of space in 32bit unix or windows system. However, on 32bit solaris machine you will get 3GB of memory.

But I would advise that you make sure that you really need memory more than 2GB. If you really do then you should go for 64bit environment.

Prashant Kataria
SCJP 5.0

"If you are going through hell, keep going!!!"
Kees Jan Koster
JavaMonitor Support

Joined: Mar 31, 2009
Posts: 251
Here's some more background, and some links to additional reading

Java-monitor, JVM monitoring made easy <- right here on Java Ranch
I agree. Here's the link:
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