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From "Caldarale, Charles R" <Chuck.Caldar...@unisys.com>
Subject RE: Max heap size
Date Fri, 08 Jan 2010 14:37:43 GMT
> From: V Jayakumar [mailto:vjk@hotmail.com]
> Subject: Max heap size
> 
> OS : 32 Bit Redt Hat Enterprise Linux
> $ java -version
> java version "1.6.0_14"
> Java(TM) SE Runtime Environment (build 1.6.0_14-b08)
> Java HotSpot(TM) Client VM (build 14.0-b16, mixed mode, sharing)
> apache-tomcat-5.5.20

Useful information.

> Server has 4 GB of RAM.

Not relevant for -Xmx, but is relevant for system performance.

> What is the maximum value that can be passed to  -Xmx ?

You will need to experiment to determine the exact value, and that may change with JVM updates,
Linux patches, file usage, etc.  On a 32-bit OS, virtual process space is either 2 or 3 GB,
and the Java heap as well as numerous other memory consumers must fit inside that space. 
The RAM size has nothing to do with the heap size, but you should insure that the sum of *all*
real process spaces that are active does not exceed the available RAM, or you may start to
incur page thrashing.

Experimenting to find the largest -Xmx value for your environment should only take a few minutes.

 - Chuck


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