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From "Caldarale, Charles R" <>
Subject RE: [OT] Question on JVM maximum heap size parameter in tomcat
Date Thu, 02 Aug 2007 18:01:40 GMT
> From: Monimoy Deb [] 
> Subject: Question on JVM maximum heap size parameter in tomcat
> So, I am looking for the logic for specifying optimum
> value for Xmx parameter which I can specify without
> any manual intervention.

This has nothing to do with Tomcat per se, but rather with JVM

Maximum heap size also has nothing to do with the amount of RAM on your
system.  Instead, it is limited by the largest contiguous are available
within the process virtual space.  On most 32-bit systems, the process
virtual space is limited to 2 GB, but some of this must be allocated to
code and data structures necessary for operation of the process.
Fragmentation may also occur within the process virtual space, further
limiting the maximum heap size.

The amount of RAM does come into play when taking performance into
account, of course, since a heap that exceeds the available RAM is
likely to suffer from significant paging activity.

The net result is that there is no guaranteed or automatically
calculable maximum heap setting - you have to experiment for the
platform you're running on.

 - Chuck

P.S. Things work better when -Xms = -Xmx.

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