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From Mark Thomas <ma...@apache.org>
Subject Re: tomcat memory allocation
Date Thu, 06 Jul 2006 01:24:30 GMT
Speulman, Elly wrote:
> Hi,
> 
> Is there anyone out there who has been able to configure more than 1550M for
> Tomcat 5.0 on a Windows advanced server installation. The server has a total
> of 4Gb of memory. We are just not able to cross a border.
> Config of Tomcat memory takes place via the Tomcat configuration buttons.
> Perhaps someone even has a solution?

This is a windows limitation. Do a Google for /3GB and /PAE boot.ini
switches. The maximum memory varies by version (2003 is 32GB, 2003 SP1
is 64GB) and I can't remember them all but the short (actually quite
long) answer is:

The default windows installation has a maximum of 4GB RAM. Of this,
the kernel is allocated 2GB and user processes the rest with a maximum
per process of 2GB (although in practice is is usually around 1.6GB).

The /PAE switch should make all the physical memory in your machine
visible to windows up to the maximum supported by your OS and SP
versions. However, 2GB is still allocated to the kernel and user
process are still limited to 2GB (really 1.6GB) each.

The /3GB switch reduces the kernel allocation to 1GB and makes 3GB
(really about 2.6GB) available per user process but total memory is
still limited to 4GB.

Using both /PAE and /3GB together gets 'interesting'. kernel memory is
reduced to 1GB, user processes limited to 3GB per process and total
memory is the smallest of physical memory, OS/SP maximum and 16GB.
Note the 16GB upper limit. This caught me out recently on a 48GB
windows box.

On your box, I would use the /3GB switch but be aware of the 16GB
upper limit for total system memory in this case.

HTH,

Mark

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