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From Wade Chandler <wchand...@redesetgrow.com>
Subject Re: Max possible ram usage
Date Wed, 21 Jul 2004 13:38:26 GMT
Albrecht Marcus wrote:

> Hi everyone,
>  
> i want to run tomcat (version 5.0.25 and java j2sdk1.4.2_04) on my server with 5 GB RAM.
> The server is a hp proliant with 2x3.06 Intel Xeon.
> As i have enough ram i would allow him to use 3 GB at the max.
>  
> My java options are
> JAVA_OPTS="-Xms512m -Xmx3072m"
>  
> The tomcat won't start with this options.
>  
> This is the output of my catalina.out logfile:
> "Jul 21, 2004 2:28:12 PM org.apache.coyote.http11.Http11Protocol destroy
> INFO: Stopping Coyote HTTP/1.1 on http-8080
> Error occurred during initialization of VM
> Could not reserve enough space for object heap"
>  
> If i lower the max value i get it running with a max of 1792 MB setting (JAVA_OPTS="-Xms512m
-Xmx1792m").
>  
> Can anyone tell me the max ram size that tomcat/java can use?
> I have't found that information anywhere on the net or mailing lists.
>  
> Thank's in advance ...
>  
>  
> Marcus
> 
> _____________________________
> 
>  
> 
> Marcus Albrecht
> 
> OC-SYS / Systemadministration
> 
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> SYCOR GmbH
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>  
> 
> mailto:marcus.albrecht@sycor.de <mailto:marcus.albrecht@sycor.de> 
> 
> www.sycor.de <http://www.sycor.de/> 
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> 

Well, the real issue is with IA32.  IA32 systems currently only support 
up to 4GB of RAM per process (there are some software patches that trick 
this, but I don't know if there are any for windows or not..there are 
some for linux, but I've only read about them).  The OS kernel will use 
up the other 2GB and leaves you with 2GB (kernel has to be able to 
manage the memory...page and swap).  So unless you get an AMD32/64 or an 
Intel Itanium this is the limit you will face with the system you have 
for all processes (on 32/64 you'll need a 64-bit JVM...I think Sun makes 
one).  Of course a PowerPC64 or a Sparc64 would be able to do the same.

You could use the nio package in your application if you need to and 
create yourself some shared memory buffers and under neith this use some 
special file maps or shared memory to get around the memory issues, but 
more than likely you'll never really need that much memory.  If you 
really do then what you really need to do is to create some special 
memory class that will use a special shared memory resource for the 
operations that require huge amounts of memory and you will have to 
manage multiple chunks for shared memory pretty much.  This will also 
require you to write some native code.  basically you would make an 
implementation of java.nio.channels.FileChannel.

Linux* The large memory kernel patch may or may not help you...depends 
on the 32-bit JVM and how it is written.  I doubt it would address more 
space with a patch, though I would say that sooner or later there will 
be one that will when large memory addressing processes become more popular.

Wade


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