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From Wade Chandler <wchand...@redesetgrow.com>
Subject Re: Max possible ram usage
Date Wed, 21 Jul 2004 13:42:58 GMT
Wade Chandler wrote:

> 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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> 
> 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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> 
> 
> 
Almost forgot...you also need to leave room for the JVM in the memory 
you allocate for the max.  Else it won't be able to peform properly it's 
own management tasks.

Wade


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