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From Peter Stavrinides <>
Subject Re: Tomcat with 8 GB memory
Date Sun, 29 Jul 2007 12:34:36 GMT
Some of arguments presented hold some truths, but look at the bigger 
picture... the point is that 64bit is a superior architecture to 32 bit, 
but it is still maturing... the reasons for this are both hardware and 
software related... the way we write programs will have to change to 
take advantage of the new architecture, and the current generation of 
hardware will no doubt mature to realize the potential of 64bit 

32 bits processors can represent numbers up to 4,294,967,295 while a 
64-bit machine can represent numbers up to 18,446,744,073,709,551,615. 
For modern hardware to take advantage of the processing power of the 64 
bit architecture a system must have a minimum 4GB Ram, but probably 
needs significantly more and more importantly the CAPACITY to take full 
advantage of it, allocating it to running processes, with less there is 
potential for lag. 

64bit machines have been around since the 60's but only now are software 
and hardware vendors supporting it for the mainstream market. So is 
64bit better than 32bit right now? the answer is yes, a 64-bit processor 
has more technology, a better design with more transistors, thus faster 
speeds are possible. This is currently where the true benefit of 
switching to a 64-bit processor lays, it has nothing to do with the 
memory address space, which is exactly that, just space for more complex 


Alexey Solofnenko wrote:
> No, each of two 4GB processes will have only a half of the objects 
> under the same load. And I heard that GC does not scale linear with 
> heap size. And this is without multi-threading performance 
> considerations.  As usual, your mileage may vary and only tests can 
> tell for sure.
> - Alexey.
> Caldarale, Charles R wrote:
>>> From: Alexey Solofnenko [] Subject: Re: 
>>> Tomcat with 8 GB memory
>>> I was under impression that GC does not scale linearly. That means 
>>> one 8GB process will be slower than two 4GB processes.
>> Not true.  The time of a full GC using modern algorithms depends mostly
>> on the number and type of live objects, not the amount of heap space.
>> The number and type of live (reachable) objects stays relatively
>> constant for most application once the ramp-up period is over.
>> Consequently, running a single JVM with the largest heap you can fit in
>> the process space is the most efficient from a GC point of view.  (Of
>> course, there are plenty of other reasons not to put all your eggs in
>> one basket.)
>>  - Chuck
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Peter Stavrinides
Albourne Partners (Cyprus) Ltd
Tel: +357 22 750652 

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