I was under impression that GC does not scale linearly. That means one
8GB process will be slower than two 4GB processes. There are other
considerations too: multi-threading - global locks will lock less
threads (maybe in GC, heap, application logic, ...), but cluster
overhead may be noticeable too.

- Alexey.

Christopher Schultz wrote:
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> Lightbulb,
>
> lightbulb432 wrote:
>  
>> If you have a gigantic server with something like 8 GB of memory, what would
>> be the best way to run Tomcat 6 on it? One instance, multiple instances, or
>> divide it up into two or more virtualized servers each with one instance?
>>  
>
> Unless you have concerns about stability of TC6 or your own application,
> one big JVM with a ton of threads would be my recommendation.
> Virtualization or multiple TC instances only adds overhead with no other
> real benefit. (If you run multiple applications, multiple TC instances
> might make sense).
>
>  
>> Is Tomcat meant to run as one instance with that much memory, or is it
>> optimized for a different amount of memory?
>>  
>
> Tomcat shouldn't care. I think that thread synchronization is faster
> than full context switching, but that can be very sensitive to the
> platform, OS, and tuning parameters you might have (in the OS). Java is
> perfectly happy to run with 8GB.
>
>  
>> I realize with the options I mentioned above there are implications
>> regarding high-availability and performance, but I'm not sure exactly what
>> they'd be. Perhaps someone with more knowledge of this kind of stuff could
>> comment.
>>  
>
> If you trust your operating system (I would trust any UNIX and UNIX-like
> OS, and Windows is somewhat dependable if you don't ask it to do too
> many things), then a single instance of the OS on a lot of hardware is
> just fine: go for it.
>
> If you are concerned about your OS's stability, then by all means run
> multiple instances of the OS and load balance between. From a strict
> performance standpoint, less is more, so stick to one OS and one Tomcat
> instance on that big, fat machine.
>
> - -chris
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--
------------------------------------------------------------------------
Alexey N. Solofnenko <http://trelony.cjb.net/>
Pleasant Hill, CA (GMT-8 usually)