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From Christopher Schultz <ch...@christopherschultz.net>
Subject Re: Tomcat with 8 GB memory
Date Thu, 26 Jul 2007 18:56:22 GMT
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Joe,

Joe Nathan wrote:
> I would discourage to use such machine! 8GB means you are using 64 bit
> machine which will be much slower than 32 bit machines.

Huh? Why would a 64-bit machine run slower than a 32-bit machine? Even
better: why would either outperform the other when you haven't said what
you're doing? For instance, a 32-bit machine trying to run 64-bit
operations is hideously slow. A 64-bit machine running 32-bit operations
should be just as fast as its 32-bit cousin, since it's getting no
advantage with those wasted 32 extra bits per integer.

I can't think of a single reason why a 64-bit processor would perform
worse than a comparable 32-bit processor running the same code. The
advantage of a 64-bit processor is access to more (flat) memory and it
can do bigger operations with less scratch work.

With comparable hardware, I would expect a 64-bit JVM (on 64-bit HW) to
perform identically to a 32-bit JVM (on 32-bit HW) when running the same
application (assuming that no heavy mathematical calculations are being
done that could benefit from 64-bit capability).

> Big memory is useful
> ONLY if you have applications that can benefit big memory such as database
> systems. In Java, if you use lots of memory and create lots of objects, your
> Java applications will have periodic [seizures]!

Hm. I don't think JVMs have used stop-the-world GC for some time, now.

> This is because of garbage
> collection will take significant time, if started. 

Full GCs happen very rarely, unless you are abusing your heap.

> I would be happy with 1 ~ 2 GB 32bit machines! This could deliver much
> faster services.

While a fleet of 2GB commodity boxes do have their advantages, you don't
have to set up complicated load balancing if you've got one huge machine
that can do everything ;)

- -chris

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