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Re: Performance G4 --> G5

email@hidden wrote: 
On Tue, 28 Sep 2004, Greg Guerin wrote:


The server VM is intended for processes with long lifetimes.  It's not just
that a few routines get executed millions of times.  The process itself
typically has to run for a long enough period of time that the overhead of
performing the optimizations gets amortized.


That's exactly my point. Many people speak of the server VM as a panacea for all performance problems, and assert that nearly all programs should be run with the server VM. Based on my experience, the opposite is true. The set of programs which consistently perform better with the server VM than the client VM may be quite small. 

Maybe, maybe not.

A long running process isn't qualified just as one that has a long runtime. It typically has a mass of information that is constantly present whilst at the same time generating a lot of garbage objects with short-term lifetimes.

Also, the server vm is very aggressive in it's heap consumption so, for example, if you run the server vm with the same amount of memory as the client vm, you probably won't see improvement. And that might even contribute to the wild variations you see.

I see measurable improvement with JavaSpaces implementations (I wrote Blitz - http://www.dancres.org/blitz/index.html) and the all-java databases so long as you give them plenty of memory. I suspect web-servers with large caches of static pages or page templates will also benefit (though I've not tested these myself) as might caching technologies such as Tangosol Coherence.

In general, java programs which have these (JavaSpaces/Databases/Large Caches) execution profiles will benefit from the server vm - just how big that set of things is I don't know.

Hope that helps,

Dan.
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