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Java has an odd definition of "server"

August 4th, 2008 (04:03 pm)

I'm reading through the features Java added in 1.5, and I spotted something a little surprising. At least since 1.4 (1.3?), Sun's JVM has had a "server mode", in which it takes longer to start up, but then runs faster—the theory being that, if you're running a long-lived server, the tradeoff is worth it. Prior to 1.4, the default was client mode; if you wanted server mode, you had to specify "-server" at startup.

In 1.5, they added logic to infer whether you wanted server mode based on the type of machine you were on. If you're running on a 64-bit CPU, or if you're on a Unix machine with at least 2 CPUs and at least 2GB of RAM, then it's assumed that you're a server, and server mode becomes the default; if you want client mode, you have to specify "-client".

This means that every machine I might run Java on is classified as a server. My desktop machines (home and work) are 64-bit, and my laptop has 2 cores and 2GB of RAM. (Granted, I just upgraded to 2GB a week ago; but it was an option when I bought it in 2006.) I don't run much Java, but I think it's safe to say that none of what I would run is likely to be a long-lived server process.

(I suppose this would've been useful back when I was stuck using Eclipse for my compilers class; that was definitely long-lived.)


Posted by: goldsquare (goldsquare)
Posted at: August 5th, 2008 02:23 pm (UTC)

It was added in 1.2, with the JIT compiler.

Honestly, any program that is going to run with any real duration, should be in "server" mode. The nomenclature is poor. There is "fast start and bad caching" mode, and "slow start and good caching" mode. :-)

Posted by: Justin du Coeur (jducoeur)
Posted at: August 13th, 2008 05:57 pm (UTC)

Oh, I dunno. It's true that it doesn't match your environment, but I suspect those heuristics are awfully solid in terms of real-world averages -- you're not exactly typical. The 64-bit filter is likely to stop being useful soon, but up until now that formula probably got about 90% of the machines out there right...

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