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Let's say I'm running a cluster with two Weblogic server nodes on two servers (Solaris, 4 CPUs, 64 GB RAM each). The heap size is maxed out on these nodes and so each server runs with 40+ GB of free memory most of the time and each server usually has on average 30% CPU utilization.

Assuming that the application scales horizontally properly, does it make sense to add more application server nodes on the same hardware to take advantage of underutilized resources? The 2 GB JVM heap limit really limits the maximum number of requests that can be served by one node, right?

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This might be a little OT, but if your server has 64 GB of RAM, then you have to be running a 64-bit OS, right? And if that's the case, you should be able to use a heap size that is larger than 2 GB. For example, it's very common to run 4 GB heaps on a 64-bit OS, and I've heard of apps using 16 GB heaps. – Tom Purl Jul 8 '11 at 14:31
up vote 2 down vote accepted

I'm not all that familiar with Solaris, but I'd venture to guess that these are 32 bit machines? I believe that would be the only thing limiting the JVM to a 2GB heap size. If you upgraded these to a 64-bit OS, then you wouldn't have this limitation.

Alternatively, (and I'm not sure this is even possible with Weblogic) you could run multiple instances of it on each of your servers. That would allow each instance of Weblogic to use its 2GB of memory. With this approach, you'd likely find CPU to be the scaling bottleneck as opposed to RAM.

Oh, and to answer your question directly, no, I think it would be silly to add another cluster node at this point. Your existing nodes are barely being used. Figure out how to get around the 2GB limit and get better utilization of your existing hardware before considering the purchase of additional gear.

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Actually what I was asking is would it make sense to add another instance of Weblogic on the existing hardware as opposed to adding another physical box. Clearly I have plenty of CPU overhead, but I was wondering if there are any other possible limitations - threading, configuration issues, etc. The long term plan is to go to 64 bit but that's not feasible at this time. – Ken Liu Sep 26 '10 at 0:54
Oh, I didn't understand that at all from your question. Yes, I think it would make a lot of sense to add another Weblogic instance. Good luck! – EEAA Sep 26 '10 at 1:05

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