Question

If I have a high-end server, for example with 1T memory and 8x4core CPU...

will it bring more performance if I run multiple App Server (on different JVM) rather than just one App Server?

On App Server I will run some services (EAR whith message driven beans) which exchange message with each other.

btw, has java 64bit now no memory limitation any more? http://java.sun.com/products/hotspot/whitepaper.html#64

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Solution

will it bring more performance if I run multiple App Server (on different JVM) rather than just one App Server?

There are several things to take into account:

  • A single app server means a single point of failure. For many applications, this is not an option and using horizontal and vertical scaling is a common configuration (i.e. multiple VMs per machine and multiple machines). And adding more machines is obviously easier/cheaper if they are small.

  • A large heap takes longer to fill so the application runs longer before a garbage collection occurs. However, a larger heap also takes longer to compact and causes garbage collection to take longer. Sizing the VM usually means finding a good compromise between frequency and duration (in other words, you don't always want to give as much RAM as possible to one VM)

So, to my experience, running multiple machines hosting multiple JVM is the usual choice (and is usually cheaper than a huge beast and gives you more flexibility).

OTHER TIPS

There is automatically a performance hit when you need to do out-of-process communications, so the question is if the application server does not scale well enough so this can pay off.

As a basic rule of thumb the JVM design allows the usage of any number of CPU's and any amount of RAM the operating system provides. The actual limits are JVM implementation specific, and you need to read the specifications very carefully before choosing to see if there is any limits relevant to you.

Given you have a JVM which can utilize the hardware, you then need an app server which can scale appropriately. A common bottleneck these days is the amount of web requests that can be processed per second - a modern server should be able to process 10000 requests per second (see http://www.kegel.com/c10k.html) but not all do.

So, first of all identify your most pressing needs (connections per second? memory usage? network bandwidth?) and use that to identify the best platform + jvm + app server combination. If you have concrete needs, vendors will usually be happy to assist you to make a sale.

Most likely you will gain by running multiple JVMs with smaller heaps instead of a single large JVM. There is a couple of reasons for this:

  1. Smaller heaps mean shorter garbage collections

  2. More JVMs means lesser competition for internal resources inside JVM such as thread pools and other synchronized access.

How many JVMs you should fit into that box depends on what the application does. The best way to determine this is to set up a load test that simulates production load and observe how the number of requests the system can handle grows with the number of added JVMs. At some point you will see that adding more JVMs does not improve throughput. That's where you should stop.

Yet, there is another consideration. It is better to have multiple physical machines rather than a single big fat box. This is reliability. Should this box go offline for some reason, it will take with it all the app servers that are running inside it. The infrastructure running many separate smaller physical machines is going to be less affected by the failure of a single machine as compared to a single box.

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