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NX: scalability?

 
Simon Ingram
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Hi there ranchers,
A simple question. What does scalability mean in the context of Java design. I hear the word in connection with performance, but have not encountered a definition so far. Any brave soul want to play dictionary?
best wishes
Simon
 
Michael Couck
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Hi Simon,
Scalability normally refers to the ability of an applicatoin to take on more clients. For example you have a web application that runs on Apache server (I am assuming you know what a web server is), the server is on a machine that can handle 10 000 concurrent clients. Your site gets very popular and 100 000 clients start accessing your web application, the server will start sending unavailable messages because it just can't handle the connections. You cant add more servers because you haven't designed the code with scalability in mind. In this case the application is not scaleble because you are running a web application on a stand alone server. The code that you write for the application will also come into contention when trying to run this for more clients. If you change your web application to a J2EE application, where the functionality is defined in EJB's for exmple, you can have several servers running the web application, and several servers running the EJB's, this would be scalable, because you could just add more servers and support more clients.
In the context of the SCJD specifications, scalability is beyond the scope really. You could incorperate this functionality but I would say it is going to take a lot longer to do this, on the other hand it would be a great learning curve. What you would want to do is to be able to load balance several servers running on different machines. Simple as that really. Maintaining the sessions of each client. Then again why bother, there are several servers that do this so why reinvent the wheel again unless you have a sadisticly inquisitive nature.
See ya
Michael
SCJD
 
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