10.6 Scalability

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There is a lot of confusion about scalability and application performance and many people confuse the two issues.

I have worked on many applications that were extremely fast. They performed exceptionally well, and the user was very happy that he or she could process so many widgets per hour so quickly using this wonderful new software. Then the business started to grow and more people were hired to work on the system; very soon the widget processing rate started to tumble since the solution could not scale to cope with more than five users.

Scalability has been brought into the spotlight with the advent of the Internet as a mainstream business tool. Alongside security, it must rate as one of the most important issues for Web site designers, and with the average user only being prepared to wait 20 seconds for a page to load, the implications for a poorly scaling site can be huge.

.NET is now introducing the idea of Web services (see Chapter 9) as a way to develop and deliver megaservices-that is, Web-based services designed to run 24x7 with no downtime. Alongside these services there is a whole new industry being developed for lawyers to write onerous servicelevel agreement contracts that guarantee a level of performance (really scalability) from each of these services. I guess, quite rightly, that your business can be at risk if an important Web service your customers use should fail through no fault of your own.

Scale up or Scale out

Microsoft has the benefit of hedging its bets on scalability, offering both a scale-out and a scale-up solution.

• Scale up . This is the solution that vendors of huge servers really enjoy. It basically means installing and configuring the largest possible multiprocessor server you can find and cramming it full of huge amounts of memory. The advantage is that you only have one box to manage, but the disadvantage is that you have one point of failure, and it is possibly very costly.

• Scale out . This appeals to PC enthusiasts since it uses commodity PC servers but networks them together to provide a large virtual server. The downside of scaling out is the need to have a set of management tools capable of running such a configuration, but the upside is that you can easily add additional hardware or, if the going gets tough, take hardware away!

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