Jon Udell wrote in Infoworld this week:

In the end, scalability isn’t an inherent property of programming languages, application servers, or even databases. It arises from the artful combination of ingredients into an effective solution. There’s no single recipe. No matter how mighty your database, for example, it can become a bottleneck when used inappropriately.

It’s tempting to conclude that the decentralized, loosely coupled Web architecture is intrinsically scalable.

Not so. We’ve simply learned — and are still learning — how to mix those ingredients properly. Formats and protocols that people can read and write enhance scalability along the human axis. Caching and load-balancing techniques help us with bandwidth and availability.

But some kinds of problems will always require a different mix of ingredients. Microsoft has consolidated its internal business applications, for example, onto a single instance of SAP. In this case, the successful architecture is centralized and tightly coupled.

For any technology, the statement “X doesn’t scale” is a myth. The reality is that there are ways X can be made to scale and ways to screw up trying. Understanding the possibilities and avoiding the pitfalls requires experience that doesn’t (yet) come in a box.

Decentralization is not a hammer that can hit every nail. Experience is still the mother of good judgment.