WCF and n-tier architecture and serialization performance

Question

When working with 5-tier architecture (front-end => interface tier => business tier => database tier => database) using WCF service as the interface tier, having the client applications calling it's methods, should I use also WCF service for the business and database tiers? I ask because of all the serialization / deserialization that will be going on between the 3 services is probably going to consume a lot of CPU for the server, and have a performance impact on the application as a whole, or am I wrong?
In the case of running all 3 component layers on a single machine, is it better to build the business and database tiers as simple class libraries, and leave only the interface layer as WCF?
Tks

Answer 1

Tiered architecture is a pre-SOA approach, although we still build logical tiers in our software today. But physical tiers, if more than one (apart from UI and database), will cause you pain and heartache. Sometimes you end up having two but I personally advise against it.

Trend is using parallel/decoupled processing using Service Bus or similar methods and building serial services are not recommended.

You have pointed out the serialisation overhead. But that is just the beginning, you have method execution delay, more points of failure, degradation of performance since layers talk out of process, maintenance overhead, ...

So do not be apologetic about having only one middleware physical layer, that is not an asset it is a liability.

Answer 2

WCF is useful for communication between physical machines. Although you can use WCF to communicate intra-process there are simpler and more efficient ways to accomplish the same thing. You would only use WCF intra-process if you were thinking about putting the different layers on different machines at some point. As far as using WCF for the database tier, you wouldn't: you would use the classes in the System.Data.xxx namespaces (ie System.Data.SqlClient if you are using a SQL server database; or possibly the Entity Framework).

Edits:

When people talk about 3-tier architecture they are mixing two concepts into one: physical tiers: a client machine, a middleware machine and a Database machine; and logical layers in the software architecture: client UI code, Business logic code, and data access code. When code from two different logical layers that reside on the same physical machine need to communicate the simplest model is one class calling into another, the amount of decoupling depends on your requirements. You want to use the simplest model that satisfies your requirements. Rockford Lhotka has an excellent description of this in the first chapter of his book Expert C# 2008 Business Objects