I have read in various blogs that WCF has a scalability problem with servicing a large number of concurrent async requests for an async WCF method. Is this still true today in .Net 4.0 and IIS 7 world?
By async method in WCF, I mean that async pattern has been implemented for this WCf method.
I checked this link: WCF Scalability Issues with Async Pattern Method
WCF not scaling was never true. What was true was that applications did not scale. (And this is still true, of course).
Honestly, when did you ever see a language or framework that did not scale? Requests are independent, meaning that they are embarrassingly parallel. This is a perfect situation for scaling.
The thing that impedes scaling is always the application. It happens when the app is either not written for high-scale or the code is of low quality.
To put it concretely: If you use WCF the way it is meant to be used, and go all the way async, you’ll scale up to the hardware limits.