A recent interview of some Twitter developers, on Twitter’s use of Scala has touched off a fair amount of controversy in the Ruby community, and prompting Todd Hoff of the High Scalability to muse on an interesting statement: At some point, the cost of servers outweighs the cost of programmers.

We all know that the scripting languages that are frequently favored in Web development today — Ruby, Python, and PHP — do not perform as well as Java, and Java in turn can be outperformed by well-written native C/C++ code. However, these popular dynamic programming languages typically lead to better programmer productivity. The argument has been that it’s more cost-effective to have more productive developers, than it is to buy less infrastructure. There is a point, though, when that scale equation can be flipped on its head — when the cost of the servers, due to the performance sacrifices, gets too high. (I would add that you can’t look at simple hardware spend alone, either. You’ve got a infrastructure TCO to look at. It’s not just about more people to maintain more servers, either — that equation is not linear, as a sysadmin can manage more systems if they’re all identical and there are good automation tools. But systems that are struggling due to performance issues soak up operations time with daily firefighting.)

Twitter’s developers are not advocating that people abandon what they know and love, but they’re forging a new path for themselves, with an open-source language developed in academia. Scala can be compiled to either Java or .NET bytecode, allowing it to interoperate bidirectionally with Java and CLR code; this is important for driving adoption because programmers generally like to work with languages that have a solid base of libraries (i.e., someone else has conveniently done the work of producing code for commonly-needed capabilities), and because this makes it possible for Scala to leverage the existing tools community for Java and .NET. Scala’s equivalent of Rails, i.e., a convenient framework, is Lift.

Scala doesn’t have much adoption now, but it’s worth noting that the rapid pace of Web 2.0 innovation is capable of driving extremely fast uptake of things that turn out to solve real-world problems. (For comparison: Not long ago, practically no one had heard of Hadoop, either, but it’s built quite a bit of buzz now.) That’s important for anyone contemplating the long-term future of particular platforms, particularly APaaS offerings that are tied to specific programming languages. The favored platforms can and do change in a tidal fashion — just look at the Google trend graph for Ruby on Rails to see just how aggressively interest can increase over a single year (2005 to 2006).

As a coda to all of this, Twitter’s Alex Payne has a smart blog post, noting that social media fills the vacuum between peer-reviewed journals and water-cooler conversations, yet deploring the fact that in these mediums, emotion can rule over what is measurable. The takeaway — whether you’re an IT manager, a marketing manager at a vendor, or an investor — from my perspective, is this: There’s an emotional context to programming language choice. These are not merely technical communities; these are fandoms, and they form part of a developer’s self-identity.