In a large system like Twitter you're not going to micro-optimise every line of code. You want a good performance baseline and the ability of quickly write corr

In a large system like Twitter you're not going to micro-optimise every line of code. You want a good performance baseline and the ability of quickly write correct code. For many Scala and the JVM is a better tradeoff than C or C++ in this regard. See Martin Thompson's blog if you want to know more about low-level performance optimisation on the JVM. You're also overlooking the benefit of a modern type system. If you haven't used one before it's difficult to appreciate what they bring. Twitter's Summingbird project is a great example of how a few powerful abstractions, enabled by Scala's type system, can simplify a very complex problem. What I like about Scala and the JVM is they have a large expressive width (http://noelwelsh.com/programming/2013/07/10/expressive-width/ http://noelwelsh.com/programming/2013/07/10/expressive-width...). I can write very terse, expressive code when productivity is the main focus, but also reach down to grub around with low-level code if I need to squeeze out performance. Very few platforms offer this.