Twitter got a 10x reduction in number of front-end web servers and a 10x latency improvement by changing the platform. The layer literally called thrift services and made HTML pages. The 10x reduction in servers was great at the scale that they were at but the 10x decrease in latency was the real winner and it had nothing to do with scale. Pure single request performance.
I think you're asking whether they optimized the rewrite, rather than just ported it from Ruby to Scala? I too would be interested to know if there is any data to this.
It was an exact port including bugs — output needed to be exactly the same as that was the best way to test the result. I wouldn't say the Scala code was any more optimized than the Ruby code was over the years. In fact, lots more effort had been put against optimizing the Ruby side (for example, the template engine was written in C for performance).
