If I recall correctly, Google switched their crawler from Python to C++ for performance and for library compatibility etc. And eBay moved the whole website from C++ to Java in 2002.
IMO, the problem is that Twitter was Ruby's poster while both were still in ascension (might as well say they still are).
The first migration they did was porting their message queue from Ruby to Scala. As mentioned on a TheGuardian article, they migrated because Starling was crashing too often and dropping tweets, so they had to stop the site and migrate manually. Also, another member claimed performance problems on some blog posts. However, Starling doesn't perform that well to Ruby standards either, so it's very difficult to say.
I'd say the migration was for "social" reasons. The team is clearly waaaay more comfortable and enthusiastic about Scala, also they seem to prefer Static typing, so using it is the best choice indeed...
IMO, the problem is that Twitter was Ruby's poster while both were still in ascension (might as well say they still are).
The first migration they did was porting their message queue from Ruby to Scala. As mentioned on a TheGuardian article, they migrated because Starling was crashing too often and dropping tweets, so they had to stop the site and migrate manually. Also, another member claimed performance problems on some blog posts. However, Starling doesn't perform that well to Ruby standards either, so it's very difficult to say.
I'd say the migration was for "social" reasons. The team is clearly waaaay more comfortable and enthusiastic about Scala, also they seem to prefer Static typing, so using it is the best choice indeed...