Názor k článku Erlang: začínáme programovat od Radek Miček - Facebook přepsal chat z Erlangu do C++ -...

Facebook přepsal chat z Erlangu do C++ - viz třeba http://www.quora.com/When-did-Facebook-switch-away-from-using-Erlang-for-Facebook-Chat/answer/Ben-Maurer

At the time Facebook switched away from Erlang, the chat system had numerous reliability issues. The Erlang servers (which were used to provide long-poll functionality for browsers) caused some, but certainly not all of the problems. One problem we found with Erlang was that some of the abstractions Erlang had that allowed one to transparently have a distributed system across multiple machines actually caused reliability problems -- one server in the group would fail and cause cascading issues. Secondly, we found a number of instances where Erlang wasn't scaling well to multiple cores.

I don't think these issues are necessarily fundamental flaws of the Erlang runtime. It's quite possible that there was tuning that would have made Erlang work better for us (in fact, in our investigations we found a few tuning options that helped us).

However, Facebook has a number of useful abstractions in C++, making that a logical replacement.