How And Why We Switched from Erlang to Python (2011)

The main difference is that eventlet can’t influence the Python runtime, but actors are built into Erlang at a language level, so the Erlang VM can do some cool stuff like mapping actors to kernel threads (one per core) and preemption. It might not sound “cool” to implement a data structure this way, but I was able to provide some important operations in constant time along with other optimizations that were cripplingly slow in the Erlang version. I went into Mixpanel thinking Erlang was a really cool and fast language, but after spending a significant amount of time sorting through a real implementation, I understand how important code clarity and maintainability is.

Source: engineering.mixpanel.com