[wrboyce]

Maybe I am missing something, but aren't separate heaps (i.e., no shared memory between processes) one of the things that makes concurrency such a "joy" in Erlang?

Why do you feel the major selling point was the first big mistake?

[EvanMiller]

Well, technically there is a difference between separate heaps and no shared memory. Data in Erlang is immutable, so processes could use a combined heap, but they still wouldn't have read-write shared memory.

However, in my opinion separate heaps was absolutely 100% the correct design decision. The main benefit is not having to worry about the effects of a long-running, stop-the-world garbage collection, which can have catastrophic effects on user interaction, server response times, request queue lengths, etc. An additional benefit is that the language implementers can use "dumb" algorithms for garbage collection and avoid a large class of difficult-to-track bugs.

Robert Virding talked about these issues at some length at this year's Erlang Factory; hopefully the video will be posted soon.