JuliaLang/julia — comment on commit 0155fd0242bf1e7066bf6eeba05a3cda1a4553b0
File:  line 0
By JeffBezanson:

I do get a nice speedup from this on linux. Especially in the case of no pipes; with pipes not so much.

Now, this is silly, but it turns out avoiding writing to the heap is difficult: iterating over a hash table allocates tuples. To get rid of all the writes we might need to use an Array or move the data to an Array first.