MagLev and distributed VMs

Avi Bryant is working on MagLev, a Ruby interpreter, based on Gemstone’s Smalltalk VM, with some very amazing features, like transactioned objects distributed across several VMs:

The integrated VMs, cache, and storage conspire to create an illusion that global state is shared across all instances: no matter how many VMs you add, over however many machines, they all see and work with the same set of Ruby objects.

My geek side finds this highly exciting, and eager to see it released to see how people will deal with it in practice.

At the same time, my let’s-build-stable-and-maintainable-software side is a bit skeptic. As Joe Armstrong puts so enthusiastically, shared state is hard to manage correctly, global transactions reduce scalability, and transparent RPC is seductive, but dangerous.

I’m also curious about the speed gains pointed out. It’s well known that the Ruby VM isn’t very fast, which means that there must be opportunities for speedups. Even then, 100x faster is impressive, and history shows that sometimes the significant improvements are harder when the semantics are precisely the same. Let’s hope Avi can manage to run the Ruby tests successfully.

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