Never. Use PyPy if you need to speed up your servers (note the caveats regarding C extensions, if you have any being used).

Celery needs help badly. I'm one of the maintainers and we're swamped with issues to triage, bugs to fix etc.

Yeh I know. We discussed this approach on the #PyPy irc channel. As far as I recall the wrapper is not open source. We needed something that can be done quickly and therefore Reflex code generation based approach worked better for us.

there is no wrapper ;-) at least no wrapper generator, we just hand-wrapped some stuff.

Reflex generates the bindings for us. That's why we chose it instead of hand-wrapping the C API ourselves.

I fixed the link to reflex. Thanks for that.

I can extend the explanation about cppyy/Reflex if needed.

To my best understanding, the pure Python implementation is much slower. Even on PyPy.

I did not know that Protobuf 3 is compatible with Protobuf 2.

I read that as Protobuf 3.0 supports proto2, which is different than proto3 being compatible with proto2.