> Is it a common use case to load big data and then fork to use preloaded data?

A lot of the "big data" in question here is simply lots of Python module/class/code objects resulting from importing lots of Python modules.

And yes, this "pre-fork" model is extremely common for serving Python web applications; it is the way most Python web application servers work. We already have an example in this thread of another large Python web application (YouTube) that had similar needs and considered a similar approach.