Hello Guix!

Every time a package changes, we end up downloading complete substitutes
for itself and for all its dependents, even though we have the intuition
that a large fraction of the files in those store items are unchanged.

I wanted to evaluate that by looking at store items corresponding to
subsequent revisions of a package (be it different versions or rebuilds
induced by dependencies), and this is what the program below does.

Here are preliminary results for a few packages: