Most of the reasoning is documented in the big comment. In short, we tried
to solve the problem with caching, but the caching should hardly be necessary
now that the bottleneck should be fixed. We'll see on production if it
actually solves the whole problem, but I've confirmed in the console that
redefining this function makes random_basic_per_species (as called during
rendering) a ton faster. And this way we keep our randomness, woo!
items#show has been very slow recently, and I think it's because there's a lot
of querying to be done. Another option would have been to attempt to
short-circuit Item#supported_species if not body specific, but that would
still leave us with 1s load times for body specific items, which is not
satisfactory. The short-circuiting might still be worth doing, but probably
not now.
I'm also not sure that this is actually the core performance problem, but
we'll see. It definitely helped on the dev server: items#show took about
200ms on item pages where everything but species images were cached, then
took about 30ms on subsequent loads. Looking like a good candidate.
