All event processing (currently) takes place on three 32 core Xeon machines. But it has seen much worse days when we had many more before we optimized critical paths. Likewise what we have now is pretty chill, but we need to also consider the case where a worker drops entirely from the pool so these are over-provisioned for the amount of work they each take.

The data layer is probably more interesting from a scaling point of view in general since it's harder to scale, but it's also not exactly a point we're particularly happy with. There is already a comment from david (zeeg) on this post going into our plans there.