Dynamic load profiling

[jonhoo]

It'd be really cool if the system kept stats about how "busy" different parts of the graphs were. For example, how many records they're processing per second or how long they spend idle between every time they're woken up. This might help to identify performance regressions and opportunities for optimization, but could also have a wider impact by allowing the controller to re-shard or replicate nodes in response to increase/decreased load.