I have seen thwackers asking how do we get to know which OID's are being accessed by NPM , how does it calculate cpu, memory etc etc. I have as well seen a couple of questions like "we just upgraded our NPM and we see a sudden spike in memory on our Linux boxes (when you see a sudden spike then defn you would be able to figure out why )" - you would find the answers right here -> Poller Checker Tool