DefaultPromoter promotes if the given key QPS is higher than the QPS of the least recently accessed element in the hotcache.

HCStats keeps track of the size, capacity, and coldest/hottest elements in the hot cache.

ProbabilisticPromoter promotes based on a 1/ProbDenominator chance.

Stats contains both the KeyQPS and a pointer to the galaxy-wide HCStats.

Interface is the interface for determining whether a key/value pair should be added to the hot cache.

Func implements Promoter with a function.