This API is designed to achieve high performance sorting, by exposing a tight interaction with FieldValueHitQueue as it visits hits. Whenever a hit is competitive, it's enrolled into a virtual slot, which is an int ranging from 0 to numHits-1. The FieldComparator is made aware of segment transitions during searching in case any internal state it's tracking needs to be recomputed during these transitions.
A comparator must define these functions:
NOTE: This API is experimental and might change in incompatible ways in the next release.