static int compareSortData(FastHit left, FastHit right, Sorting sorting) {
        if (!left.hasSortData(sorting) || !right.hasSortData(sorting)) {
            return 0; // cannot sort
        }
        return LeanHit.compareData(left.sortData, right.sortData);
    }
Sets the index of the node this hit originated at
container-search/src/main/java/com/yahoo/prelude/fastsearch/FastHit.java