See here. _indexKeyCount stores map of hashed KeyString values to count. We increment this count for each key found while scanning a collection and decrement for each key we find in an associated index. We then expect the final count to be 0 if consistent, > 0 if the collection has a greater number of entries and < 0 if the index has a greater number of entries. Given this we should store the count in a signed integer rather than the current uint32_t.