scanIndex merged each further record of an already-seen category with
mergeAttributes, which rebuilt a map and re-sorted every attribute the
category had so far. A category with A attributes split over N records
cost A*N, about an hour and a half for a 5 MB file, while the scan lock
was held and every geodata route waited on it.
Each category now collects its attributes in one set during the walk,
and the sorted lists are built once at the end.
MHSanaei
2024d34928