Thread:Extension talk:DynamicPageList (Wikimedia)/Request: Uncap the number of categories you can filter/reply (4)

Actually it may not be that bad. While the cost of intersecting 2 large (mostly distinct) categories is probably O(n*log(n)), once the first two have been done you have a small set (which will only get smaller) so the cost of the next m categories is about m * n. If m is limited this can be considered O(n). Of course it may require something smarter than a generated SQL INTERSECT everything to avoid loading all categories at the same time.