Do all of the rankings need the same precision? Maybe you can get away with perfect accuracy for the top 1,000 rankings and then provide an approximation for a

Do all of the rankings need the same precision? Maybe you can get away with perfect accuracy for the top 1,000 rankings and then provide an approximation for anything >1,000? You could use a list for the first 1,000 and then store the rest in a tree. Then have another process that walks the tree in-order and updates the ranking of each node.