A simple way to implement fast pagination is to set item.idx whenever you insert an item into a collection. It starts at 0 and gets incremented each time. From

A simple way to implement fast pagination is to set item.idx whenever you insert an item into a collection. It starts at 0 and gets incremented each time. From there, given the number of items per page, you can trivially determine which items to display given a page number or which page to display given an item.idx. And the query uses the efficient WHERE. Of course, the last_seen pagination is only usable for pagination where users aren't deep linking into pages (like HN).