I worked in a search engine :D In short, we needed to approximate the count. We had some kind of hard limit for matching documents during a regular keyword se

I worked in a search engine :D In short, we needed to approximate the count. We had some kind of hard limit for matching documents during a regular keyword search (80k maybe? It's been years since I worked there). The ranking was done after this, as well as the aggregation of data for the facets. So if your query of "cute bunnies" (faceted on file type) filled up all 80k results by the time the query processor made it through 25% of the data, and those 80k results contained 5k gifs, then we'd display '20k' next to the 'gifs' check box.