: It's not really a performance-related issue, the primary goal is to use the : facet information to determine the most relevant product category related to : the particular search being performed.
ah ... ok, i understand now. the order does matter, you want the "top N" documents sorted by some criteria (either score, or maybe popularity i would imagine) and then you want to pick the categories based on that. i had to build this for CNET back before solr went open source, but yes - i did it using a custom subclass of dismax similar to what i discribed before. one thing to watch out for is that you probably want to use a consistent sort independent of the user's sort -- if the user re-sorts by price it can be disconcerting for them if that changes the navigation links. -Hoss
