By "the part that actually retrieves the results and ranks them" you mean the nodes of a cluster, that run the RPCs? I guess the "hotspot" would be the code th

By "the part that actually retrieves the results and ranks them" you mean the nodes of a cluster, that run the RPCs? I guess the "hotspot" would be the code that has to merge the top results from the different nodes and actually deliver top rated 10 items to the user?