Reciprocal Rank Fusion (RRF): how it works and when to skip it

Hybrid search is commonly used in the search systems which runs several retrievers for a given same query (For ex: a keyword retriever, a dense embedding retriever) and each retriever returns its own top-k ranked list of documents. User cares about a single list and not lists of list from different retrievers, so you have to merge those lists into a single list. The most common way to merge the ranked results from different retrievers is to use Reciprocal Rank Fusion. In this post I'll walk…