I like lucene and have used it for many years, but sometimes a conceptually close match is what you want. Lucene and friends are fantastic about word matching, fuzzy searches, stem searches, phonetic searches, faceting and more but have nothing for conceptually or semantically close searches (I understand that they recently added new document vector searches). Also vector searches usually always return something which is not ideal in a lot of cases. I like Reciprocal Rank Fusion myself as it gives the best of both worlds. As a fun trick I use duckdb to do RRF with 5million+ documents and get low double-digit ms response time even under load