Hey HN! Author here. We added faceted search capabilities to our `pg_search` extension for Postgres, which is built on Tantivy (Rust's answer to Lucene). This brings Elasticsearch-style faceting directly into Postgres with a 14x performance improvement over a CTE based approach by performing facet aggregations in a single BM25 index pass and making use of our columnar store.

You get the same faceting features you'd expect from a dedicated search engine while maintaining full ACID compliance. Happy to answer technical questions about the implementation!