tl;dr: Pg_vectorsearch is an alpha-stage PostgreSQL extension providing PRISM, an IVF-style ANN index that uses RaBitQ quantization, hierarchical centroid routing, and SIMD-optimized distance computation to outperform pgvector's IVFFlat and HNSW on both query and build times (reportedly faster than HNSW at equivalent recall on 100M vectors with a quarter of the memory). It's compatible with existing pgvector `vector` and `halfvec` columns, so it can be installed alongside pgvector without rewriting data or queries. Requires PostgreSQL 18+ and offers native `vec32`/`vec16` types for new deployments.