Annoy

Spotify’s C++ library with Python bindings for memory-efficient approximate nearest neighbor searches in high-dimensional spaces.

Annoy (Approximate Nearest Neighbors Oh Yeah) optimizes similarity searches by building static file-based index structures that are shared across processes via mmap. This architecture allows systems to handle millions of vectors (like 100-dimensional song embeddings) without bloating RAM usage. It uses random projections to create a forest of trees, balancing search speed and accuracy through a single parameter: the number of trees. Whether you are serving music recommendations to 500 million users or clustering research data, Annoy delivers sub-millisecond lookups and a minimal memory footprint.

https://github.com/spotify/annoy