Before it
Similarity search over large vector sets ran on CPU and did not scale.
The problem
Retrieval over billions of embeddings was too slow to sit inside a model's loop.
What it introduced
GPU-accelerated approximate nearest-neighbour search, released as a library.
Why it matters
The plumbing under every vector database and RAG stack. DPR and RAG both call it directly.
What modern models inherit
Fast approximate vector search as an assumed capability.
What came next
DPR and RAG used it; the commercial vector-database market grew around the same primitive.