AI engineering glossary · RAG vector search
What is efSearch?
efSearch (also called ef): In HNSW, the size of the candidate list kept during a query. Larger values explore more of the graph, raising recall and latency together, so it is the main knob for tuning speed versus accuracy at query time.
efSearch: an example
Increasing efSearch from 50 to 200 lifts recall@10 from 92% to 98% while latency roughly doubles.
Related terms
More RAG vector search terms
- Embedding
- Embedding cache
- Embedding drift
- Exact nearest neighbour search
- FAISS
- Faithfulness
- Fixed-size chunking
- Flat index
Where you learn it
efSearch is part of the AI Engineering Program, which teaches it with notes, a hands-on lab and an exam. The first lesson is free.