retrieval

Candidate generation's workhorse is the two-tower model: one network embeds users, another embeds items, and relevance becomes a dot product in shared space. This lesson traces the idea from collaborative filtering through matrix factorization to trained towers, why the towers must never mix features, and the cold-start problem geometry alone cannot solve.

A recommender has milliseconds to pick ten items from millions, and no model good enough to rank them all is cheap enough to run on them all. The industry's answer is a funnel: cheap candidate generation cuts millions to hundreds, an expensive ranker orders those hundreds. This lesson builds that architecture, its latency arithmetic, and the multi-source retrieval layer real systems run.

Every feed has the same impossible job: pick ten items out of millions, in under a tenth of a second. The answer is a funnel. Learn why recommenders split into a cheap retrieval stage and an expensive ranking stage, how two-tower models make retrieval possible, and why nearest-neighbour search is the trick that makes the whole thing fit in a budget.

Learn how to systematically evaluate Retrieval-Augmented Generation systems in production using RAGAS, TruLens, and Phoenix — covering golden sets, retrieval drift, embedding drift, and cost-aware eval scheduling.

A rigorous guide to measuring RAG quality using RAGAS metrics — faithfulness, answer relevancy, context precision, and context recall — plus how to build a golden dataset and recognize where automated metrics fall short.

Go beyond naive RAG pipelines. Learn how Self-RAG, Corrective RAG, and retrieval-as-tool patterns let an LLM decide when, what, and how many times to retrieve — enabling reliable multi-hop reasoning over complex knowledge bases.

Master four advanced query rewriting techniques that dramatically improve RAG retrieval quality: Hypothetical Document Embeddings, multi-query expansion, query decomposition, and step-back prompting. Learn when to reach for each and how to implement them.

Build a production-grade retrieval pipeline combining BM25 keyword search with dense vector search, then sharpen precision with cross-encoder rerankers (Cohere Rerank, Voyage rerank-2, BGE). Learn when each layer matters and how to wire them together.

A deep dive into how you split documents for retrieval-augmented generation — fixed-size, recursive, semantic, hierarchical, and late chunking — with concrete trade-offs and code for each approach.