Combining Strengths
No single retrieval method is perfect. **Ensemble Retrieval** combines the results of multiple retrievers--typically a keyword-based retriever (like BM25) and a semantic vector retriever. This ensures the agent finds documents that match exact keywords while also catching broad semantic meanings.
Reciprocal Rank Fusion
LangChain uses algorithms like **Reciprocal Rank Fusion (RRF)** to merge the results from different retrievers into a single, optimized list. This hybrid approach is widely considered the state-of-the-art for production RAG systems, providing the highest possible retrieval coverage and precision for complex queries.
Conclusion
Diversity drives quality. By mastering ensemble retrieval in LangChain, you build a robust and versatile intelligence layer that can handle the full spectrum of user queries with the highest possible degree of success.