What RAG actually is
Retrieval-Augmented Generation (RAG) is an architecture pattern that combines a language model with a retrieval system — typically a vector database — to ground AI outputs in a specific knowledge base. Instead of relying entirely on what the language model learned during training, a RAG system retrieves relevant documents at inference time and uses them as context for the model's response. This reduces hallucination, allows the system to answer questions about information that was not in the training data, and makes the system's knowledge updatable without retraining.
When RAG is the right architecture
RAG is well-suited for use cases where the relevant knowledge is large, changes over time, and is too proprietary to include in a public model's training data. Enterprise knowledge bases, product documentation, legal and compliance documents, and internal procedure libraries are all good candidates. RAG is less suited for use cases that require reasoning over structured data — for those cases, a SQL interface or tool-using agent architecture is typically more reliable.
The retrieval quality problem
The most common failure mode for RAG systems is poor retrieval quality — the system fails to find the relevant documents, retrieves irrelevant documents, or retrieves documents that are individually relevant but collectively contradictory. The quality of RAG outputs is bounded by the quality of retrieval. This means that chunking strategy, embedding model selection, and retrieval scoring are not implementation details — they are the core of the system.
Chunking strategy
How documents are divided into chunks for indexing has an outsized impact on retrieval quality. Chunks that are too large dilute the relevance signal. Chunks that are too small lose context. Chunks that split across semantic boundaries produce incoherent retrievals. A production RAG system requires a chunking strategy tuned to the specific document types and query patterns of the use case.
Hybrid retrieval
Pure vector similarity search performs poorly for queries that contain specific identifiers — product codes, proper names, dates. Hybrid retrieval — combining dense vector search with sparse keyword search — typically outperforms either approach alone, particularly for enterprise use cases where documents contain structured identifiers alongside unstructured text.
Evaluation
RAG systems require evaluation frameworks that test the full retrieval-generation pipeline, not just the language model. Retrieval precision and recall, answer faithfulness to retrieved context, and answer relevance to the query are the primary dimensions to evaluate. Building these evaluation frameworks before beginning system development allows teams to make architecture decisions based on measured performance rather than intuition.
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