Retrieval-Augmented Generation for Large Language Models: A Survey
Yunfan GaoYun XiongXinyu GaoKang-Xiang JiaJin PanYuxi BiYi DaiJiawei SunQian-Yu GuoMeng Wang
Synthesizes the architectural progression of retrieval-augmented generation across naive, advanced, and modular paradigms, providing a clear taxonomy of retrieval, generation, and evaluation methods designed to mitigate hallucinations in large language models.
Retrieval-Augmented Generation (RAG) has emerged as a practical way to strengthen large language models by pulling relevant external information at inference time, thereby reducing hallucinations, supplying up-to-date facts, and supporting knowledge-intensive tasks where the models’ parametric memory alone falls short.
The survey maps the rapid evolution of RAG research since the arrival of ChatGPT, organizes more than one hundred studies into three successive paradigms—Naive, Advanced, and Modular RAG—and examines the core technical components of retrieval, generation, and augmentation, together with evaluation practices and open challenges.
Across these studies the authors show that targeted pre- and post-retrieval optimizations, modular pipeline designs, and tighter integration with fine-tuning consistently raise retrieval precision and answer quality; that RAG outperforms unsupervised fine-tuning on both familiar and novel factual questions; and that adaptive or iterative retrieval patterns further improve performance on multi-step reasoning tasks while lowering unnecessary context length.
These gains matter because they allow organizations to deploy LLMs in domains that require current or proprietary knowledge without retraining the entire model, while preserving traceability to source documents and lowering the risk of unsupported output.
The survey recommends combining RAG with selective fine-tuning or lightweight adapters, extending the approach to multimodal data, and developing more robust benchmarks that test noise tolerance, negative rejection, and counterfactual robustness. It also calls for production-oriented work on latency, data security, and evaluation tooling.
The analysis rests on a broad but still rapidly changing literature; quantitative comparisons across paradigms remain limited, and many reported gains depend on specific datasets or model scales whose generalizability is not yet fully established.
- Paper: Retrieval-Augmented Generation for Knowledge-Intensive NLP Tasks, Patrick Lewis et al. (2020). This seminal 2020 paper established the foundational RAG paradigm that the source survey comprehensively classifies, reviews, and analyzes.
- Paper: REALM: Retrieval-Augmented Language Model Pre-Training, Kelvin Guu et al. (2020). REALM pioneered joint retriever-generator pre-training, serving as a vital technical precursor examined within the survey's discussion of retrieval paradigms.
- Paper: Improving language models by retrieving from trillions of tokens, Sebastian Borgeaud et al. (2022). RETRO introduced multi-trillion-token retrieval for language models, providing a cornerstone architecture evaluated in the survey's taxonomy.
- Paper: Self-RAG: Learning to Retrieve, Generate, and Critique through Self-Reflection, Akari Asai et al. (2024). Extends the survey's modular RAG concepts by introducing Self-RAG, which teaches models to autonomously critique retrieval and generation through self-reflection.
- Paper: Ragas: Automated Evaluation of Retrieval Augmented Generation, Shahul Es et al. (2024). Builds directly on the survey's evaluation frameworks by introducing Ragas, a dedicated automated evaluation suite for scoring RAG faithfulness and relevance.
- Paper: Active Retrieval Augmented Generation, Zhengbao Jiang et al. (2023). Extends traditional static retrieval discussed in the survey with FLARE, an active inference-time method where models dynamically trigger retrieval based on uncertainty.
