Large language models (LLMs) have demonstrated great success in various fields, benefiting from their huge amount of parameters that store knowledge. However, LLMs still suffer from several key issues, such as hallucination problems, knowledge update issues, and lacking domain-specific expertise. The appearance of retrieval-augmented generation (RAG), which leverages an external knowledge database to augment LLMs, makes up those drawbacks of LLMs. This paper reviews all significant techniques of RAG, especially in the retriever and the retrieval fusions. Besides, tutorial codes are provided for implementing the representative techniques in RAG. This paper further discusses the RAG training, including RAG with/without datastore update. Then, we introduce the application of RAG in representative natural language processing tasks and industrial scenarios. Finally, this paper discusses the future directions and challenges of RAG for promoting its development.

大型语言模型和检索增强生成技术在各个领域取得巨大成功，但仍存在幻觉问题、知识更新问题和缺乏领域专长等关键问题。本文回顾了检索增强生成技术的显著技术，特别是在检索器和检索融合方面，并提供了教程代码以实现这些代表性技术。此外，本文讨论了检索增强生成技术的训练方法和应用，并探讨了其未来发展方向和挑战。

自然语言处理中检索增强的生成模型：综述