OpenSearch

Amazon OpenSearch Service is a managed search and analytics engine built on the open-source OpenSearch project. In generative AI it acts as a vector store, indexing high-dimensional embeddings and running k-nearest-neighbor (k-NN) queries to retrieve semantically similar documents — the core retrieval step in a RAG pipeline. Amazon Bedrock Knowledge Bases can use OpenSearch Serverless as a fully managed, auto-scaling vector backend, removing the need to provision or tune cluster capacity. The key exam distinction versus a dedicated vector store like Aurora PostgreSQL with pgvector or Pinecone: OpenSearch combines dense vector search with traditional keyword (BM25) search in one engine, enabling hybrid retrieval. When a question asks which AWS-native service supports both lexical and semantic search together, OpenSearch is the answer.