HedraRAG: Co-Optimizing Generation and Retrieval for Heterogeneous RAG Workflows

In this paper, we identify and tackle emerging system-level challenges in serving heterogeneous RAG workflows, characterized by complex stages and diverse request patterns. We present HedraRAG, a new system built on RAGraph, a graph-based abstraction that exposes optimization opportunities across stage-level parallelism, intra-request similarity, and inter-request skewness. These opportunities are expressed through graph transformations, including node splitting, reordering, edge addition and rewiring. Transformations are dynamically applied to wavefronts of subgraphs across concurrent requests and scheduled onto the CPU-GPU pipeline. Experiments across a wide range of workflows demonstrate that HedraRAG achieves more that 1.5× and up to 5× speedup over existing frameworks, offering a comprehensive solution for heterogeneous RAG workload serving.