Structure Is All You Need to Reuse: Accelerating GraphRAG via Meta-Structure-Aware KV Caching
Retrieval-Augmented Generation over Knowledge Graphs (GraphRAG) enhances Large Language Models (LLMs) with structured, multi-hop evidence. However, existing GraphRAG systems predominantly linearize retrieved subgraphs into long textual prompts, forcing LLMs to recompute identical schema-level reasoning across queries repeatedly. This text-centric design incurs substantial prefilling latency, memory overhead, and severely limited cache reuse under entity-level variations. We observe that although retrieved entities differ across queries, their underlying logical schemas (meta-structures) recur with high frequency, indicating that most computational cost is spent on repeatedly encoding invariant structural logic. In this paper, we propose MetaKV, the first structure-aware KV caching mechanism that explicitly decouples static structural logic from dynamic entity semantics in GraphRAG inference. In a preparation phase, MetaKV mines frequent meta-structures and pre-computes their Key-Value (KV) caches as reusable Skeleton KVs. During inference, query-specific entity representations are injected into reserved structural slots to assemble the context without recomputing graph topology. To further enforce faithfulness to graph reasoning, MetaKV introduces a Topological Mask that constrains attention to valid graph edges. Extensive experiments conducted on HotpotQA and MetaQA datasets demonstrate that MetaKV achieves up to 6.4× prefilling speedup and a 73% effective cache-hit rate while maintaining competitive reasoning accuracy, enabling high-throughput, low-latency GraphRAG without sacrificing adherence to graph topology.