Recently,peer-to-peer (P2P) search technique has become popular in the Web as an altative to centralized search due to its high scalability and low deployment-cost.However,P2P search systems are known to suffer from the problem of peer dynamics,such as frequent node join/leave and document changes,which cause serious performance degradation.This paper presents the architecture of a P2P search system that supports full-text search in an overlay network with peer dynamics.This architecture,namely HAPS,consists of two layers of peers.The upper layer is a DHT (distributed hash table) network interconnected by some super peers (which we refer to as hubs).Each hub maintains distributed data structures called search directories,which could be used to guide the query and to control the search cost.The bottom layer consists of clusters of ordinary peers (called providers),which can receive queries and ret relevant results.Extensive experimental results indicate that HAPS can perform searches effectively and efficiently.In addition,the performance comparison illustrates that HAPS outperforms a fiat structured system and a hierarchical unstructured system in the environment with peer dynamics.