Distributed Lock Manager In the distributed lock-manager approach,functionality of locking is implemented by lock managers at each site Lock managers control access to local data items Locking is performed separately on each site accessed by transaction Every replica must be locked and updated But special protocols may be used for replicas (more on this later) Advantage:work is distributed and can be made robust to failures Disadvantage: Possibility of a global deadlock without local deadlock at any single site Lock managers must cooperate for deadlock detection Database System Concepts-7th Edition 23.25 ©Silberscha乜，Korth and SudarshanDatabase System Concepts - 7 23.25 ©Silberschatz, Korth and Sudarshan th Edition Distributed Lock Manager ▪ In the distributed lock-manager approach, functionality of locking is implemented by lock managers at each site • Lock managers control access to local data items • Locking is performed separately on each site accessed by transaction ▪ Every replica must be locked and updated ▪ But special protocols may be used for replicas (more on this later) ▪ Advantage: work is distributed and can be made robust to failures ▪ Disadvantage: • Possibility of a global deadlock without local deadlock at any single site • Lock managers must cooperate for deadlock detection