Deadlock Detection In the centralized deadlock-detection approach,a global wait-for graph is constructed and maintained in a single site;the deadlock-detection coordinator Real graph:Real,but unknown,state of the system. Constructed graph:Approximation generated by the controller during the execution of its algorithm. the global wait-for graph can be constructed when: a new edge is inserted in or removed from one of the local wait-for graphs. a number of changes have occurred in a local wait-for graph the coordinator needs to invoke cycle-detection. If the coordinator finds a cycle,it selects a victim and notifies all sites.The sites roll back the victim transaction. Database System Concepts-7th Edition 23.27 ©Silberscha乜，Korth and SudarshanDatabase System Concepts - 7 23.27 ©Silberschatz, Korth and Sudarshan th Edition Deadlock Detection ▪ In the centralized deadlock-detection approach, a global wait-for graph is constructed and maintained in a single site; the deadlock-detection coordinator • Real graph: Real, but unknown, state of the system. • Constructed graph: Approximation generated by the controller during the execution of its algorithm . ▪ the global wait-for graph can be constructed when: • a new edge is inserted in or removed from one of the local wait-for graphs. • a number of changes have occurred in a local wait-for graph. • the coordinator needs to invoke cycle-detection. ▪ If the coordinator finds a cycle, it selects a victim and notifies all sites. The sites roll back the victim transaction