Leases (Cont.) Coordinator must check that it still has lease when performing action Due to delay between check and action,must check that expiry is at least some time t'into the future t'includes delay in processing and maximum network delay Old messages must be ignored Leases depend on clock synchronization Database System Concepts-7th Edition 23.33 ©Silberscha乜，Korth and SudarshanDatabase System Concepts - 7 23.33 ©Silberschatz, Korth and Sudarshan th Edition Leases (Cont.) ▪ Coordinator must check that it still has lease when performing action • Due to delay between check and action, must check that expiry is at least some time t’ into the future ▪ t’ includes delay in processing and maximum network delay ▪ Old messages must be ignored ▪ Leases depend on clock synchronization