Transaction System Processes(Cont.) Shared memory contains shared data Buffer pool Lock table Log buffer Cached query plans(reused if same query submitted again) All database processes can access shared memory To ensure that no two processes are accessing the same data structure at the same time,databases systems implement mutual exclusion using either Operating system semaphores Atomic instructions such as test-and-set To avoid overhead of interprocess communication for lock request/grant,each database process operates directly on the lock table instead of sending requests to lock manager process Lock manager process still used for deadlock detection Database System Concepts-5th Edition,Oct 5,2006 20.13 ©Silberschat乜，Korth and SudarshanDatabase System Concepts - 5 20.13 ©Silberschatz, Korth and Sudarshan th Edition, Oct 5, 2006 Transaction System Processes (Cont.) Shared memory contains shared data Buffer pool Lock table Log buffer Cached query plans (reused if same query submitted again) All database processes can access shared memory To ensure that no two processes are accessing the same data structure at the same time, databases systems implement mutual exclusion using either Operating system semaphores Atomic instructions such as test-and-set To avoid overhead of interprocess communication for lock request/grant, each database process operates directly on the lock table instead of sending requests to lock manager process Lock manager process still used for deadlock detection