Pitfalls of Lock-Based Protocols(Cont) he potential for deadlock exists in most locking protocols Deadlocks are a necessary evil Starvation(53t)is also possible if concurrency control manager is badly designed. For example T5 T6 T7 T8 lock-S(Q) Lock×(Q) lock-S(Q) unlock(Q) lock-S(Q) unlock(Q) unlock(Q) Database System Concepts 3rd Edition 16.7 OSilberschatz, Korth and SudarshanDatabase System Concepts 3 16.7 ©Silberschatz, Korth and Sudarshan rd Edition Pitfalls of Lock-Based Protocols (Cont.) The potential for deadlock exists in most locking protocols. Deadlocks are a necessary evil. Starvation（饿死） is also possible if concurrency control manager is badly designed. For example: T5 T6 T7 T8 lock-S(Q) Lock-X(Q) lock-S(Q) unlock(Q) lock-S(Q) unlock(Q) unlock(Q)