The Two-Phase Locking Protocol (Cont.) There can be conflict serializable schedules that cannot be obtained if two-phase locking is used. However,in the absence of extra information(e.g.,ordering of access to data),two-phase locking is needed for conflict serializability in the following sense: Given a transaction T that does not follow two-phase locking,we can find a transaction T that uses two-phase locking,and a schedule for T; and T that is not conflict serializable. Database System Concepts-5th Edition,Oct 5,2006 16.10 ©Silberschat乜，Korth and SudarshanDatabase System Concepts - 5 16.10 ©Silberschatz, Korth and Sudarshan th Edition, Oct 5, 2006 The Two-Phase Locking Protocol (Cont.) There can be conflict serializable schedules that cannot be obtained if two-phase locking is used. However, in the absence of extra information (e.g., ordering of access to data), two-phase locking is needed for conflict serializability in the following sense: Given a transaction Ti that does not follow two-phase locking, we can find a transaction Tj that uses two-phase locking, and a schedule for Ti and Tj that is not conflict serializable