This is a summary on Chapter 21.1 Two-Phase Locking Techniques for Concurrency Control from Fundamental of Database system by Pearson 2015. The goal of this blog is to give a concrete example on how 2PL’s schedule is guaranteed to be serializable. Figure 1: Figure 21.3 Figure 2: Figure 21.4 Figure <Figure_21.3> and figure <Figure_21.4> uses the same set of locks which is provided in Shared/Exclusive locks including read_lock, write_lock and unlock.