Question

In class, we discussed strict two-phase locking which is two-phase locking with the added constraint that all locks must be released at the end of the transaction and a transaction acquires locks immediately before it first accesses a database item. Suppose you remove these added constraints (so locks can be released earlier than the end of the transaction provided no new locks are acquired afterward and locks may be obtained way before they are needed), giving “pure” two-phase locking.

An execution is order-preserving serializable if it is serializable and the following holds: whenever all operations of some transaction T1 precede all operations of some other transaction T2 (i.e. whenever T1 completes before T2 begins), then there exists an equivalent serial execution in which T 1 precedes T 2. Prove that pure two-phase locking produces order-preserving serializable executions.

Answer 1