Which of the following concurrency control techniques ensures that transactions maintain consistency by preventing the occurrence of phenomena like dirty reads, non-repeatable reads, and phantom reads?Multiversion Concurrency Control (MVCC)Two-Phase Locking (2PL)

The Two-Phase Locking (2PL) technique ensures that transactions maintain consistency by preventing the occurrence of phenomena like dirty reads, non-repeatable reads, and phantom reads.

Here's a step-by-step explanation:

1. Two-Phase Locking (2PL) is a concurrency control method that ensures serializability in the schedule of transactions. It does this by dividing the execution of each transaction into two phases: the growing phase and the shrinking phase.

2. During the growing phase, a transaction acquires all the locks it needs and does not release any locks. This prevents other transactions from accessing the locked data, thus avoiding dirty reads (reading uncommitted data from another transaction).

3. During the shrinking phase, the transaction releases all its locks and does not acquire any new ones. This ensures that once a transaction has read a data item, no other transaction can change it until the first transaction is complete, thus preventing non-repeatable reads (reading different values of the same data item in the same transaction).

4. By ensuring that locks are held until a transaction is complete, 2PL also prevents phantom reads (reading new data items that were not originally present in the data set).

5. Therefore, by controlling when locks are acquired and released, the Two-Phase Locking (2PL) technique ensures that transactions maintain consistency and prevent the occurrence of dirty reads, non-repeatable reads, and phantom reads.