Question

 Consider the transactions:

T₁: R₁(A), W₁(B)

and

T₂: R₂(A), W₂(A), W₂(B)

Suppose we insert a pair of lock and unlock commands for each element of the database that the transactions can access.

• Explain how many concurrent execution schedules, of the two transactions, follow the 2PL protocol.
• Explain whether there are any serializable schedules of concurrent execution of the two transactions that do not follow the 2PL protocol.

Answer 1

The transaction processor provides concurrent access to data and supports resilience (i.e., data integrity after a system failure) by executing transactions correctly