Transactions Checkpoint

Distinguish lock protocols and trace FIFO and upgrade dependencies.

Get every question correct to pass this checkpoint. You can review feedback, revise your answers, and submit again.

1. A transaction acquires S(A), releases S(A), then acquires X(B). All grants are compatible. Does this follow basic 2PL?

Select one answer.

Yes, because shared locks do not count No, because it acquires a lock after entering the shrinking phase Yes, because it uses exactly two resources No, because 2PL prohibits exclusive locks

2. Using this lesson's terminology, which additional rule distinguishes strict 2PL from basic 2PL?

Select one answer.

No transaction may wait for a lock Every lock is obtained before the transaction begins Exclusive locks remain held until commit or completed abort All lock requests must be shared

3. T1 holds S(A), T2 waits for X(A), and T3 requests S(A). Under this exercise's FIFO policy:

Select one answer.

T3 queues behind T2 despite compatibility with T1 T3 is immediately granted because S/S is compatible T2 immediately replaces T1 as holder The three transactions necessarily form a deadlock

4. T1 and T2 hold S(A); both request upgrades to X(A). What happens?

Select one answer.

Both upgrades are granted together The second requester automatically loses its S lock No deadlock is possible with a single resource Both retain S while waiting, so a directed cycle is detected

5. T1 holds S(A), T3 holds X(B), T2 queues for X(A), T3 queues for S(A), then T1 queues for X(B). Which dependency would a holder-only graph miss?

Select one answer.

T2→T1 T3→T2 from FIFO ordering T1→T3 T1→T1 from its own lock

6. Why can the lock-manager API not independently guarantee strict 2PL?

Select one answer.

It cannot store more than one resource FIFO always violates strict 2PL It receives no transaction commit/abort lifecycle with which to enforce lock retention Directed cycle detection prevents serialization

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