Database Transactions and Concurrency Control

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1. 1

   Which ACID property ensures that a transaction's operations either all succeed or all have their effects undone?

   A Atomicity B Consistency C Durability
2. 2

   In the illustrated schedule, T2 reads a value written by T1 before T1 aborts. Which anomaly has T2 experienced?

   

   A Phantom read B Dirty read C Non-repeatable read
3. 3

   A transaction reads the same row twice and obtains different committed values because another transaction updated the row between the reads. What occurred?

   A Dirty write B Phantom read C Non-repeatable read
4. 4

   The image shows the same range query returning an additional qualifying row after another transaction commits an insert. Which anomaly is illustrated?

   

   A Phantom read B Dirty read C Lost update
5. 5

   Which isolation level is intended to make concurrent transactions behave as though they executed one at a time in some serial order?

   A Read Committed B Serializable C Read Uncommitted
6. 6

   Under basic two-phase locking, what distinguishes the growing phase from the shrinking phase?

   A The growing phase changes data, while the shrinking phase only reads data B The growing phase releases shared locks, while the shrinking phase releases exclusive locks C Locks are acquired during the growing phase, and no new locks are acquired after lock release begins
7. 7

   The wait-for graph contains T1 waiting for T2, T2 waiting for T3, and T3 waiting for T1. What does this cycle indicate?

   

   A A deadlock among the three transactions B A serial execution order C A cascading commit
8. 8

   Resource R currently has a shared lock held by T1. As illustrated, T2 requests an exclusive lock on R. What should the lock manager do?

   

   A Grant the exclusive lock immediately because the transactions differ B Make T2 wait until the conflicting shared lock is released C Convert T1's shared lock into an exclusive lock
9. 9

   Both transactions in the illustrated schedule read X=100, then T1 writes X=110 and T2 writes X=120 based on its earlier read. Which anomaly occurs?

   

   A Dirty read B Phantom read C Lost update
10. 10

    A row has version V1 with balance 100 valid from timestamp 10 until 20, and V2 with balance 150 valid from timestamp 20 onward. Which balance is visible to a transaction whose MVCC snapshot timestamp is 15?

    

    A 100 from V1 B 150 from V2 C Neither version
11. 11

    What normally happens during the validation phase of optimistic concurrency control?

    A The transaction acquires exclusive locks before performing any reads B The system checks whether concurrent activity conflicts with the transaction before commit C The system permanently writes every change without checking for conflicts
12. 12

    Which rule characterizes strict two-phase locking?

    A Every lock must be released immediately after the associated operation B Shared and exclusive locks may always be granted together C Exclusive locks are held until the transaction commits or aborts
13. 13

    According to write-ahead logging, what must occur before a modified database page is written to persistent storage?

    A The corresponding log record must be made persistent B Every active transaction must commit C All database indexes must be rebuilt
14. 14

    What is the primary purpose of a savepoint inside a transaction?

    A To make all previous changes permanently durable B To establish a point to which part of the transaction can be rolled back C To release every lock held by the transaction
15. 15

    In the illustrated schedule, T2 reads a value written by T1 and commits before T1 later aborts. Which scheduling requirement is violated?

    

    A Shared-lock compatibility B Serial execution C Recoverability