Which lock should be obtained to prevent a concurrent transaction from executing a conflicting read, insert or delete operation on the same key value.
A. Higher-level lock
B. Lower-level lock
C. Read only lock
D. Read write
Answer:A
Which lock should be obtained to prevent a concurrent transaction from executing a conflicting read, insert or delete operation on the same key value.
A. Higher-level lock B. Lower-level lock C. Read only lock D. Read write
Explanation: Operations acquire lower-level locks while they execute, but release them when they complete; the corresponding transaction must however retain a higher-level lock in a two-phase manner to prevent concurrent transactions from executing conflicting actions. 2. Once the lower-level lock is released, the operation cannot be undone by using the old values of updated data items, and must instead be undone by executing a compensating operation; such an operation is called