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- Oracle.1Z0-898.v2018-04-11.q63
- Question 55
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Question 55/63
A named query that sets an exclusive pessimistic on the entities returned by the query by setting the NamedQuery lockMode element to LockModeType.PESSIMISTIC_FORCE_INCREMENT. The application starts transaction and executes the query.
Which of the following statements is correct about the entities returned by the query?
Which of the following statements is correct about the entities returned by the query?
Correct Answer: A
Explanation/Reference:
The lock modes LockModeType.PESSIMISTIC_READ, LockModeType.PESSIMISTIC_WRITE, and LockModeType.PESSIMISTIC_FORCE_INCREMENT are used to immediately obtain long-term database locks.
The semantics of requesting locks of type LockModeType.PESSIMISTIC_READ, LockModeType.PESSIMISTIC_WRITE, and LockModeType.PESSIMISTIC_FORCE_INCREMENT are the following.
If transaction T1 calls for a lock of type LockModeType.PESSIMISTIC_READ or LockModeType.PESSIMISTIC_WRITE on an object, the entity manager must ensure that neither of the following phenomena can occur:
P1 (Dirty read): Transaction T1 modifies a row. Another transaction T2 then reads that row and obtains the modified value, before T1 has committed or rolled back.
P2 (Non-repeatable read): Transaction T1 reads a row. Another transaction T2 then modifies or deletes that row, before T1 has committed or rolled back.
PESSIMISTIC_FORCE_INCREMENT
Pessimistic write lock, with version update.
Reference: javax.persistence, Enum LockModeType
The lock modes LockModeType.PESSIMISTIC_READ, LockModeType.PESSIMISTIC_WRITE, and LockModeType.PESSIMISTIC_FORCE_INCREMENT are used to immediately obtain long-term database locks.
The semantics of requesting locks of type LockModeType.PESSIMISTIC_READ, LockModeType.PESSIMISTIC_WRITE, and LockModeType.PESSIMISTIC_FORCE_INCREMENT are the following.
If transaction T1 calls for a lock of type LockModeType.PESSIMISTIC_READ or LockModeType.PESSIMISTIC_WRITE on an object, the entity manager must ensure that neither of the following phenomena can occur:
P1 (Dirty read): Transaction T1 modifies a row. Another transaction T2 then reads that row and obtains the modified value, before T1 has committed or rolled back.
P2 (Non-repeatable read): Transaction T1 reads a row. Another transaction T2 then modifies or deletes that row, before T1 has committed or rolled back.
PESSIMISTIC_FORCE_INCREMENT
Pessimistic write lock, with version update.
Reference: javax.persistence, Enum LockModeType
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