MC Which of the following statements on locking is not correct? A six-lock in the MGL protocol conflicts with all other locks. correct Deadlock prevention can be achieved by implementing static 2PL. incorrect A repeatable read does not solve the phantom read problem. incorrect A 'serializable' isolation level is almost equal to 2PL. incorrect
MC Given following two statements:
i. In a rollforward recovery, the results from all recent transactions (those who are not archived yet) are completely lost.
ii. Media recovery is always based on data redundancy.
Which of these statements on recovery in transaction management is/are correct? Neither statement is correct. incorrect Both statements are correct. incorrect Statement ii is correct, but statement i is not correct. correct Statement i is correct, but statement ii is not correct. incorrect
MC Which statement is NOT CORRECT? With optimistic concurrency, locks are not used to limit simultaneity, but to detect conflicts during transaction execution, that will need to be resolved before transaction commit. incorrect An optimistic protocol assumes that conflicts between simultaneous transactions are exceptional. incorrect A serial scheduler can be considered as an extreme case of a (very) optimistic scheduler. correct A pessimistic protocol assumes it to be very likely that transactions will interfere and cause conflicts. incorrect
MC If the precedence graph contains a cycle, the schedule is... serializable incorrect not serializable correct
MC When a transaction is aborted, it is important that: A rollback of the transaction is executed: all changes made by the transaction's respective operations should be undone. correct All changes made by the individual operations belonging to that transaction should be made permanent. incorrect
MC Which of the following statements on locking is not correct? A six-lock in the MGL protocol conflicts with all other locks. correct A 'serializable' isolation level is almost equal to 2PL. incorrect Deadlock prevention can be achieved by implementing static 2PL. incorrect A repeatable read does not solve the phantom read problem. incorrect
MC Which statement is NOT CORRECT? If a transaction reads one or more data items that are being updated by another, as yet uncommitted, transaction, we may run into the uncommitted dependency problem. incorrect The inconsistent analysis problem denotes a situation where a transaction reads partial results of another transaction that simultaneously interacts with (and updates) the same data items. incorrect The lost update problem not always results in an inconsistent database state, whereas an uncommitted dependency or inconsistent analysis always yields an inconsistent database state. correct A lost update problem occurs if an, otherwise successful, update of a data item by a transaction is overwritten by another transaction that wasn't 'aware' of the first update. incorrect
MC Which of the following statements on locking is not correct? A repeatable read does not solve the phantom read problem. incorrect A 'serializable' isolation level is almost equal to 2PL. incorrect Deadlock prevention can be achieved by implementing static 2PL. incorrect A six-lock in the MGL protocol conflicts with all other locks. correct
MC Which statement is NOT CORRECT? If a transaction reads one or more data items that are being updated by another, as yet uncommitted, transaction, we may run into the uncommitted dependency problem. incorrect A lost update problem occurs if an, otherwise successful, update of a data item by a transaction is overwritten by another transaction that wasn't 'aware' of the first update. incorrect The inconsistent analysis problem denotes a situation where a transaction reads partial results of another transaction that simultaneously interacts with (and updates) the same data items. incorrect The lost update problem not always results in an inconsistent database state, whereas an uncommitted dependency or inconsistent analysis always yields an inconsistent database state. correct
MC Which concurrency problem can be described as follows: 'A transaction reads partial results of another transaction that simultaneously interacts with (and updates) the same data items.' Inconsistent analysis correct Lost update problem incorrect Uncommitted dependency incorrect Nonrepeatable read incorrect