MC	Which statement is NOT CORRECT?	A transaction is a set of database operations (e.g. a consecution of SQL statements in a relational database), induced by a single user or application, that should be considered as one undividable unit of work.	incorrect	Transactions typically exist in isolation, and cannot be executed concurrently with other transactions on the same data.	correct	It should not be possible to terminate a transaction in such a way that the database remains in an inconsistent state, because some operations of a single transaction were executed successfully and others were not.	incorrect	Recovery is the activity of ensuring that, whichever problem occurred, the database is returned to a consistent state afterwards, without any data loss. 	incorrect	
MC	When a transaction is aborted, it is important that:	All changes made by the individual operations belonging to that transaction should be made permanent.	incorrect	A rollback of the transaction is executed: all changes made by the transaction's respective operations should be undone.	correct	
MC	Which of the following DBMS components is involved in Transaction Management?	Scheduler	incorrect	Stored data manager	incorrect	Buffer manager	incorrect	Recovery manager	incorrect	All of these components	correct	
MC	Which statement is NOT CORRECT?	The logfile contains all updates after they have been written to disk. 	correct	The logfile contains redundant data.	incorrect	The logfile can be implemented as a sequential file.	incorrect	The logfile is often duplicated, e.g. in a RAID level 1 configuration.	incorrect	
MC	The following figure presents five transactions (T1 until T5) that are executed more or less simultaneously. Suppose a checkpoint was registered on the logfile at time tc, marking the last time when pending updates in the database buffer were persisted into the physical database files. Later, at time tf, a system fault occurred, resulting in loss of the database buffer.<br><img class="img-fluid" src="http://www.pdbmbook.com/static/quiz/fig14_5.png"><br>What recovery operations are required?	T1: nothing; T2: UNDO; T3: REDO; T4: REDO; T5: nothing	incorrect	T1: nothing; T2: REDO; T3: UNDO; T4: REDO; T5: nothing	correct	T1: REDO; T2: UNDO; T3: REDO; T4: nothing; T5: nothing	incorrect	T1: nothing; T2: REDO; T3: REDO; T4: REDO; T5: nothing	incorrect	
MC	Which statement is NOT CORRECT?	Disk mirroring is a (near) real time approach that writes the same data simultaneously to two or more physical disks	incorrect	Archiving is an approach in which database files are copied periodically to other storage media, such as tape or (another) hard disk. 	incorrect	Traditional relational databases allow for a certain measure of temporary inconsistency, in return for increased performance.	correct	There is a trade-off between the cost (overhead and storage cost) of more frequent backups and the cost of lost data because of less frequent backups.	incorrect	
MC	Which statement is NOT 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	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	
MC	If the precedence graph contains a cycle, the schedule is...	serializable	incorrect	not serializable	correct	
MC	Which statement is NOT CORRECT?	An optimistic protocol assumes that conflicts between simultaneous transactions are exceptional.	incorrect	A pessimistic protocol assumes it to be very likely that transactions will interfere and cause conflicts.	incorrect	A serial scheduler can be considered as an extreme case of a (very) optimistic scheduler.	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	
MC	Which statement is CORRECT?	Multiple transactions may hold a shared lock on the same object.	correct	Multiple transactions may hold an exclusive lock on the same object.	incorrect	
MC	Which statement is NOT CORRECT?	Deadlock prevention can be achieved by Static 2PL.	incorrect	One approach for deadlock resolution is victim selection which means choosing and aborting one of the transactions involved in the deadlock.	incorrect	The use of short-term locks violates rule 3 of the 2PL protocol, so serializability can no longer be guaranteed.	incorrect	The Read committed isolation level uses long-term read locks, but short-term write locks. 	correct	
MC	According to the MGL-Protocol, 	locks are acquired top-down, but released bottom-up in the hierarchy.	correct	locks are acquired bottom-up, but released top-down in the hierarchy.	incorrect