MC	If the precedence graph contains a cycle, the schedule is...	not serializable	correct	serializable	incorrect	
MC	Which statement is NOT CORRECT?	If the precedence graph contains a cycle, the schedule is serializable.	correct	The logfile contains redundant data.	incorrect	Multiple transactions may hold a shared lock on the same object.	incorrect	The logfile can be implemented as a sequential file.	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: REDO; T2: UNDO; T3: REDO; T4: nothing; T5: nothing	incorrect	T1: nothing; T2: REDO; T3: REDO; T4: REDO; T5: nothing	incorrect	T1: nothing; T2: UNDO; T3: REDO; T4: REDO; T5: nothing	incorrect	T1: nothing; T2: REDO; T3: UNDO; T4: REDO; T5: nothing	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 statement is NOT CORRECT?	The logfile is often duplicated, e.g. in a RAID level 1 configuration.	incorrect	The logfile can be implemented as a sequential file.	incorrect	The logfile contains redundant data.	incorrect	The logfile contains all updates after they have been written to disk. 	correct	
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	
MC	Which statement is CORRECT?	Recovery is the activity of ensuring that, whichever problem occurred, the database is returned to a consistent state afterwards, without any data loss. 	correct	A serial scheduler can be considered as an extreme case of a (very) optimistic scheduler.	incorrect	Multiple transactions may hold an exclusive lock on the same object.	incorrect	The logfile contains all updates after they have been written to disk. 	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	If the precedence graph contains a cycle, the schedule is...	serializable	incorrect	not serializable	correct