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.

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