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 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 statement is NOT CORRECT? Recovery is the activity of ensuring that, whichever problem occurred, the database is returned to a consistent state afterwards, without any data loss. incorrect Transactions typically exist in isolation, and cannot be executed concurrently with other transactions on the same data. 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 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 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 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 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? 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 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 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? Transactions typically exist in isolation, and cannot be executed concurrently with other transactions on the same data. correct Recovery is the activity of ensuring that, whichever problem occurred, the database is returned to a consistent state afterwards, without any data loss. incorrect 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 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 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: UNDO; T3: REDO; T4: REDO; T5: nothing incorrect T1: nothing; T2: REDO; T3: REDO; T4: REDO; T5: nothing incorrect T1: nothing; T2: REDO; T3: UNDO; T4: REDO; T5: nothing correct