MC Which statement is CORRECT? In a shared memory architecture, multiple interconnected processors that run the DBMS software share the same central storage and secondary storage. incorrect With a shared disk architecture, each processor has its own central storage but shares secondary storage with the other processors. incorrect In a shared nothing architecture, each processor has its own central storage and hard disk units. incorrect All statements are CORRECT. correct MC With horizontal fragmentation... each fragment consists of a subset of the columns of the global data set. incorrect each fragment consists of rows that satisfy a certain query predicate. correct MC Which statement is NOT CORRECT? Location transparency means that database users do not need to know on which node the required data resides. incorrect Fragmentation transparency refers to the fact that users can execute global queries, without being concerned with the fact that distributed fragments will be involved, and need to be combined, to perform the query. incorrect Transaction transparency refers to the fact that the distributed database can be accessed and queried in a uniform fashion, regardless of the different database systems and APIs that may be involved. correct Replication transparency means that different replicas of the same data item will be automatically kept consistent by the database system and updates to one replica will be propagated transparently (be it synchronously or asynchronously) to the other copies of the same data item. incorrect MC Which statement is NOT CORRECT? Primary site 2PL comes down to applying the centralized Two-Phase Locking protocol in a distributed environment. incorrect A disadvantage of Primary site 2PL is that the central lock manager may become a bottleneck. incorrect With distributed 2PL, every site has its own lock manager, which is responsible for managing all locking data pertaining to the fragments stored on that site. incorrect Even if the database contains replicated data, applying the basic 2PL protocol still suffices to guarantee serializability. correct MC A schedule in 2PL is deadlock free if... both the local and global wait-for graphs contain no cycles. correct the local wait-for graphs contain no cycles. incorrect the global wait-for graph contains only a limited number of cycles. incorrect the local wait-for graph contains only a limited number of cycles. incorrect MC Optimistic concurrency may considerably increase transaction throughput and overall data availability in a... tightly coupled setting. incorrect loosely coupled setting. correct MC Many NoSQL databases apply some form of... vertical fragmentation. incorrect horizontal fragmentation. correct MC Eventual consistency in a NoSQL environment implies that... the results of a database transaction will eventually be propagated to all replicas and if no further transactions are executed then the system will eventually become consistent. correct the results of a database transaction will immediately be propagated to all replicas. incorrect the database is consistent at all times. incorrect the database is inconsistent at all times. incorrect MC With BASE transactions, conflict resolution... always happens at the moment of writing the data. incorrect may be postponed until the data is actually read. correct MC Quorum based protocols essentially enforce consistency between replicas of the same data item by means of three configurable parameters N (the number of nodes to which a data item is replicated), R (the minimum number of nodes that should respond before a read operation for a data item can be considered as completed) and W (the minimum number of nodes that should receive the updated value before a write operation for a data item can be considered as completed), with R <= N and W <= N.

Which statement is NOT CORRECT? A higher N also allows for more parallelism, but at the same time increases the overhead if one needs to keep all N replicas permanently consistent. incorrect A higher R increases the chance that the set of replicas that is returned by these R nodes contains an up to date version of the data item. incorrect The higher W is, the faster the write performance, since the response time is determined by the fastest of these W nodes. correct By manipulating R and W, the database administrator can decide on the trade-off between performance and consistency, but also on the trade-off between read performance and write performance. incorrect