Questions from Database Systems

Q: For each of the following isolation levels, give an example of

For each of the following isolation levels, give an example of a schedule that respects the specified level of isolation but is not serialize able: a. Read uncommitted b. Read committed c. Repeatable r...

Q: What benefit does strict two-phase locking provide? What disadvantages

What benefit does strict two-phase locking provide? What disadvantages result?

Q: Using the functional dependencies of Exercise 7.6, compute B

Using the functional dependencies of Exercise 7.6, compute B+.

Q: When a transaction is rolled-back under timestamp ordering, it

When a transaction is rolled-back under timestamp ordering, it is assigned a new timestamp. Why can it not simply keep its old timestamp?

Q: Show that there are schedules that are possible under the two-

Show that there are schedules that are possible under the two-phase locking protocol but not possible under the timestamp protocol, and vice versa.

Q: List four significant differences between a file-processing system and a

List four significant differences between a file-processing system and a DBMS.

Q: Consider the following SQL query on the university schema: Select

Consider the following SQL query on the university schema: Select avg (salary) - (sum(salary) / count(*)) From instructor We might expect that the result of this query is zero since the average of a s...

Q: Under a modified version of the timestamp protocol, we require that

Under a modified version of the timestamp protocol, we require that a commit bit be tested to see whether a read request must wait. Explain how the commit bit can prevent cascading abort. Why is this t...

Q: As discussed in Exercise 18.15, snapshot isolation can be

As discussed in Exercise 18.15, snapshot isolation can be implemented using a form of timestamp validation. However, unlike the multisession timestamp- ordering scheme, which guarantees serialize abil...

Q: Outline the key similarities and differences between the timestamp-based implementation

Outline the key similarities and differences between the timestamp-based implementation of the first-committer-wins version of snapshot isolation, de- scribed in Exercise 18.15, and the optimistic-concu...