Questions from Database Systems

Q: Consider a relation r (A, B, C) and

Consider a relation r (A, B, C) and a transaction T that does the following: find maximum A value. Assume that an index is used to find the maximum a value. a. Suppose that the transaction locks each tu...

Q: Explain the phantom phenomenon. Why may this phenomenon lead to an

Explain the phantom phenomenon. Why may this phenomenon lead to an incorrect concurrent execution despite the use of the two-phase locking proto- col?

Q: Explain the reason for the use of degree-two consistency.

Explain the reason for the use of degree-two consistency. What disadvantages does this approach have?

Q: Show that the following decomposition of the schema R of Exercise 7

Show that the following decomposition of the schema R of Exercise 7.1 is not a lossless decomposition:

Q: Give example schedules to show that with key-value locking,

Give example schedules to show that with key-value locking, if lookup, insert, or delete does not lock the next-key value, the phantom phenomenon could go undetected.

Q: Many transactions update a common item (e.g., the

Many transactions update a common item (e.g., the cash balance at a branch) and private items (e.g., individual account balances). Explain how you can in- crease concurrency (and throughput) by orderi...

Q: Most implementations of database systems use strict two-phase locking.

Most implementations of database systems use strict two-phase locking. Suggest three reasons for the popularity of this protocol.

Q: Consider the following locking protocol: All items are numbered, and

Consider the following locking protocol: All items are numbered, and once an item is unlocked, only higher-numbered items may be locked. Locks may be released at any time. Only X-locks are used. Show...

Q: Using the university schema, write an SQL query to find the

Using the university schema, write an SQL query to find the ID and name of each instructor who has never given an A grade in any course she or he has taught. (Instructors who have never taught a course...

Q: Consider a variant of the tree protocol called the forest protocol.

Consider a variant of the tree protocol called the forest protocol. The database is organized as a forest of rooted trees. Each transaction Ti must follow the following rules: • The first lock in each...