Chapter 18, Problem 25E

a.

Explanation of Solution

Lock for reading a lot of tuples from relation r

• The entire logical databases may be composed of databases of multiple users which contains each user database of multiple relations and each relation of multiple tuples...

b.

Explanation of Solution

Lock for updating a lot of tuples from relation r

• If two locks IS and IX are compatible, then two IX locks and two IS locks will be compatible automatically.
• This is because it is natural to allow the both transactions T₁ and T₂ to IS lock or IX lock for reading or updating different data items...

c.

Explanation of Solution

Problems caused to the lock table while updating a large number of tuples

• When a transaction finds that a large number of tuples need to be updated actually at the run time, then owner can decide to do delayed batch processing of updates.
• Large number of updates at run time affect the similar set of nodes.
• Large number of updates is expected to have a very expensive updating cost.
• A large number of tuple updating policy performs an unnecessary number of hash functions in its predecessor path.
• The data in a database can be wrong due to a lost update that can lead to problems with normal operations.
• One method for preventing lost update is to use optimistic concurrency control to perform optimistic locking on the data...