DBMS Korth Edition 4 Exercise 15 Question 12 (Page No. 590)

Question

What is a cascadeless schedule ? Why is cascadelessness of schedules desirable ? Are there any circumstances under which it would be desirable to allow noncascadeless schedules ? Explain your answer.

Answer 1

Let’s say there are 2 transactions in the system (T1 and T2).

Cascadeless schedule:

In Cascadeless Schedule, if a transaction is going to perform read operation on a value, it has to wait until the transaction who is performing write on that value commits.

Say if T1 is performing write operation. Now If T2 wants to read, then it has to wait until T1 commits.

Why it is desirable?

Because the failure of a transaction does not lead to the aborting of any other transaction

When Non – Cascadeless schedule are desirable?

• Cascadeless schedule may result in less concurrency. So if the failure occurs very rarely then we can choose “increased concurrency” by using Non – Cascadeless schedule