Question

(ii)
d) All of these
Serializability of schedules can be ensured through a mechanism
called
a) Concurrency control
b) Evaluation control
c) Execution control
d) Cascading control
of certain relation produces Y such that Y
1​

Answer 1

Answer:

The correct answer is:

a) Concurrency control

Explanation:

Concurrency Control

In concurrency control, multiple transactions can be executed simultaneously.

This may affect the outcome of the transaction. It is extremely important to maintain the order of execution of those transactions.

There are three problems with concurrency control.

• Lost updates: When two transactions that access the same database item occur in such a way that the value of some database item becomes false, the last update problem occurs.

• Dirty read: Dirty read occurs when a transaction updates an item in the database, and then for some reason the transaction fails. The updated database item is accessed by another transaction before it is converted back to the original value.

• Unrepeatable read: Inconsistent retrievals problem is also known as unrepeatable read. When a transaction computes some summary function on a set of data while other transactions are updating the data, the inconsistent retrievals problem occurs.

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