Question

Which of the following statements is true of an optimistic approach to concurrency control?
1. During the read phase, all update operations of the transaction are
recorded in a temporary update file, which is accessed by the remaining transactions.
2. During the read phase, all update operations of the transaction are
recorded in a permanent update file, which is accessed by the remaining transactions.
3. During the write phase, the changes are temporarily applied to the
database.
4. During the write phase, the changes are permanently
applied to the database.

Answer 1

Correct Answer:

Explanation:

The optimistic approach to concurrency control assume that the conflicts are rare in the system and this is validation based protocol. This approach consider that without interfering with each other, multiple transactions can frequently complete.

This approach does not require any locking system and timestamping technique.

This approach consists of three phases:

1. Read Phase

The transaction can read any item and write operation make a local copy of the object to be modified. In other words, we can say that all updates are recorded in a temporary update file.

2. Validation Phase

In this phase, it is determined that if there is any conflict exists.

3. Write Phase

If there is no conflict and if the validation phase is successful then the transactions are recorded in the permanent update file.  

So, only option 1 and 4 are correct.