December 2010 - Question No 18

18. Which of the following is an optimistic concurrency control method ?

(A) Validation based
(B) Time stamp ordering
(C) Lock-based
(D) None of these

Explanation:-

In order to know the answer for this let us first go through what concurrency control means. When many people try to make modifications to a database at any point of time, there should be a system of controls in place to ensure that changes made by one do not adversely affect the other. This is called concurrency control. THere are basically two major categories of concurrency control and types under them.
Types of concurrency control

1. Pessimistic methods
   1. Timestamp ordering methods
   2. Serialization graph testing
   3. Locking methods
2. Optimistic methods
   1. Backward validation methods
   2. Forward validation methods
   3. Hybrid methods

The main idea behind pessimistic method is that it is assumed that transaction could be problem prone. In optimistic method it is assumed that transaction may not face any problem. Optimistic methods are deadlock-free whereas pessimistic method is deadlock-prone. We can look at it in detail depending on any question which we will come across in future. In june 2011 paper -II we had the following question.
The basic variants of time-stamp- based method of concurrency control are
(A) Total time stamp-ordering
(B) Partial time stamp ordering
(C) Multiversion Time stamp ordering
(D) All of the above
We will look at all such questions later.

Ans:-A