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Week 8 Concurrency Control Techniques

Transaction

Problems of concurrent execution of transactions

Serialisability

Methods for serialisability

Pessimistic concurrency control

Optimistic concurrency control

Locking techniques for concurrency control

Two-phase locking

Starvation

summary Real-life example quiz



A Typical example of concurrency control in real life would be a travel company that has many branches all over the world to sell tickets for different destinations.

There is only one seat left from Paris to Nairobi on the daily flight Paris-Nairobi. Then ten passengers show up at the same time wanting to purchase ticket to Nairobi. The same airplane, the same day, the same destination.

Without concurrency control, it's possible that all passengers will end up purchasing a ticket for that one seat. However, with concurrency control, the database wouldn't allow this to happen. All passengers would still be able to access the airplane seating database, but concur-rency control would preserve data accuracy and allow only one passen-ger to purchase the seat.

1. What is not a problems due to the concurrent execution of transactions? A. The lost update problem. B. The incorrect summary or unrepeatable read problem. C. The incorrect input or unrepeatable input problem. D. The temporary update (dirty read) problem.

2. Which among the following is a method for serialisability? A. Multi-version concurrency start time. B. Multi-version concurrency control techniques. C. Stop-and-wait concurrency control techniques. D. Stock-and-wait concurrency control techniques. E. Multi-version Stop and wait concurrency control

3. The concept of locking data items is one of the main techniques used for controlling the concurrent execution of transactions. A. True B. False


Enter answer,,,. 1. 2. 3.


1. What is not a problems due to the concurrent execution of transactions? A. The lost update problem. B. The incorrect summary or unrepeatable read problem. C. The incorrect input or unrepeatable input problem. D. The temporary update (dirty read) problem.

2. Which among the following is a method for serialisability? A. Multi-version concurrency start time. B. Multi-version concurrency control techniques. C. Stop-and-wait concurrency control techniques. D. Stock-and-wait concurrency control techniques. E. Multi-version Stop and wait concurrency control

3. The concept of locking data items is one of the main techniques used for controlling the concurrent execution of transactions. A. True B. False


Enter answer,,,. 1. C 2. B 3. A


4. The problem in which each of two or more transactions is waiting for the other to release an item is called? A. Dilemma B. Deadlock C. Trilemma D. Embarrassing situation E. Lock

5. What is concurrency control? A. The management of printer in a room B. The management of users C. The management of contention for data resources. D. The management of table for data entry E. The distribution of roles for accessing data


answer is: 4. 5.


4. The problem in which each of two or more transactions is waiting for the other to release an item is called? A. Dilemma B. Deadlock C. Trilemma D. Embarrassing situation E. Lock

5. What is concurrency control? A. The management of printer in a room B. The management of users C. The management of contention for data resources. D. The management of table for data entry E. The distribution of roles for accessing data


answer is: 4. B 5. C


Education

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