Chapter 18: Problem 9

Discuss two multiversion techniques for concurrency control.

Short Answer

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The two multiversion techniques for concurrency control discussed here are the Timestamp Ordering Protocol and Multiversion Read Consistency. The former manages conflicts by assigning unique timestamps to transactions and prioritizing older ones. The latter technique increases system throughput by allowing transactions to access the version of the data present when the transaction began, reducing delays caused by simultaneous transactions.

Step by step solution

Understanding of Concurrency Control

Concurrency control is a method used in database management systems (DBMS) to address conflicts that emerge when several transactions are attempting to access the same data simultaneously. This technique is essential for maintaining the integrity and consistency of data in a database environment, especially in systems where multiple users have access to the same data.

Introduction of Multiversion Techniques

Multiversion Concurrency Control (MVCC) is a popular method of concurrency control in databases. It allows multiple transactions to access the same data without conflicting with each other by producing different versions ('copies') of the same data. Transactions then work with these copies, which prevents them from interfering with each other.

Explanation of Timestamp Ordering Protocol

One of the techniques of multiversion concurrency control is the Timestamp Ordering Protocol. This method assigns a unique timestamp to each transaction, identifying which sequence they belong in. Transactions with older timestamps are given priority over newer ones. If a newer transaction attempts to access data currently being used by an older transaction, it's made to wait until the older transaction is completed. Similarly, if an older transaction attempts to access data that has been accessed by a newer transaction, it gets cancelled and restarted.

Explanation of Multiversion Read Consistency

Multiversion Read Consistency is another technique which ensures consistency by creating versions of data items for each transaction. With this technique, a transaction doesn't have to wait for other transactions to finish; it can proceed by reading the version of the data that was present when the transaction began. This method helps increase system throughput by reducing the number of conflicts and delays caused by simultaneous transactions, but it can come at the cost of increased memory usage due to multiple versions of data items being stored.

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Discuss two multiversion techniques for concurrency control.

Short Answer

Step by step solution

Understanding of Concurrency Control

Introduction of Multiversion Techniques

Explanation of Timestamp Ordering Protocol

Explanation of Multiversion Read Consistency

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