Question

Write a short note on optimistic scheduling

Answer 1

Optimistic concurrency control

Optimistic concurrency control (OCC) is a concurrency control method applied to transactional systems such as relational database management systems and software transactional memory. OCC assumes that multiple transactions can frequently complete without interfering with each other. While running, transactions use data resources without acquiring locks on those resources. Before committing, each transaction verifies that no other transaction has modified the data it has read. If the check reveals conflicting modifications, the committing transaction rolls back and can be restarted.[1]Optimistic concurrency control was first proposed by H.T. Kung and John T. Robinson.[2]

OCC is generally used in environments with low data contention. When conflicts are rare, transactions can complete without the expense of managing locks and without having transactions wait for other transactions' locks to clear, leading to higher throughput than other concurrency control methods. However, if contention for data resources is frequent, the cost of repeatedly restarting transactions hurts performance significantly; it is commonly thought[who?] that other concurrency control methods have better performance under these conditions.[citation needed] However, locking-based ("pessimistic") methods also can deliver poor performance because locking can drastically limit effective concurrency even when deadlocks are avoided.

Answer 2

Answer: The optimistic method of concurrency control is based on the hypothesis that conflicts of database operations are rare and that it is better to let transactions run to completion and only check for conflicts before they are committed.

Explanation:

To Find : Write a short note on optimistic scheduling

Concept :

The optimistic method of concurrency control is based on the hypothesis that conflicts of database operations are rare and that it is better to let transactions run to completion and only check for conflicts before they are committed. An optimistic concurrency control method in database operations are also known as validation or certification methods. No checking for conflict is done while the transaction is executing. The optimistic method of concurrency control does not require locking or timestamping techniques. Whereas, a transaction is executed without restrictions until it is committed. In optimistic methods, each transaction moves through the following phases during execution:

• Read phase.
• Validation or certification phase.
• Write phase.

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