What are the types of concurrency control?

What are the different types of concurrency control in databases?

Concurrency control is essential in databases to ensure data integrity when multiple transactions occur simultaneously. The main types include:

1. Pessimistic Concurrency Control: Locks resources to prevent other transactions from accessing them until the lock is released.
2. Optimistic Concurrency Control: Allows transactions to proceed without locking resources, but checks for conflicts before committing.
3. Timestamp-based Concurrency Control: Assigns a timestamp to each transaction and uses it to determine the order of operations.
4. Multi-Version Concurrency Control (MVCC): Maintains multiple versions of data to allow transactions to read without waiting for locks.

Can you explain how optimistic concurrency control works?

Sure! Optimistic concurrency control assumes that conflicts are rare. It allows transactions to execute without locking resources. Before a transaction commits, it checks if any other transaction has modified the data it read. If a conflict is detected, the transaction is rolled back; otherwise, it commits successfully.

What are the advantages of using MVCC?

MVCC offers several advantages:

1. Increased Concurrency: Multiple transactions can read data simultaneously without waiting for locks.
2. Reduced Lock Contention: Since readers don’t block writers and vice versa, it minimizes delays.
3. Improved Performance: It enhances performance in read-heavy environments, as transactions can proceed without interference.

Are there any downsides to using pessimistic concurrency control?

Yes, there are some downsides to pessimistic concurrency control:

1. Reduced Performance: Locking can lead to delays, especially in high-traffic environments.
2. Deadlocks: If two transactions hold locks and wait for each other to release them, it can cause a deadlock situation.
3. Resource Overhead: Managing locks requires additional resources and can complicate transaction management.