What are the different types of concurrency control?

What are the different types of concurrency control in databases?

Concurrency control is a database management technique to ensure that multiple transactions can occur simultaneously without conflicting. 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.

Can you explain pessimistic concurrency control in more detail?

Sure! Pessimistic concurrency control assumes that conflicts will occur, so it locks the data being accessed. This means that when a transaction wants to read or write data, it must first acquire a lock. Other transactions must wait until the lock is released. This method is useful in environments with high contention for resources, but it can lead to decreased performance due to waiting.

What are the advantages and disadvantages of optimistic concurrency control?

Optimistic concurrency control has several advantages:

• Higher throughput: Transactions can proceed without waiting for locks, improving performance in low-contention scenarios.
• Reduced locking overhead: It avoids the overhead of managing locks.

However, it also has disadvantages:

• Conflict resolution: If conflicts occur, transactions may need to be rolled back, which can be costly.
• Not suitable for high contention: In environments with many conflicting transactions, it can lead to increased rollbacks and decreased performance.

How does timestamp-based concurrency control work?

Timestamp-based concurrency control assigns a unique timestamp to each transaction. When a transaction wants to read or write data, it checks the timestamps of other transactions that have accessed the same data. If a conflict is detected (e.g., a later transaction tries to read data modified by an earlier one), the system can either roll back the later transaction or prevent it from proceeding. This method helps maintain a consistent order of operations based on the timestamps.