What are the different types of concurrency control in databases?

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 conflicts.
2. Optimistic Concurrency Control: Assumes conflicts are rare and checks for conflicts before committing.
3. Timestamp Ordering: Assigns timestamps to transactions to determine the order of execution.
4. Multi-Version Concurrency Control (MVCC): Maintains multiple versions of data to allow read and write operations without locking.

Can you explain pessimistic concurrency control in more detail?

Sure! Pessimistic concurrency control involves locking resources when a transaction is being processed. This means that other transactions must wait until the lock is released before they can access the locked resources. This approach is useful in environments where conflicts are likely, as it prevents issues like dirty reads and lost updates.

What are the advantages and disadvantages of using optimistic concurrency control?

Optimistic concurrency control has several advantages, such as:

• Higher throughput: It allows more transactions to proceed without waiting for locks.
• Reduced locking overhead: Since locks are not held during the transaction, it can be more efficient.

However, it also has disadvantages:

• Conflict resolution: If conflicts do occur, transactions may need to be rolled back, which can be costly.
• Not suitable for high-conflict environments: In scenarios with frequent conflicts, it may lead to performance issues.

What is Multi-Version Concurrency Control (MVCC)?

Multi-Version Concurrency Control (MVCC) is a method that allows multiple transactions to access the database simultaneously without locking. It maintains several versions of data items, so when a transaction reads data, it can access the version that was current at the start of the transaction. This approach improves performance and reduces contention, making it ideal for read-heavy workloads.