What are the different types of locking algorithms?

What are the different types of locking algorithms?

Locking algorithms are mechanisms used in databases and concurrent programming to manage access to resources. The main types include:

1. Pessimistic Locking: Assumes conflicts will occur and locks resources before accessing them.
2. Optimistic Locking: Assumes conflicts are rare and checks for conflicts before committing changes.
3. Read/Write Locks: Allows multiple readers or a single writer, improving concurrency.
4. Two-Phase Locking (2PL): Ensures serializability by acquiring locks in two phases: growing and shrinking.

Can you explain pessimistic locking in more detail?

Sure! Pessimistic locking involves locking a resource as soon as it is accessed, preventing other transactions from modifying it until the lock is released. This approach is useful in environments with high contention, as it avoids conflicts by ensuring that only one transaction can access the resource at a time.

What are the advantages and disadvantages of using optimistic locking?

Optimistic locking allows multiple transactions to proceed without locking resources initially, which can improve performance in low-contention scenarios. However, if a conflict occurs, the transaction may need to be rolled back, which can lead to wasted resources and increased complexity in handling retries.

How does two-phase locking ensure serializability?

Two-phase locking ensures serializability by requiring that all locks be acquired in the first phase (growing phase) and released in the second phase (shrinking phase). This prevents cycles in the wait-for graph, ensuring that transactions can be serialized without conflicts.