What are some techniques for concurrency control in databases?

What are some techniques for concurrency control in databases?

Concurrency control is essential for ensuring data integrity when multiple transactions occur simultaneously. Some common techniques include:

1. Locking: Prevents other transactions from accessing data until the lock is released.
2. Timestamp Ordering: Assigns a timestamp to each transaction to determine the order of execution.
3. Optimistic Concurrency Control: Assumes conflicts are rare and checks for conflicts before committing changes.
4. Multiversion Concurrency Control (MVCC): Allows multiple versions of data to exist, enabling read and write operations without blocking.

Can you explain how locking works?

Sure! Locking involves placing a lock on a data item to prevent other transactions from accessing it until the lock is released. There are different types of locks:

• Exclusive Lock: Only one transaction can hold this lock, preventing others from reading or writing the locked data.
• Shared Lock: Multiple transactions can hold this lock simultaneously, allowing them to read the data but not modify it. Locks can be applied at different levels, such as row-level or table-level, depending on the granularity needed.

What are the drawbacks of using locking?

Locking can lead to several drawbacks, including:

1. Deadlocks: Situations where two or more transactions are waiting for each other to release locks, causing a standstill.
2. Reduced Concurrency: Locking can limit the number of transactions that can be processed simultaneously, impacting performance.
3. Overhead: Managing locks adds overhead to the system, which can slow down transaction processing.

Are there alternatives to locking?

Yes, there are alternatives to locking, such as:

1. Optimistic Concurrency Control: This technique allows transactions to proceed without locking but checks for conflicts before committing.
2. Multiversion Concurrency Control (MVCC): This method maintains multiple versions of data, allowing transactions to read and write without blocking each other.
3. Snapshot Isolation: Provides a snapshot of the database at a specific point in time, allowing transactions to work with that snapshot without interference.