Can you explain how locking mechanisms work in database transactions?

In database transactions, locks are used to manage concurrent access to data and prevent conflicts during simultaneous reading and writing. The main principle is that when a transaction reads or modifies data, it places a lock on that data so that other transactions cannot modify (or even read, depending on the lock type) until the current transaction is completed.

There are different types of locks:

• Shared lock — allows multiple transactions to read data simultaneously but prohibits writing.
• Exclusive lock — allows only one transaction to modify data, blocking access for other transactions.

Locks help ensure the properties of ACID transactions, especially isolation. However, excessive or improper use of locks can lead to deadlocks and reduce performance.

Example: if transaction A places an exclusive lock on a row for updating, transaction B, attempting to read or modify the same row, will wait until transaction A completes and releases the lock.