Database locking and isolation are essential concepts for managing concurrent transactions and ensuring data integrity in SQL databases. As user volume increases, applications face challenges like dirty reads, non-repeatable reads, and phantom reads, which can lead to incorrect data being displayed. To address these issues, databases adhere to ACID principles and employ various isolation levels, including READ_UNCOMMITTED, READ_COMMITTED, REPEATABLE_READ, and SERIALIZABLE, each offering different levels of data protection and concurrency control. While locks help prevent data anomalies, they can also introduce problems such as lock contention, long-term blocking, and deadlocks, which can hinder application performance. Understanding these mechanisms is crucial for developers who aim to scale applications efficiently while maintaining data consistency.