Imagine a super busy restaurant where several customers are ordering at the same time. So the kitchen starts isolating the preparation process of each order to ensure that each dish is prepared correctly. This approach aligns with the isolation principle of the ACID model, which ensures that in a relational database system, transactions can execute independently without interfering with one another, even when running concurrently.
Isolation determines how the effects of one transaction are visible to other concurrent transactions. This is controlled by isolation levels following the ANSI SQL standard, which balance performance and consistency guarantees: Read Uncommitted, Read Committed, Repeatable Read, and Serializable. Each level provides increasing isolation but may introduce additional performance overhead.
PostgreSQL uses Read Committed as its default, ensuring queries only see committed data, while MySQL defaults to Repeatable Read, providing consistent reads within a transaction using MVCC (Multi-Version Concurrency Control). Both systems allow stricter levels, like Serializable for scenarios requiring maximum consistency, though at the cost of additional overhead.
These isolation levels allow developers to tailor database behavior to meet their application’s needs, balancing performance and data consistency. In summary, selecting the appropriate level of isolation depends on the use case: some applications benefit from minimal constraints for efficiency, while others demand stricter guarantees for reliability.