Database Basics Series: Understanding SQL Isolation Levels

We are starting a new series on Databases, covering Basic, Intermediate, and Advanced concepts. This is the first article in the Database Basics Series!

ACID

Relational database systems that support transactions offer ACID guarantees for transactions. So, what do we mean when we say that a database is ACID compliant -

• Atomicity: Guarantees that each transaction is treated as a single unit, either completed entirely or not. This property ensures that any changes made during the transaction are rolled back in case of failure, leaving the database state unchanged.
• Consistency: Ensures that a transaction can only bring the database from one valid state to another, maintaining database invariants. This means that any transaction will leave the database in a consistent state according to the defined rules and constraints.
• Isolation: Defines how transaction modifications affect data visibility to other transactions. The level of isolation determines the balance between concurrency and data consistency.
• Durability: Once a transaction has been committed, it guarantees that the changes made are permanent, even in the case of a system failure. This is often achieved through logging and recovery mechanisms.

This article will focus on Isolation in ACID compliance and how databases support different Isolation Levels to balance the trade-offs between consistency…