ACID (Atomicity, Consistency, Isolation, and Durability)
Tags: beginners, database, learning, tutorial
Published: 2024-03-02 12:52:46

A brief, under 1k words article about ACID. Good start if you don't know what it is.

## Intro

In the realm of software development, managing data with precision and reliability is more than a necessity—it's the bedrock upon which systems that power our digital world stand. At the heart of these systems are databases, tasked with handling an ever-growing volume of data, from financial transactions to social media posts. Ensuring the integrity, availability, and consistency of this data, especially in the face of errors or system failures, is paramount. This is where the concept of ACID comes into play—a set of principles designed to guarantee that database transactions are processed reliably.

The acronym ACID stands for **Atomicity**, **Consistency**, **Isolation**, and **Durability**.

## Short background Story

The ACID principles, foundational to database management since the 1980s, were formalized by [Andreas Reuter](https://en.wikipedia.org/wiki/Andreas_Reuter) and [Theo Härder](https://en.wikipedia.org/wiki/Theo_H%C3%A4rder) to address the need for reliable transaction processing.

These principles were coined to address the complexities of transaction management in database systems, ensuring data integrity and error handling in a myriad of scenarios. The concept has evolved alongside the database technologies, from the [hierarchical](https://en.wikipedia.org/wiki/Hierarchical_database_model#:~:text=A%20hierarchical%20database%20model%20is,field%20containing%20only%20one%20value) and [network](https://en.wikipedia.org/wiki/Network_model#:~:text=In%20computing%2C%20the%20network%20model,being%20a%20hierarchy%20or%20lattice.) models of the early days to the sophisticated relational and NoSQL databases that underpin modern applications.

## The ACID Properties

**Atomicity** - it guarantees that a series of operations within a database transaction are treated as a single unit, which either all succeed or fail together. Imagine an online banking transfer, atomicity ensures that transferring money from one account to another either completes entirely or does not happen at all, preventing scenarios where money is deducted from one account without being credited to another. **Databases achieve atomicity through techniques like transaction logs, which record changes to be made during a transaction**. If a failure occurs, the system can revert to the original state by "rolling back" these changes.

**Consistency** - it ensures that a transaction transforms the database from one valid state to another, adhering to all predefined rules, such as data types, constraints, and cascading updates. For instance, if a bank’s database has a rule that the balance cannot be negative, a withdrawal transaction that would result in a negative balance is not permitted. **Database management systems enforce consistency by validating transactions against the schema and constraints before committing them**.

**Isolation** - it deals with the visibility of transactions to each other. To maintain data accuracy, it's crucial that concurrent transactions do not interfere with each other. **Isolation is managed through concurrency control mechanisms, ensuring that transactions operate as if they were executed in sequence**, even if they run concurrently. For example, if two people attempt to purchase the last ticket for a concert at the same time, isolation ensures that only one purchase goes through, avoiding double booking.

**Durability** - it assures that once a transaction is committed, it remains so, even in the event of a power loss, crash, or error. This property ensures that the effects of the transaction are permanently recorded in the database. **Techniques such as [write-ahead logging](https://en.wikipedia.org/wiki/Write-ahead_logging) help achieve durability by ensuring that transaction logs are saved to permanent storage before the actual transaction data is updated**.

## So why is ACID important?

ACID compliance is crucial for databases that support critical operations, where data integrity and reliability cannot be compromised. **These principles provide a framework for database management systems to handle data in a predictable and safe manner, ensuring that transactions are processed correctly even under adverse conditions.**

In distributed databases or systems where transactions span multiple databases, achieving ACID compliance becomes more challenging but equally vital.

Modern solutions often involve sophisticated algorithms and distributed consensus protocols to maintain ACID properties across a network of databases.

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Hope you liked this short introduction to ACID. Cheers!

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