What is ACID?

ACID is an acronym that stands for Atomicity, Consistency, Isolation, and Durability. It is a set of properties that guarantee reliable processing of database transactions. These properties are essential for ensuring data integrity and reliability in database systems. Here's a brief explanation of each property.

Atomicity

This property ensures that a transaction is treated as a single, indivisible unit of work. Either all the changes made in a transaction are applied, or none of them are. If any part of a transaction fails, the entire transaction is rolled back and the database remains unchanged. In Rails, database transactions are used to ensure atomicity. For example, consider a banking application where you want to transfer money between two accounts. You can use a transaction to ensure that both the debit and credit operations are atomic

ActiveRecord::Base.transaction do
  sender_account.debit(amount)
  receiver_account.credit(amount)
end

If an exception occurs during either the debit or credit operation, the entire transaction is rolled back, ensuring atomicity.

Consistency

Consistency ensures that a transaction moves the database from one consistent state to another. You can use Rails validations and database constraints to enforce data consistency. For example, you can add validations to your models to ensure that certain fields meet certain criteria, and you can set up foreign key constraints in the database to maintain referential integrity.

# make sure you will also add validation on db migration level too.
class User < ApplicationRecord
  validates :email, presence: true, uniqueness: true
end

Isolation

Isolation ensures that concurrent transactions do not interfere with each other. It prevents one transaction from accessing data that another transaction is modifying until the first transaction is complete. This feature helps maintain data integrity in multi-user environments. Rails uses database transactions to manage isolation. When multiple requests or threads are modifying the same data simultaneously, Rails uses database-level locks and isolation levels to ensure that one transaction's changes do not interfere with another's until they are committed.

Durability

Durability guarantees that once a transaction is committed, its effects are permanent and will survive any subsequent system failures, such as crashes or power outages. This means that the changes made by a committed transaction are safely stored and will not be lost.

Summary

In summary, ACID features are critical to maintaining data integrity and reliability in database systems, and Rails provides tools and mechanisms for implementing these features in your applications.