ACID

Term added on Saturday 15th June, 2024 by Team

ACID, an acronym that stands for Atomicity, Consistency, Isolation, and Durability, is a set of properties that ensure the reliability and integrity of database transactions. In simple terms, ACID guarantees that database transactions are processed reliably, ensuring that data remains consistent and accurate, even in the face of errors, system failures, or concurrent access.

A database transaction is a sequence of operations performed as a single logical unit of work. It may involve reading, creating, updating, or deleting data in one or more database tables. ACID properties ensure that these transactions are processed correctly and completely, or not at all, maintaining the integrity and consistency of the database.

Let’s explore each of the ACID properties in more detail:

Atomicity: Atomicity ensures that a transaction is treated as an indivisible unit of work, meaning that either all of its operations are completed successfully, or none of them are executed. If any part of the transaction fails, the entire transaction is rolled back, leaving the database in its original state, as if the transaction never happened.
Consistency: Consistency ensures that a transaction moves the database from one valid state to another valid state. It guarantees that all data integrity constraints and rules are enforced, ensuring the accuracy and correctness of the data within the database.
Isolation: Isolation ensures that concurrent transactions do not interfere with each other. It guarantees that each transaction operates in its own isolated environment, unaffected by other concurrent transactions. This property prevents issues such as dirty reads, non-repeatable reads, and phantom reads, which can occur when multiple transactions access and modify the same data concurrently.
Durability: Durability ensures that once a transaction is committed, its effects are permanent and survive system failures, power outages, or other unexpected events. This property guarantees that any changes made by a successful transaction are safely stored in the database and can be recovered in the event of a system failure.

Here’s an example that illustrates the importance of ACID properties in a banking scenario:

Imagine a banking application where a customer wants to transfer $1,000 from their savings account to their checking account. This operation involves two separate transactions: deducting $1,000 from the savings account and adding $1,000 to the checking account.

Without ACID properties, various issues could arise:

If the transaction is not atomic, the first operation (deducting $1,000 from savings) might succeed, but the second operation (adding $1,000 to checking) could fail, resulting in lost funds.
If the transaction is not consistent, it might violate data integrity rules, such as allowing a negative balance in the savings account.
If the transaction is not isolated, concurrent transactions from other customers could interfere with the transfer, leading to inaccurate balances or data corruption.
If the transaction is not durable, a system failure or power outage during the transfer could result in the loss of data, leaving the accounts in an inconsistent state.

By adhering to the ACID properties, the banking application ensures that the transfer operation is treated as a single, indivisible unit of work (atomicity). It maintains data integrity by ensuring that account balances remain consistent (consistency). It isolates the transfer operation from other concurrent transactions (isolation), and it guarantees that the changes made by the successful transaction are permanently stored in the database (durability).

ACID properties are fundamental to ensuring the reliability and integrity of database transactions, making them essential in applications that require data accuracy and consistency, such as banking, e-commerce, healthcare, and financial systems. By implementing ACID-compliant database systems, organizations can maintain data integrity, prevent corruption, and provide reliable and trustworthy services to their users.

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