ACID

Atomicity, Consistency, Isolation, and Durability

A set of properties that guarantee the reliability and correctness of transactions in a database management system (DBMS), particularly in relational database management systems (RDBMS). The ACID properties ensure that the database remains in a consistent state even in the case of system failures, crashes, or errors. Here’s a brief explanation of each ACID property:

1. Atomicity: Atomicity ensures that a transaction is either fully completed or not executed at all. In other words, if any part of the transaction fails, the entire transaction is rolled back to its initial state, and no changes are made to the database. This ensures that the database is never left in an inconsistent or partially updated state.
2. Consistency: Consistency ensures that the database transitions from one consistent state to another after a transaction is completed. This means that the database starts in a consistent state, and once a transaction is executed successfully, it ends in another consistent state. Consistency is achieved by enforcing data integrity constraints, such as primary keys, foreign keys, and other validation rules.
3. Isolation: Isolation ensures that concurrent transactions are executed independently of each other, and their intermediate results are not visible to other transactions. This means that the changes made by one transaction are not visible to other transactions until the transaction has been completed. Isolation helps prevent conflicts and inconsistencies that can arise when multiple users access and modify the database simultaneously.
4. Durability: Durability guarantees that once a transaction has been successfully completed, its changes to the database are permanent and will not be lost in case of a system failure, crash, or restart. This is typically achieved by writing transaction logs to non-volatile storage, which can be used to recover the database to its most recent consistent state after a failure.

The ACID properties play a critical role in maintaining the integrity, consistency, and reliability of a database, making them an essential aspect of database management systems.

• Abbreviation: ACID