ACID is an acronym that stands for Atomicity, Consistency, Isolation, and Durability. These properties are a set of characteristics that guarantee the reliability of database transactions. They ensure that database transactions are processed reliably even in the face of errors, system failures, or concurrent operations.
Let’s break down each ACID property:
1. Atomicity
Definition: Atomicity ensures that a transaction is treated as a single, indivisible unit of work.
Implication: Either all the changes made by the transaction are committed to the database, or none of them are. If any part of the transaction fails, the entire transaction is rolled back, and the database is left unchanged.
2. Consistency
Definition: Consistency ensures that a transaction brings the database from one valid state to another.
Implication: The database must adhere to predefined rules and constraints. If a transaction would violate these rules, it is not executed, ensuring the integrity of the data.
3. Isolation
Definition: Isolation ensures that the execution of one transaction is isolated from the execution of other transactions.
Implication: Even though multiple transactions may be executed concurrently, the outcome should be as if they were executed serially. This prevents interference between transactions and ensures data integrity.
4. Durability
Definition: Durability ensures that once a transaction is committed, its effects are permanent and survive subsequent system failures.
Implication: The changes made by a committed transaction are stored in a way that, even in the event of a power outage or system crash, they will not be lost when the system recovers.
ACID properties are fundamental to relational database systems and are crucial for ensuring data integrity and consistency in applications where the accuracy of transactions is paramount. It’s important to note that while ACID properties provide strong guarantees, there are scenarios, particularly in distributed and highly scalable systems, where relaxing some of these properties (as seen in the BASE model) may be acceptable based on specific application requirements.