ACID

ACID is a set of properties of database transactions intended to guarantee data integrity despite errors, power failures, and other mishaps. The acronym ACID stands for Atomicity, Consistency, Isolation, and Durability. These properties ensure that database transactions are processed reliably and guarantee the correctness and reliability of the data in the database.

Atomicity

Atomicity guarantees that each transaction is treated as a single "unit", which either succeeds completely or fails completely. If any part of a transaction fails, the entire transaction fails and the database state is left unchanged. This property ensures that the database remains in a consistent state and prevents partial updates to the database that could cause data corruption.

Consistency

Consistency ensures that a transaction can only bring the database from one valid state to another, maintaining the integrity of the database. Database consistency is achieved by adhering to all defined rules, including constraints, cascades, and triggers. If a transaction results in a violation of any of these rules, the entire transaction is rolled back and the database remains unchanged.

Isolation

Isolation ensures that concurrent execution of transactions leaves the database in the same state that would have been obtained if the transactions were executed serially. This property prevents transactions from interfering with each other. Isolation is typically achieved through concurrency control mechanisms such as locking and timestamping.

Durability

Durability guarantees that once a transaction has been committed, it will remain so, even in the event of power loss, crashes, or errors. This property ensures that the database keeps track of pending changes in such a way that the server can recover from an abnormal termination.

Implementation

Implementing ACID properties requires careful design and coordination among the database system's components. Techniques such as logging and checkpointing are commonly used to ensure durability, while locking and multiversion concurrency control can be used to achieve isolation.

Challenges

While the ACID properties offer strong guarantees for transaction processing, they can also lead to performance bottlenecks in high-volume or distributed systems. In such environments, alternative models such as BASE (Basically Available, Soft state, Eventual consistency) are sometimes preferred for their ability to offer improved scalability and performance at the cost of weaker consistency guarantees.

See also

• Database management system
• Transaction processing
• Concurrency control
• Distributed database
• BASE (database model)