ACID Properties

The ACID properties are a set of four guarantees that ensure the reliability and integrity of database transactions. They are the bedrock of transaction management in most relational database systems. The first property is Atomicity. This ensures that a transaction is treated as a single, indivisible 'atom' of work. Either all of the operations within the transaction are completed successfully, or none of them are. If any part of the transaction fails, the entire transaction is rolled back, and the database is left in the state it was in before the transaction began. This prevents partial updates. The second property is Consistency. This guarantees that a transaction will bring the database from one valid state to another. Any data written to the database must be valid according to all defined rules, including constraints, cascades, and triggers. The transaction cannot leave the database in an inconsistent state. The third property is Isolation. This ensures that the concurrent execution of transactions results in a system state that would be obtained if transactions were executed serially (one after another). Each transaction is 'isolated' from others, meaning that the intermediate state of one transaction is not visible to other transactions. This prevents concurrency problems like dirty reads. The final property is Durability. This guarantees that once a transaction has been successfully committed, its changes will survive permanently, even in the event of a system failure like a power outage or crash. These changes are written to non-volatile storage, such as a hard disk. Together, the ACID properties provide a powerful contract for reliable data processing.