Transaction properties - ACID

ACID (atomicity, consistency, isolation, and durability) is an acronym primary attributes ensured to any transaction by a transaction manager (which is also called a transaction monitor) or simplifying is a set of properties of database transactions.

  • Atomicity. In a transaction involving two or more discrete pieces of information, either all of the pieces are committed or none are.

  • Consistency. A transaction either creates a new and valid state of data, or, if any failure occurs, returns all data to its state before the transaction was started.

  • Isolation. A transaction in process and not yet committed must remain isolated from any other transaction.

  • Durability. Committed data is saved by the system such that, even in the event of a failure and system restart, the data is available in its correct state.

The ACID concept is described in ISO/IEC 10026-1:1992 Section 4. Each of these attributes can be measured against a benchmark. In general, however, a transaction manager or monitor is designed to realize the ACID concept. In a distributed system, one way to achieve ACID is to use a two-phase commit (2PC), which ensures that all involved sites must commit to transaction completion or none do, and the transaction is rolled back.