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ACID Transactions ensure that state transformations are Atomic, Consistent, Isolated, and Durable (ACID).

Atomic operations are operations that complete entirely or not at all. So, in the earlier transfer example, both the credit and the debit would have to succeed in order for the state transformation to succeed (take effect), otherwise the state transformation fails, and the system is returned to its last well-known state.

Consistent transformations preserve the internal integrity of the resources involved. For example, deleting records from a primary table violates the referential integrity of the database if there are matching related records.

Isolated transformations appear to occur serially, one after the other, creating the illusion that no other transformations are being performed at the same time.

Durable refers to the ability to save the results of a state transformation, usually to disk, such that the results of a transformation can be recovered in the event of a system failure.
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( Topic last updated: 1999.12.01 07:58:51 PM )