Data consistency means that data values are the same for all instances of an application. This data belongs together and describes a specific process at a specific time, meaning that the data is not changed during processing or transfers.
Synchronization and other protective measures help to ensure the consistency of data during multi-stage processing. Data consistency is crucial to the functioning of programs, applications, systems and databases. Locks are measures that are used to prevent data from being altered by two applications at the same time, and ensure the correct order of processing.
Data consistency can have various dimensions:
- Point in time consistency means that all related data is the same at any given instant. In the event of a power failure, for example, it is important to restore all data as it was at the moment of failure.
- Transaction consistency only exists before the specified set of transactions has been run and after they are completed. During processing, data may not be consistent.
- Application consistency may involve data from different sources such as databases and individual files. An application involves many different transactions, and as such, data is entirely consistent only before and after all transactions have been completed.
Controlling simultaneous operations and the ability to handle incomplete transactions are essential to being able to maintain as well as restore data consistency in the event of power failures.