applicationconsistent

Applicationconsistent, often described as an application-consistent state, refers to a backup or replication capture in which the target application's data is in a transactionally consistent condition at the moment of the backup. This typically requires ensuring that in-flight transactions are completed or paused, in-memory changes are flushed to durable storage, and the application is briefly quiesced to prevent partial writes from being saved.

This level of consistency sits between crash-consistent and file-system-consistent backups. Crash-consistent backups reflect the state as if a crash occurred, without guarantees about application data structures, while file-system-consistent backups guarantee filesystem integrity without ensuring application-level correctness.

In practice, achieving applicationconsistency often involves coordinated mechanisms such as volume shadow copy service (VSS) writers on Windows or equivalent quiescing interfaces on other platforms. Backup software coordinates with the application to flush caches, pause new I/O, take the snapshot, and resume operations. Applications that commonly provide dedicated writers include SQL Server, Exchange, Oracle, and various enterprise systems, though not all software supports automatic application consistency.

The primary benefit is reliable restores that preserve transactional integrity and reduce post-restore reconciliation. Limitations include the need for application support, potential performance impact during quiescing, and cases where complex or custom workloads cannot be fully application-consistent. In such instances, backups may be classified as file-system- or crash-consistent and require additional validation during recovery.

See also: backup types, disaster recovery, data integrity, point-in-time recovery, snapshots.