databaserollback

Databaserollback refers to the process by which a database reverts to a previous consistent state by undoing the effects of one or more uncommitted transactions. It is a core mechanism for preserving atomicity in the ACID properties of many relational and some non-relational databases. Rollback is typically triggered explicitly by a ROLLBACK statement or implicitly when a transaction fails due to constraint violations, deadlocks, or system errors.

Implementation relies on logging: write-ahead logs or undo logs record a transaction's changes before they are applied to the data files. If a rollback is issued, the system uses these logs to reverse the changes. Some systems also maintain redo logs to support recovery after a crash. The exact behavior can vary by database engine, but the goal is to restore the data to its state at the start of the transaction or at a defined savepoint.

The scope of a rollback is usually limited to the currently active transaction. Savepoints allow partial rollback within a transaction, and some databases support nesting or compensating actions for rolled-back work. In distributed environments, rollback can be coordinated with two-phase commit or compensated transactions to maintain consistency across multiple nodes.

Crash recovery combines undo and redo to bring the database to a consistent state, applying committed changes and discarding incomplete ones. Best practices include keeping transactions short, using explicit savepoints, and ensuring sufficient logging and backup to support correct rollback and recovery.