In the context of computer science and databases, transactions are units of work performed within a database management system (DBMS). The states of a transaction refer to different stages or statuses that a transaction can go through during its lifecycle. The typical states of a transaction are as follows:
- Active: A transaction starts in the active state when it begins its execution. In this state, the transaction performs various operations like reading, writing, or modifying data.
- Partially Committed: After the transaction has executed all its operations successfully, it enters the partially committed state. In this state, the DBMS ensures that all the changes made by the transaction are temporarily recorded but are not yet made permanent.
- Committed: Once the transaction has been successfully executed and all its changes are permanently saved in the database, it enters the committed state. In this state, the changes become permanent and durable, and they will persist even if there are system failures.
- Aborted: If a transaction encounters an error or fails to execute successfully, it can be aborted. When a transaction is aborted, any changes made by the transaction are rolled back, and the database is restored to its previous consistent state.
- Failed: A transaction enters the failed state when it encounters a critical error or when the system fails during its execution. In this state, the transaction is unable to proceed further, and it requires manual intervention or recovery procedures to resolve the failure.
- In-Doubt: In a distributed database environment where transactions can span multiple systems or nodes, a transaction can enter the in-doubt state if there is a communication failure or network issue. In this state, the outcome of the transaction is uncertain, and it requires coordination between the different nodes to determine its final status.
These states represent the typical lifecycle of a transaction in a DBMS. The management of transactions and their states is essential to ensure data consistency, reliability, and atomicity in database operations.