In a database system, a transaction is a unit of work that is executed on the database. A transaction may involve one or more database operations, such as reading or writing data, and is typically performed by a user or application program. During its execution, a transaction can be in different states that reflect its progress and status. The most common states of transactions are:
Active state:In the active state, a transaction has started but has not yet completed its execution. The transaction is executing its operations and making changes to the database. At this stage, the transaction may acquire locks on the data items it accesses to prevent conflicts with other transactions.
Partially committed state:In the partially committed state, a transaction has completed its execution and is ready to commit its changes to the database. However, the changes have not been made permanent yet. In this state, the transaction has sent a commit request to the database, but the database has not yet acknowledged the request. If a failure occurs at this stage, the transaction will need to be rolled back to undo its changes.
Committed state:In the committed state, a transaction has completed its execution successfully and its changes have been made permanent in the database. The transaction has received an acknowledgement that its changes have been committed, and the database has released the locks it acquired during its execution. Once a transaction has reached the committed state, its changes are visible to other transactions and can be used as part of their operations.
Aborted state:In the aborted state, a transaction has failed during its execution and its changes are rolled back or undone. This can happen when a transaction encounters an error, is canceled by the user, or is rolled back as a result of a deadlock or other conflict with other transactions. In this state, the transaction releases all the locks it acquired during its execution, and the database is restored to the state it was in before the transaction started.
Overall, these states of transactions are essential for ensuring the consistency and correctness of the data in the database, and for providing a reliable and predictable mechanism for managing concurrent access to the database.
