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SQL refers to Structured Query Language, a kind of language used to access, update and manipulate database. In SQL, ROLLBACK is a command that causes all data changes since the last START TRANSACTION or BEGIN to be discarded by the relational database management systems (RDBMS), so that the state of the data is "rolled back" to the way it was before those changes were made.
A transaction is typically started using the command BEGIN (although the SQL standard specifies START TRANSACTION). When the system processes a COMMIT statement, the transaction ends with successful completion. A ROLLBACK statement can also end the transaction, undoing any work performed since BEGIN.
The transaction, commit and rollback concepts are key to the ACID property of databases. [1] A COMMIT statement in SQL ends a transaction within a relational database management system (RDBMS) and makes all changes visible to other users. The general format is to issue a BEGIN WORK (or BEGIN TRANSACTION, depending on the database vendor ...
Once the COMMIT statement completes, the transaction's changes cannot be rolled back. COMMIT and ROLLBACK terminate the current transaction and release data locks. In the absence of a START TRANSACTION or similar statement, the semantics of SQL are implementation-dependent. The following example shows a classic transfer of funds transaction ...
A savepoint is a way of implementing subtransactions (also known as nested transactions) within a relational database management system by indicating a point within a transaction that can be "rolled back to" without affecting any work done in the transaction before the savepoint was created. Multiple savepoints can exist within a single ...
undoNextLSN: This field contains the LSN of the next log record that is to be undone for transaction that wrote the last Update Log. Commit Record notes a decision to commit a transaction. Abort Record notes a decision to abort and hence roll back a transaction. Checkpoint Record notes that a checkpoint has been made. These are used to speed up ...
Compensating transactions are also used in case where a transaction is long lived (commonly called Saga Transactions), for instance in a business process requiring user input. In such cases, data will be committed to permanent storage, but may subsequently need to be rolled back, perhaps due to the user opting to cancel the operation.
Part of the transaction log containing transactions completed by COMMIT or ROLLBACK. Because all relational databases contains, by definition, a transaction log (most of the time based on the [ARIES algorithm [Algorithms for Recovery and Isolation Exploiting Semantics]]), the log, which is a binary file, is divided into three parts, sequentially: