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Oracle must re-do all redo-log transactions that have both a BEGIN and a COMMIT entry (roll forward), and it must undo all transactions that have a BEGIN entry but no COMMIT entry (roll back). [6] (Re-doing a transaction in this context simply means applying the information in the redo log files to the database; the system does not re-run the ...
Issuing the commands ROLLBACK or COMMIT will also discard any savepoints created since the start of the main transaction. Savepoints are defined in the SQL standard and are supported by all established SQL relational databases, including PostgreSQL , Oracle Database , Microsoft SQL Server , MySQL , IBM Db2 , SQLite (since 3.6.8), Firebird , H2 ...
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. If autocommit was disabled with the start of a transaction, autocommit will also be re-enabled with the end of the transaction.
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.
For systems without a commit/rollback mechanism available, one can undo a failed transaction with a compensating transaction, which will bring the system back to its initial state. Typically, this is only a workaround which has to be implemented manually and cannot guarantee that the system always ends in a consistent state.
A commit is an act of committing. The record of commits is called the commit log. In terms of transactions, the opposite of commit is to discard the tentative changes of a transaction, a rollback. The transaction, commit and rollback concepts are key to the ACID property of databases. [1]
Presumed abort or Presumed commit are common such optimizations. [2] [3] [5] An assumption about the outcome of transactions, either commit, or abort, can save both messages and logging operations by the participants during the 2PC protocol's execution. For example, when presumed abort, if during system recovery from failure no logged evidence ...
On the other hand, rotation can be used "to select the place in the redo list where the next undo operation will put the command". [1] The list of redo is therefore unordered. "To undo an isolated command, the user has to undo a number of steps, rotate the redo list, and then redo a number of steps". [1]