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What is transaction recovery?
Transaction Recovery is an application recovery whereby the effects of specific transactions during a specified timeframe are removed from the database. Historically, recovery was performed primarily to overcome disasters and hardware failures. Any number of problems can occur at the application level.
What is rollback recovery?
The roll back recovery algorithm is based on a pattern similar to the two-phase commit protocol. When a failure occurs in a process, the process recovers or rolls back to a previously consistent state and sends a request to all other processes to restart.
What is rollback transaction used for?
Rolls back an explicit or implicit transaction to the beginning of the transaction, or to a savepoint inside the transaction. You can use ROLLBACK TRANSACTION to erase all data modifications made from the start of the transaction or to a savepoint. It also frees resources held by the transaction.
How does a ROLLBACK recovery scheme work?
Rollback-recovery from a consistent set of checkpoints appears deceptively simple. The following scheme seems to work: Whenever a process rolls back to its checkpoint, it notifies all other processes to also roll back to their respec- tive checkpoints. It then installs its checkpointed state and resumes execution.
Can you rollback a transaction after COMMIT?
You cannot roll back a transaction once it has commited. You will need to restore the data from backups, or use point-in-time recovery, which must have been set up before the accident happened.
Can rollback transaction can perform undo operation?
Use the ROLLBACK statement to undo work done in the current transaction or to manually undo the work done by an in-doubt distributed transaction. Note: Oracle recommends that you explicitly end transactions in application programs using either a COMMIT or ROLLBACK statement.
What is the effect of a rollback transaction?
ROLLBACK TRANSACTION statements in triggers terminate the batch containing the statement that fired the trigger; subsequent statements in the batch are not executed. The effect of a ROLLBACK on cursors is defined by these three rules: With CURSOR_CLOSE_ON_COMMIT set ON, ROLLBACK closes, but does not deallocate all open cursors.
Is there a way to recover with concurrent transactions?
During recovery, it would be very difficult for the recovery system to backtrack all the logs and then start recovering. Recovery with concurrent transactions can be done in the following four ways. In this scheme, the recovery scheme depends greatly on the concurrency control scheme that is used.
Can a transaction be rolled back after a commit is executed?
A transaction cannot be rolled back after a COMMIT TRANSACTION statement is executed, except when the COMMIT TRANSACTION is associated with a nested transaction that is contained within the transaction being rolled back. In this instance, the nested transaction is rolled back, even if you have issued a COMMIT TRANSACTION for it.
How does a ROLLBACK statement in a stored procedure work?
ROLLBACK TRANSACTION statements in stored procedures do not affect subsequent statements in the batch that called the procedure; subsequent statements in the batch are executed. ROLLBACK TRANSACTION statements in triggers terminate the batch containing the statement that fired the trigger; subsequent statements in the batch are not executed.