What is meant by transaction rollback? What is meant by cascading rollback?
Answers
Answer:
Transaction rollback means that, if a transaction has failed after a disk write, the writes need to be undone.
Means that,
To maintain atomicity, a transaction’s operations are redone or undone.
Undo : Restore all BFIM s on to disk (Remove all AFIM s)
Redo: Restore all AFIM s on to disk.
Data base recovery is achieved either by performing only Undo s or only Redo s by a combination of the two.
These operations are recorded in the log as they happen.
If in a schedule, failure of one transaction causes several other dependent transactions to rollback or abort, then such a schedule is called as a Cascading Schedule or Cascading Rollback or Cascading Abort.
It simply leads to the wastage of CPU time.
Answer:
A rollback is the operation of restoring a database to a previous state by canceling a specific transaction or transaction set. Rollbacks are either performed automatically by database systems or manually by users.
A cascading rollback occurs in database systems when a transaction (T1) causes a failure and a rollback must be performed. Other transactions dependent on T1's actions must also be rollbacked due to T1's failure, thus causing a cascading effect. That is, one transaction's failure causes many to fail.