Transactional system

Transaction processing is designed to maintain a computer system (typically a database or some modern filesystems) in a known, consistent state, by ensuring that any operations carried out on thesystem that are interdependent are either all completed successfully or all canceled successfully.
For example, consider a typical banking transaction that involves moving $700 from a customer's savingsaccount to a customer's checking account. This transaction is a single operation in the eyes of the bank, but it involves at least two separate operations in computer terms: debiting the savingsaccount by $700, and crediting the checking account by $700. If the debit operation succeeds but the credit does not (or vice versa), the books of the bank will not balance at the end of the day. Theremust therefore be a way to ensure that either both operations succeed or both fail, so that there is never any inconsistency in the bank's database as a whole. Transaction processing is designed toprovide this.
Transaction processing allows multiple individual operations to be linked together automatically as a single, indivisible transaction. The transaction-processing system ensures that eitherall operations in a transaction are completed without error, or none of them are. If some of the operations are completed but errors occur when the others are attempted, the transaction-processingsystem "rolls back" all of the operations of the transaction (including the successful ones), thereby erasing all traces of the transaction and restoring the system to the consistent, known state that itwas in before processing of the transaction began. If all operations of a transaction are completed successfully, the transaction is committed by the system, and all changes to the database are madepermanent; the transaction cannot be rolled back once this is done.
Transaction processing guards against hardware and software errors that might leave a transaction partially completed, with the...