An activity or request. Orders, purchases, changes, additions and deletions are typical business transactions stored in the computer. Transactions update one or more master files and serve as both an audit trail and history for future analyses. Ad hoc queries are a type of transaction as well, but are usually just acted upon and not saved. Transaction volume is a major factor in figuring computer system size and speed.
Keeping Transactions in Sync
A major problem in a transaction processing system is ensuring that all master files are updated before the transaction is considered completely processed. For example, if two files must be updated, but a system failure occurs after the first one, but before the second one, the software must be able to roll back the first update and start over later. In a distributed environment, this is called "two-phase commit." See transaction file