Transactions

A transaction is a group of changes that appear as a single change, such as the transfer of funds from a savings account to a checking account.

Transactions can be classified into the following categories:

Inquiries in which no file changes occur.
Simple transactions in which one file is changed each time you press the Enter key.
Complex transactions in which two or more files are changed each time you press the Enter key.
Complex transactions in which one or more files are changed each time you press the Enter key. These changes represent only part of a logical group of transactions.

Revisions made to files during transaction processing are journaled when using commitment control.

If the system or job ends abnormally, journaling alone can ensure that, at most, only the very last record change is lost. However, if the system or job ends abnormally during a complex transaction, the files reflect an incomplete logical transaction. For example, the job might have updated a record in file A, but before it updates a corresponding record in file B, the job ended abnormally. In this case, the logical transaction consists of two updates, but only one update had completed before the job ended abnormally.