A rollback is a reversal of an incomplete database transaction due to problems. A transaction may fail to complete and be aborted due to:
The rollback removes any partially completed database updates from the affected user tables. The system uses the TJ (dbc.transientjournal), which contains data about incomplete transactions, including a “before image” of each modified table row, to maintain data integrity.
Also see the rollback topics in Chapter 11: “Archiving, Restoring, and Recovering Data: Operational DBAs.”