PreImage Transaction Processing (also called PREIMG or "pre-image") provides high-speed and guaranteed atomic transactions without transaction logging. PreImage Transaction Processing enjoys many of the benefits of transaction control, including full commit and rollback, with a relatively small increase in processing overhead.
Unlike Full Transaction Processing, file updates are not logged to the server’s transaction logs. For this reason, PreImage files are not recoverable in the event of an abnormal server termination. In such a situation, a PreImage file is in an unknown state because an unknown number of updates may have not yet been written to disk at the time of the abnormal server termination.
Because automatic recovery does not process PreImage files, a PreImage file rebuilt after an abnormal server termination is not guaranteed to be in a consistent transaction state. In such a situation, PreImage files could contain data that was in the process of being committed but for which the commit had not yet been completed.
Because no protection from catastrophic failure is provided, it is important to provide other means for data recovery when using this mode.