When restoring from a log file, before images are compared with the current RMSfile's data records and after images are used as new values to duplicate changes. If the before image does not match the current record, the restore fails. The function making the change is recorded in the log file to identify what change is being made. Of these functions, only dupdate records both a before image and an after image. When a logical RMSfile is closed, a logical RMSfile close entry is recorded in the log file.
All transaction log records have the same basic form.
Only the begin transaction record uses the argument for the comment of the transaction. For all other types of transaction records, the argument is empty. The combination of the process ID and transaction identification uniquely identifies each transaction. The last set of log records are used when changing the format of a logical RMSfile. These records all use a format similar to the open file log record.