(Excerpt from ITPUB) For Oracle, once the DML operation is submitted, first modify in the Database Buffer Cache, while saving the front image of the data in the retrace segment before modification, then modify Both the data before and the modification are written to the Redo Log Buffer. After receiving the commit command, the Redo log buffer starts writing Redo Log File and records the SCN at this time. When the redo log file is finished, it means this time. The transaction submission operation has been confirmed by the database, and only the success of the user commit completed will be given only when the Redo log file is successful. And DIRTY BUFFER in Database Buffer Cac will wait to trigger DBWN to write, but if the power is turned off, the data has been recorded in the Redo Log file, and the system will automatically roll and back when the system is restarted. Roller to ensure the consistency of data. So, as long as it is successful, the data will not be lost! And the contents of the corresponding memory in a log file (not archive mode) are not overwritten until the DBWN is written to the data file!
