Whenever power outage occurs or instance crashes, during nex startup of the database, SMON performs instance recovery.
Instance Recovery is nothing but roll forward as well as roll backward. In order to perform instance recovery, SMON scans undo as well as redo(online redo log files).
Roll backward means, removing uncommited data from the respective data files.
Roll forward means, writing commited data to the respective data file which was not written earlier.
SMON also coeleses the adjacent free space in the data files.
Once the sorting operations are completed, SMON drops the temporary segmemts.
