SMON Process Instance Failure

Hi,

When there is a any power outage happens and your database gets shutdown abnormally  at that time SMON process gets innitiated by the Oracle server and which works to protect instace to mantain all the components of a sga.

During startup smon will look for SCN match in datafile and controlfile if it is not found in datafile then it performs recovery from logfiles.

For committed data - Recovery can be perform from Online Redolog Files
For uncommitted data - From Undo Segment.

When the Oracle instance fails. The SMON process performs instance recovery at startup using the online redo log files.

When shutdown abort happens, oracle server gets crashed. To recover from the crash, SMON will check the online Redo data files and last SCN no in the Redo log files and SCN number in the undo tablespace are same.

If yes, it performs recovery from redo log files else it rollback the values from undo tablespace.