System change number

Question

What is an Oracle system Change number?

Satyapriya Nayak · Answer

Hi Laura The system change number (SCN) is an ever-increasing value that uniquely identifies a committed version of the database. Every time a user commits a transaction Oracle records a new SCN. You can obtain SCNs in a number of ways for example from the alert log. You can then use the SCN as an identifier for purposes of recovery. For example you can perform an incomplete recovery of a database up to SCN 1030. Oracle uses SCNs in control files datafile headers and redo records. Every redo log file has both a log sequence number and low and high SCN. The low SCN records the lowest SCN recorded in the log file while the high SCN records the highest SCN in the log file. A number internal to Oracle that is incremented over time as change vectors are generated applied and written to the Redo log . Refer http://docs.oracle.com/cd/A58617_01/server.804/a58238/ch4_impl.htm#1438 Thanks