From Oracle FAQ
SCN can refer to:
- System Change Number - A number, internal to Oracle that is incremented over time as change vectors are generated, applied, and written to the Redo log.
- System Commit Number - A number, internal to Oracle that is incremented with each database COMMIT.
The SCN is an ever-increasing value that uniquely identifies a committed version of the database at a point in time. Every time a user commits a transaction Oracle records a new SCN in redo logs. 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.
Note: System Commit Numbers and System Change Numbers share the same internal sequence generator.
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