In Oracle Database, what does the System Change Number (SCN) represent with respect to database activity?

Introduction / Context:
The System Change Number (SCN) is a cornerstone of Oracle’s consistency and recovery architecture. Understanding SCN helps explain read consistency, Flashback queries, and media recovery.

Given Data / Assumptions:

• Oracle uses SCNs to label points in time within the database.
• SCNs advance as changes are committed and recorded.

Concept / Approach:
SCN is a monotonically increasing logical timestamp. The database increments SCN as changes occur, enabling consistent snapshots and recovery to specific points in time.

Step-by-Step Solution:

Verification / Alternative check:
Oracle documentation ties SCN advancement to commit processing and redo generation, enabling features like Flashback Query AS OF SCN.

Why Other Options Are Wrong:
Dirty reads are prevented by Oracle’s consistency model; SCN is not incremented by them.
Deadlocks and explicit locks are concurrency control events, not the basis for SCN increments.

Common Pitfalls:
Confusing SCN with wall-clock time; SCN is logical, not tied to actual timestamps, though they can be mapped.

Final Answer:
A value that is incremented whenever database changes are made.