Oracle System Change Number (SCN): evaluate the definition and behavior.

Introduction / Context: Oracle’s System Change Number (SCN) is a cornerstone of read consistency, recovery, flashback, and replication features. Understanding that the SCN represents a monotonically increasing, database-wide logical time helps explain how Oracle ensures consistent views and coordinates recovery.

Given Data / Assumptions:

• SCN is a single logical counter for the entire database.
• It advances as the database processes changes (notably at commits and checkpoints).
• Utilities like RMAN and Data Guard rely on SCN boundaries.

Concept / Approach: Each committed transaction advances the SCN; Oracle tags blocks and undo with SCNs to reconstruct consistent snapshots for queries. During recovery, Oracle rolls forward or back to target SCNs. Thus, the description that the SCN is “database-wide and incremented whenever changes are made” captures the essential behavior (details vary internally, but this abstraction is correct).

Step-by-Step Solution:

Verification / Alternative check: Querying CURRENT_SCN before and after a COMMIT shows growth. RMAN backups record checkpoint SCNs for recoverability.

Why Other Options Are Wrong:

• SCN is not per-session and is unrelated to ROWID or block size alone.
• It applies to primary and standby databases alike.

Common Pitfalls: Assuming SCN equals physical time; confusing SCN with object identifiers.

Final Answer: Valid (SCN is a database-wide logical timestamp advanced by changes/commits)