Transaction log contents: are after-change copies called “before images”?

Introduction / Context:Recovery systems use logs to reconstruct database state. Log records may include “before images” (state prior to change) and “after images” (state after change). This question checks whether you can distinguish the terminology.

Given Data / Assumptions:

• Before image: the original value(s) prior to an operation; used for UNDO.
• After image: the resulting value(s) after the operation; used for REDO.
• Different DBMSs implement logical, physiological, or physical logging, but the naming is consistent.

Concept / Approach:The statement calls after-change copies “before images,” which reverses the meaning. In logging strategies (e.g., ARIES), both before and after images can be present depending on the operation and logging mode.

Step-by-Step Solution:Identify the claim: post-change copies are labeled “before images.”Recall definition: “before” is pre-change; “after” is post-change.Therefore, the statement is incorrect.

Verification / Alternative check:Review REDO/UNDO logic: before image enables rollback; after image enables roll-forward after a crash.

Why Other Options Are Wrong:Logging style (physical vs. logical) does not swap the names; page-level vs. row-level scope is unrelated to terminology.

Common Pitfalls:Assuming every log always stores both images; some systems optimize and log only what is needed for recovery guarantees.

Final Answer:Invalid statement