Describe the principle of idempotency in RESTful APIs and why it matters for data synchronization.

• A. An idempotent operation must be executed only once and cannot be retried.
• B. Idempotent operations fail if run more than once.
• C. An idempotent operation can be executed multiple times with the same effect; ensures safe retries in data sync and prevents duplicate changes.
• D. An idempotent operation means every call changes data differently.

Answer: (C)

Idempotency means that making the same request multiple times has the same effect as making it once. In RESTful APIs, this lets a caller retry a request after a transient failure without stacking changes or creating duplicates. This is crucial for data synchronization between systems because network hiccups or timeouts often necessitate retries. When an operation is idempotent, repeated attempts converge to the same final state, so you won’t end up with multiple updates or inconsistent data.

Think of an update that sets a resource to a specific value via a safe, idempotent method. If that request is sent again, the resource remains in the same state as after the first successful call. That safe retry behavior is exactly what data synchronization needs: you can retry without risking duplicate changes or drift between systems.

The best description captures that idea: an idempotent operation can be executed multiple times with the same effect, enabling safe retries in data synchronization and preventing duplicate changes. The other statements describe conditions that don’t align with idempotency—for example, demanding that retries never occur, or claiming each retry changes data differently—so they don’t fit the concept.