Which statement defines idempotence?

• A. An operation is idempotent if repeated requests produce different results.
• B. An operation is idempotent if it is performed only once and never repeated.
• C. An operation is idempotent if repeated requests produce the same effect as a single request.
• D. An operation is idempotent if it changes state each time it is called.

Answer: (C)

Idempotence means that repeating the same operation yields the same effect as doing it once. The important point is that after the first application, subsequent identical requests don’t cause additional changes to the state. The initial call may alter something, but repeats don’t accumulate further effects.

Think of it like this: if you fetch data, you should get the same result every time; if you update a resource to a given state, sending that same update again should leave the resource in that same state; if you delete something, it should remain gone on subsequent deletes. This is what makes an operation safe to repeat without changing the end result.

The other ideas—if repeated requests produced different results, or if the operation must only run once and never again, or if it changes state with every call—don’t fit the concept of idempotence.