Which statement best describes idempotence in API/db operations?

• A. An operation can only be applied once
• B. An operation must be atomic
• C. An operation can be applied multiple times with same result as first
• D. An operation has no effect on failure

Answer: (C)

Idempotence means an operation can be performed multiple times and the end state of the system is the same as if it were performed once. In API or database contexts, this matters for reliability when retries occur: you want repeated identical requests to not cause additional changes after the first one.

For example, sending a PUT request to set a resource to a specific value should produce that value whether the request is made once or several times in a row. A DELETE that removes a resource is also idempotent if subsequent delete requests don’t induce more changes beyond having the resource already gone. Because of this, repeated executions yield the same result rather than accumulating effects.

That’s why the correct description is that an operation can be applied multiple times with the same result as the first. The other ideas mix in different properties: one-time execution is not the defining trait, atomicity is about all-or-nothing transactions, and failure behavior isn’t what defines idempotence.