Idempotency

Idempotency refers to the property of certain operations, particularly in computing and web services, where performing the same operation multiple times produces the same result as performing it once. This concept is crucial in ensuring that repeated requests or operations do not cause unintended side effects or changes, making systems more reliable and predictable.

Also known as: Repeatability, Safe operation, Deterministic operation, Consistent operation.

Comparisons

• Idempotency vs. Idempotent Method: Idempotency is the property itself, while an idempotent method is a specific operation (like an HTTP PUT or DELETE request) that exhibits this property, meaning it can be repeated without changing the result.
• Idempotency vs. Retries: While retries involve repeating an operation to handle failures, idempotency ensures that the result remains consistent and unchanged regardless of how many times the operation is retried.

Pros

• Reliability: Ensures that repeated operations do not produce unexpected outcomes, which is essential for fault-tolerant systems.
• Predictability: Makes systems more predictable, as repeated actions yield the same result, simplifying error handling.
• Ease of Implementation: Reduces the need for complex checks to prevent duplicate operations, as idempotent operations inherently handle them.

Cons

• Implementation Complexity: Designing operations to be idempotent can add complexity, especially in systems where actions typically produce side effects.
• Overhead: Ensuring idempotency might require additional logic or checks, potentially introducing performance overhead.
• Limited Use Cases: Not all operations can or should be idempotent, particularly those that naturally involve side effects, like financial transactions.

Example 

In an API, an HTTP PUT request to update a user’s profile is idempotent because sending the same request multiple times will not change the result beyond the first application. The user’s profile will be updated to the same state, regardless of how many times the update request is made.