What are the existing methods of idempotency?

Idempotence means that performing the same operation multiple times with the same input data results in the same system state as performing it once.

Methods to ensure idempotence include:

• Applying unique identifiers (Idempotency Key): The client sends a unique key with each request. The server stores information about requests made with this key and returns the result of the first successful execution for subsequent requests with the same key, without processing the request again.

• Precondition checks: Before executing an operation, the system's state is checked. If the system is already in the desired state, the operation is not performed.

  • Example: When trying to create a record, it checks whether a record with the same key parameters already exists.

• Using versioning/ETags: When updating a resource, the client includes the current version or ETag of the resource. The server performs the update only if the version/ETag on the server matches the one sent by the client, preventing the re-update of outdated data.

• Transactional operations: Grouping multiple actions into a single transaction. If the transaction is interrupted or repeated, the system should revert to the original state or complete the transaction atomically.

• Using asynchronous queues with "exactly-once" delivery guarantee: Some queue systems (e.g., Kafka with certain settings) can guarantee message delivery exactly once, helping to avoid duplication during processing.

• Checking execution results: After a potentially non-idempotent operation, it is checked whether the desired state has been reached. If necessary, corrective actions are taken only if the state does not meet the requirements.