Question

To ensure exactly-once processing in a data pipeline during a system failure, which specific property must the data ingestion pattern possess?

Accepted Answer

To ensure exactly-once processing during a system failure, the data ingestion pattern must possess the property of idempotency. An operation is idempotent if performing it multiple times produces the same result as performing it once. In a data pipeline, failures often cause the system to retry processing a piece of data that was already partially or fully processed. Without idempotency, these retries would result in duplicate records or incorrect calculations. Achieving this requires the system to use a unique identifier for each piece of data, often called a correlation ID or primary key. When the system processes data, it checks this identifier against a persistent state store to see if the data has already been handled. If the identifier exists, the system discards the redundant data or ignores the request, ensuring the outcome remains the same regardless of how many times the ingestion process is triggered. By combining this with atomic transactions, where the update to the state store and the data processing are committed as a single unit, the system prevents partial updates during failures and guarantees that each data point is reflected in the final output exactly once.

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To ensure exactly-once processing in a data pipeline during a system failure, which specific property must the data ingestion pattern possess?