Apache Storm Component Guide
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Processing Reliability

Storm provides two types of guarantees when processing tuples for a Storm topology.

Table 4.3. Processing Guarantees



At least once

Reliable; Tuples are processed at least once, but may be processed more than once. Use when subsecond latency is required and for unordered idempotent operations.

Exactly once

Reliable; Tuples are processed only once. (This feature requires the use of a Trident spout and the Trident API. For more information, see Trident Concepts.)