Processing Reliability
Storm provides two types of guarantees when processing tuples for a Storm topology.
Table 1.3. Processing Guarantees
| Guarantee | Description | 
|---|---|
| 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. Requires the use of a Trident spout and the Trident API. | 

