Getting Started with Your First Topology - Real-time Analytics with Storm and Cassandra - page 24

emitted to the topology to be reprocessed. For instance, in the preceding figure,
the failed tuple is emitted again.
For unreliable spouts, the tuples are not tracked using messageIds and the methods
such as ack() and fail() don't hold any value as the spout doesn't track the tuples for
successful processing. These topologies are identified as unreliable.
Note
IRichSpout is an interface provided by Storm that provides the details of the contracts or
methods to be implemented by topology spouts.