In terms of implementation where does Storm stores the derived aggregation into? Does it use any embedded key value store etc?

[#1 · Accepted solution]

@milind pandit

Storm core has abstractions for bolts to save and retrieve the state of its operations. There is a default in-memory based state implementation and also a Redis backed implementation that provides state persistence.

Currently the only kind of State implementation that is supported is KeyValueState which provides key-value mapping.

Bolts that requires its state to be managed and persisted by the framework should implement the IStatefulBolt interface or extend the BaseStatefulBolt and implement void initState(T state) method.

Please see following link for details:

http://storm.apache.org/releases/2.0.0-SNAPSHOT/State-checkpointing.html