Advance Concepts in Storm - Real-time Analytics with Storm and Cassandra - page 221

Data aggregations over the streams
Storm's Trident framework provides two kinds of operations for performing aggregations:
• aggregate : We have covered this in an earlier section, and it works in isolated
partitions without involving network traffic
• persistentAggregate : This performs aggregate across partitions, but the
difference is that it stores the results in a source of state