A method, computer-readable medium, and device for processing a stream of records with a guarantee that each record is accounted for exactly once are disclosed. A method may receive, via a first operator, a data stream having a plurality of records, the plurality of records provided by a plurality of first data sources; allocate the data stream to a plurality of shards of the first operator; process the plurality of records by each shard of the plurality of shards to generate a first output stream, where each shard being implemented with at least two replicas; and output the first output stream to a third operator or a subscriber.