1. A method, comprising steps of: executing a query execution plan, said query execution plan including a first aggregation operator and a second aggregation operator that is a record source for said first aggregation operator, wherein said first aggregation operator and said second aggregation operator perform a same aggregation operation; wherein executing the second aggregation operator comprises: generating an initial version of a batch of aggregation records based on a first set of records from an input source; determining that one or more second records from the input source may not be aggregated with any existing aggregation record of said batch of aggregation records, and in response, sending the one or more second records to said first aggregation operator without updating said batch of aggregation records; and sending the batch of aggregation records to the first aggregation operator; wherein executing the first aggregation operator comprises aggregating aggregation records and second records received from the second aggregation operator; wherein the method is performed by one or more computing devices.