batchaggregator plugin invoking aggregate method twice

[Vikram Singh]

Hi Guys, I am working on one aggegrator plugin and trying to overwrite the method - 

This method is being invoked twice with same data, could you please suggest what I am missing? 

@Override
public void aggregate(String groupKey, Iterator<StructuredRecord> iterator,
                      Emitter<StructuredRecord> emitter) throws Exception {

  }