@Override
public void merge(FunctionContext ctx, Tuple part) {
AvgContext avgCtx = (AvgContext) ctx;
ProtobufDatum datum = (ProtobufDatum) part.get(0);
AvgLongProto proto = (AvgLongProto) datum.get();
avgCtx.sum += proto.getSum();
avgCtx.count += proto.getCount();
}