presto-main/src/main/java/io/prestosql/operator/RowNumberOperator.java/RowNumberOperator/createOperator
class RowNumberOperator:        @Override
        public Operator createOperator(DriverContext driverContext)
        {
            checkState(!closed, "Factory is already closed");

            OperatorContext operatorContext = driverContext.addOperatorContext(operatorId, planNodeId, RowNumberOperator.class.getSimpleName());
            return new RowNumberOperator(
                    operatorContext,
                    sourceTypes,
                    outputChannels,
                    partitionChannels,
                    partitionTypes,
                    maxRowsPerPartition,
                    hashChannel,
                    expectedPositions,
                    joinCompiler);
        }