Memory issue with Dataframes.jl

dataframe.jl

using DataFrames
function inner_df(Nrow,Ncol)

    df = DataFrame(rand(Nrow,Ncol),:auto)
end

function outer_df(N)
    Nrow=76
    Ncol=21
    df=DataFrame(rand(0,Ncol),:auto)

    for i = 1:N
        append!(df,inner_df(Nrow,Ncol))
    end
    return df
end

function iterate(Niter)
    for i =1:Niter
        println(i)
        @time pan = outer_df(1000*10*10)
    end
end

iterate(10)