for(my $i = 1; $i < 50; $i++) {    
    my $start = "aaa";
    my %hash; keys %hash = 250_000;    ### pre-allocate the hash

    for(my $j = 1; $j < 250000; $j++)    {
        my $val = "$cnt $i $j $start";
        $hash{$val} = $cnt;            ### Simple hash assignments
        
        $cnt++;
        $start++;
    }
    $h_item_selector[$i] = \%hash;     ### then assign a reference
}