Although I really like Discipulus's approach to parallel processing the file, I thought I'd throw out Tie::File as an option. I've used it a couple of times successfully years ago. It doesn't load the entire file at once; instead, it reads it in chunks and presents the file as an array.

Instead of doing:

while (<$fh>){
    ...
}
[download]

You'd do something like the following after opening the file with the distribution:

for (@fh){
    ...
}
[download]