My recommendation for data in this size if you want to do your own sorting is to use DB_File's BTree method. Right now tilly's scratchpad has the following snippet:

use strict;
use DB_File;

my %sorted;
$DB_BTREE->{compare} = sub {$_[1] cmp $_[0]};
tie (%sorted, 'DB_File', undef, O_RDWR|O_CREAT, 0640, $DB_BTREE) or di
+e $!;

%sorted = 1..30;
print map "$_\n", keys %sorted;
[download]

which shows how to create an in memory BTREE with an arbitrary sort order. If you follow tye's suggestion you can skip the arbitrary BTREE, use a temporary file rather than in memory, make the keys be your sort key, and the values be your data. Just insert into the hash and then loop over it using the each construct. (Not keys because that will cause a slurp.)

If your OS has large file support, your limit is available disk space. If it does not have large file support, your limit is about 2 GB for the temp file, which is a data structure for (considering the BTREE overhead) somewhat over a GB of data. (I would guestimate about 1.3 GB.)

There is also a File::Sort out there. I prefer the arbitrary text of DB_File rather than having the assumption of lines imposed on me. And if you want to sort data structures rather than text, be sure to look at MLDBM (and expect a big slowdown).