Based on your question, I'd propose a different method:

Method 3:

Parse the data as it's available: You can use File::Tail to open the file and read the data (even while another program is generating the file). This allows you to continuously read / parse / write. Thus, you can begin processing your data before you have the full terabyte.

For example, suppose we use the following to generate a stream of data:

#!/usr/bin/perl 
#    stream_write.pl - Slowly generate data
use strict; 
use warnings; 
 
open my $OFH, '>', 'the_stream.dat' or die $!; 
binmode( $OFH, ":unix"); 
my $cnt = 0; 
while ($cnt < 100) { 
    ++$cnt; 
    my $cur_time = time; 
    print $OFH "$cnt, $cur_time\n"; 
    sleep 5*rand; 
}   
close $OFH;
[download]

Then we can use something like this to read and parse the data while the original is running:

#!/usr/bin/perl
#   stream_read.pl - Read, parse & print data as it's available
use strict;
use warnings;

use File::Tail;
my $IFH = File::Tail->new(
    name=>"the_stream.dat",
    tail=>-1,  # Start at the beginning
);
while (defined(my $line = $IFH->read)) {
    chomp $line;
    my $cur_time = time;
    my ($old_time, $cnt) = split /,\s*/, $line;
    print "$cur_time  data: $old_time, $cnt\n";
}
[download]

Then, when I ran them, the output of stream_read.pl was:

$ perl stream_read.pl
1310035999  data: 1, 1310035990
1310035999  data: 2, 1310035992
1310035999  data: 3, 1310035992
1310035999  data: 4, 1310035994
1310035999  data: 5, 1310035994
1310035999  data: 6, 1310035998
1310035999  data: 7, 1310035999
1310035999  data: 8, 1310035999
1310035999  data: 9, 1310035999
1310036001  data: 10, 1310036000
1310036001  data: 11, 1310036000
1310036008  data: 12, 1310036004
1310036014  data: 13, 1310036008
1310036014  data: 14, 1310036010
.....
[download]

...roboticus

When your only tool is a hammer, all problems look like your thumb.

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