Well, either dws is right on the money (which is my guess too), or somehow you are really stuck in this ugly situation where you have a big, unsorted Apache log file. Say, perhaps, you are tossed a big concatenated log file from a cluster of 5 machines. guh..

After kicking the sysadmin who gave you such an ugly problem, I would first split the file down into smaller chunks (files, in this case) that your machine can handle. Here's a way to quickly split the file into separate files by month.

# untested.  copy/paste errors from working code are possible.  :)
use FileHandle;
my %files = ();

while (<INPUT>) { # you can open the file by yourself  :)
  # Get date of log line
  my $date;
  if (m|^[^\[]+\[\d+/(\w+)/(\d+)|) {
     $date = ("$1\_$2.log");  
  }
  else { next; } # reject bad log line

  if (! defined $files{$date}) {
    $files{$date} = new FileHandle;
    open $files{$date}, ">$date" or die "Couldn't open $date: $!\n";
  }
  print { $files{$date} } $_;
}
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