open F,"<squid_logfile" or die "$!";
my %counts;
#tie the file to a DB hash or something similar if memory is a concern
while(<F>){
  my $url=.... #extract url from a line of data and put it in $url
  $counts{$url}=0 if !defined $counts{$url};
  $counts{$url}++;
}
close F;
#do something with %counts to produce your report.