# find prev. pattern intersection
                        my $intersection_length = 0;
                        while (my $pmh = shift @prev_msg_hashes) {
                           if ($pmh eq $messages[$intersection_length]->{hash}) { $intersection_length ++ }
                           else { $intersection_length = 0 }
                        }

                        my @new_msgs = @messages[$intersection_length .. $#messages];