An easier way of doing this would be:

my $sth = $dbh->query($query);
@ip = $sth->fetchcol(1);
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If you are looking for a faster method to retrieve your data you should take a look at the DBI documentation, particularly at the fetchrow_arrayref method and prepare/execute/bind. The Mysql module is just a wrapper on top of DBI, so you're already using it internally, but if you're going to do something a bit more involved it'll be easier to use DBI directly.