Memory not being freed with DBD::ODBC

I have the following script (extremley simplified)

foreach my $key (sort {$a<=>$b} keys %run){
my $inp;
$inp=$dbh->selectall_arrayref("select id, [description] from
Kaonix_import_base where idint between ? and ? ",undef,$run{$key}->[0],
$run{$key}->[1]) ;


addrec($inp); -- sub to run very heavy regexs against the select and insert
into another table
undef($inp);

}

The problem is that memory is not being freed against the statement handle
on each iteration and eventually the script stalls due lack of memories

any ideas?