use List::MoreUtils qw/natatime/;

    sub select_in_chunks {
	my ($self, $set_1, $set_2) = @_;
	
	my @ret;
	my $chunk_size = 450;
	my $it1 = natatime $chunk_size, @$set_1;

	while (my @a = $it1->()) {
		my $it2 = natatime $chunk_size, @$set_2;
		
		while (my @b = $it2->()) { 
                        # previous query with subsets
			my $records = $self->query(\@a, \@b)
			
			push @ret, @$records;
		}
	}

        return \@ret;
    }