sub cgiapp_init {
    my $self = shift;

    # ...some unrelated code...

    my $dbh = DBI->connect('dbi:mysql:database', 'user', 'password',
				 	       { RaiseError => 1 } ) or die $DBI::errstr;

    # ...more code...

    $self->param('dbh' => $dbh);
}

sub teardown {
    my $self = shift;
    $self->param('dbh')->disconnect() or die $self->param('dbh')->errstr;
}