sub prepare_cached {
	my ($dbh, $statement, $attr, $allow_active) = @_;
	# Needs support at dbh level to clear cache before complaining about
	# active children. The XS template code does this. Drivers not using
	# the template must handle clearing the cache themselves.
	my $cache = $dbh->FETCH('CachedKids');
	$dbh->STORE('CachedKids', $cache = {}) unless $cache;
	my @attr_keys = ($attr) ? sort keys %$attr : ();
	my $key = ($attr) ? join("~~", $statement, @attr_keys, @{$attr}{@attr_keys}) : $statement;
	my $sth = $cache->{$key};
	if ($sth) {
	    if ($sth->FETCH('Active') && ($allow_active||0) != 2) {
		Carp::carp("prepare_cached($statement) statement handle $sth was still active")
		    if !$allow_active;
		$sth->finish;
	    }
	    return $sth;
	}
	$sth = $dbh->prepare($statement, $attr);
	$cache->{$key} = $sth if $sth;
	return $sth;
    }