$master_IP =
$master_dbase_user =
$master_dbase_pass =

$slave_IP =
$slave_dbase_user =
$slave_dbase_pass =

$master_dead_flag_file = '/path/to/file';


$fp = @fopen($master_dead_flag_file,"r");
$master_dead_flag = fread($fp, 1);
@fclose($fp);

if(!$fp){
	$master_dead_flag = 0;
	$fp = @fopen($master_dead_flag_file,"w+");
	@fwrite($fp,"0");
	@fclose($fp);
}



$dbase_IP   = ( !$master_dead_flag ) ? $master_IP : $slave_IP;
$dbase_user = ( !$master_dead_flag ) ? $master_dbase_user : $slave_dbase_user;
$dbase_pass = ( !$master_dead_flag ) ? $master_dbase_user : $slave_dbase_pass;

$link_id = mysql_connect($dbase_IP, $master_dbase_user, $master_dbase_user);

if (!$link_id) {
    // PUT HERE mail - master is dead
    $link_id = mysql_connect($slave_IP, $slave_dbase_user, $slave_dbase_pass);

    if (!$link_id){ ... both dead handler }

    $fp = @fopen($master_dead_flag_file,"w+");
    @fwrite($fp,"1");
    @fclose($fp);
}