PHP 连接oracle

function connect_oracle(){

    static $dbconn = false;
    if(!$dbconn){
        $db_server = "127.0.0.1";
        $db_user = "zzzz";
        $db_pass = "zzzzzz123";
        $db_sid = "MBDWV2";
        $dbconn = OCILogon($db_user,$db_pass,"(DESCRIPTION =
                  (ADDRESS_LIST =
                      (ADDRESS = (PROTOCOL = TCP)(HOST = {$db_server})(PORT = 1521))
                    )
                    (CONNECT_DATA =
                      (SERVICE_NAME = {$db_sid})
                    )
                  )","utf8");
        if($dbconn==false)
           die("无法连接oracle");
    }
    return $dbconn;
}