class db {
    function openDB($db = '') {
        global $epConfig;
        if($db==''){$db=$epConfig['dbname'];}
        $_server = $epConfig['server'];
        $_dbname = $db;
        $_dbport = $epConfig['dbport'];
        $_dbuser = $epConfig['dbuser'];
        $_dbpass = $epConfig['dbpass'];
        $con = pg_connect("host=$_server port=$_dbport dbname=$_dbname user=$_dbuser password=$_dbpass");
        return $con;
    }

    function closeDB($db) {
        $cls = pg_close($db);
        $log = debug_backtrace();
        if (!$cls) {
                $this->logMessage($log);
        }
        return $cls;
    }
    function exec_query($query) {
        $q = pg_query($query);
        $log = debug_backtrace();
        if (!$q)
            $this->logMessage($log);
        return $q;
    }

$db=new db();
$connection=$db->openDB();
$db->exec_query("...sql command...");
$db->closeDB($connection);

pg_close(): supplied resource is not a valid PostgreSQL link resource