如何记录查询执行时间

我试图实现慢查询日志到我的数据库类，但我得到奇怪的结果。它目前正在记录"大多数"所有查询，它说大多数查询需要大约0.8秒才能运行，我不明白，因为这是在我的开发机器上，而不是在繁重的负载下。

地狱，我甚至尝试在phpMyAdmin中运行查询，他们非常快。

我放错地方了吗?还是我错过了什么?

class database {
    protected $_mysqli;
    protected $_debug;
    public function __construct($host, $username, $password, $database, $debug) {
        $this->_mysqli = new mysqli($host, $username, $password, $database);
        $this->_debug = (bool) $debug;
        if (mysqli_connect_errno()) {
            if ($this->_debug) {
                echo mysqli_connect_error();
                debug_print_backtrace();
            }
            return false;
        }
        return true;
    }
    public function q($query) {
        $incomingq = $query;
        if ($query = $this->_mysqli->prepare($query)) {
            if (func_num_args() > 1) {
                $x = func_get_args();
                $args = array_merge(array(func_get_arg(1)),
                    array_slice($x, 2));
                $args_ref = array();
                foreach($args as $k => &$arg) {
                    $args_ref[$k] = &$arg;
                }
                call_user_func_array(array($query, 'bind_param'), $args_ref);
            }
            // Settings
            $SLOW_LOG_TIME = 0.8; // (sec)
            $SLOW_LOG_FILE = 'php_slow.txt';
            $SLOW_LOG_START = time(); // (sec)
            $query->execute();
            // Logging
            $SLOW_LOG_END = microtime(TRUE);
             $time = $SLOW_LOG_END - $SLOW_LOG_START;
            if ($time > $SLOW_LOG_TIME)
            {
                $log = date('Y-m-d H:i:s') . "'t" . round($time, 3) . "'t" . $_SERVER['SERVER_NAME'] . $_SERVER['REQUEST_URI'] . "'t" . str_replace(array("'t" , "'n"), "", $incomingq) . "'r'n";
                $fp = fopen($SLOW_LOG_FILE, 'a+');
                fwrite($fp, $log);
                fclose($fp);
            }
            if ($query->errno) {
                if ($this->_debug) {
                    echo mysqli_error($this->_mysqli);
                    debug_print_backtrace();
                }
                return false;
            }
            if ($query->affected_rows > -1) {
            // if ($query->sqlstate == "00000") {
                return $query->affected_rows;
            }
            $params = array();
            $meta = $query->result_metadata();
            while ($field = $meta->fetch_field()) {
                $params[] = &$row[$field->name];
            }
            call_user_func_array(array($query, 'bind_result'), $params);
            $result = array();
            while ($query->fetch()) {
                $r = array();
                foreach ($row as $key => $val) {
                    $r[$key] = $val;
                }
                $result[] = $r;
            }
            $query->close();
            return $result;
        }
        else {
            if ($this->_debug) {
                echo $this->_mysqli->error;
                debug_print_backtrace();
            }
            return false;
        }
    }
    public function handle() {
        return $this->_mysqli;
    }
    public function last_insert_id()
    {
        return $this->_mysqli->insert_id;
    }
}