php - MYSQLi SELECT Fetch Object

    if ( isset($_POST['update']) ){
    $db=mysqli_connect("localhost","****","****","****");
    $lasttime = isset($_POST['timestamp']) ? $_POST['timestamp'] : 0;
    while (1){
        sleep(1);
        clearstatcache();
        $mresult = mysqli_query($db,"SELECT * FROM tblchat WHERE msg_datetime > $lasttime");
        if (!empty($mresult)){ break; }
    }
    $msgs = array();
    while ($row = mysqli_fetch_object( $mresult )) { $msgs[] = $row; }
    mysqli_free_result($mresult);
    $response = array();
    $response['msgs'] = $msgs;
    echo json_encode($response);
    flush();
    mysqli_close($db);
    exit();
    }
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The code is the server for a long polling connection with client. If update is requested, the while loops check for any new messages received after the timestamp sent with the update request. If found, it puts the result in an array and echo it back to the client. The resulting output is something like this[msgs:[{msg_from:"",msg_to:"",msg:"",msg_datetime:""},{msg_from:"",msg_to:"",msg:"",msg_datetime:""}]]

The code works fine for the first time and send all the recent messages well encapsulated but then it again sends an empty array of messages. Please guide me.