Notification system with php and socket.io

I am trying to create a notification system with php and socket.io. The idea is that clients connect to socket.io and wait for notification. The PHP script connects to socket.io via curl on a different port and even publishes an update that is sent to the connected clients. Clients are identified through the ID that they send in the message after the connection event. I keep the socket variable associated with user_id. Everything works fine, but after a while the script stops working. It looks like after a while the socket variable is stored in an array. However my server-side code is posted below

var notification_port = 8001;
var oak_port          = 8002;

var io = require('socket.io').listen(notification_port);
var clients = new Array();

io.sockets.on("connection", function(socket){
   socket.on("__identification", function(message){
      if (message.id){
         console.log("user with session id " + message.id + " connected!");
         var sockets = clients[message.id];
         if (!sockets){
            sockets = new Array();
         }
         sockets.push(socket);
         clients[message.id] = sockets;
      }
   });
});

var url  = require('url');
var oakListener = require('http').createServer(function (req, res) {
  res.writeHead(200, {'Content-Type': 'text/plain'});

  var url_parts = url.parse(req.url, true);
  var query = url_parts.query;

  var sockets = clients[query.id];
  if (sockets){
     for (var i = 0; i < sockets.length; i++){
        sockets[i].emit("notification", query);
      }
      res.end('ok');
  } else {
     res.end('failed');
  }
}).listen(oak_port);