Node.js (WebSocket with MongoDB updates)

webSocketServer.js

var http = require('http');
var MongoClient = require('mongodb').MongoClient;
var server = require('websocket').server;

startMongoDBConnection();

function startMongoDBConnection(){
  MongoClient.connect('mongodb://localhost:27017/sparta', function(err, db) {
    startWebSocketServer(db);
  });
}

function startWebSocketServer(db){
  var connections = new Set(); // Storage of connections
  var countries = {$in: ['de','es','fr']}; // Filter
  var lastModification = 0; // Greater modified

  var socket = new server({
    httpServer: http.createServer().listen(8008)
  });

  console.log("WebScoket running on ws://localhost:8008");
  
  setLastModified();
  initInterval();

  socket.on('request', function(request) {
    var connection = request.accept(null, request.origin);
    
    connections.add(connection);

    db
      .collection('id_country_hour')
      .find({country: countries}, {country: 1, count: 1, hour: 1, _id: 0})
      .toArray(function(err, docs){
        connection.send(JSON.stringify(docs));
      });

    connection.on('close', function() {
      connections.delete(connection);
    });
  });

  function initInterval(){
    setInterval(function(){
      db
        .collection('id_country_hour')
        .find({country: countries, modified: {$gt: lastModification}}, {country: 1, count: 1, hour: 1, _id: 0})
        .toArray(function(err, docs){
          if(docs.length > 0){
            connections.forEach(function(connection){
              connection.send(JSON.stringify(docs));
            });
            setLastModified();
          }
        });
    }, 1000);
  }

  function setLastModified(){
    db
      .collection('id_country_hour')
      .find({$query:{},$orderby:{modified:-1}}, {modified:true}, {limit:1})
      .toArray(function(err,docs){
        lastModification = docs[0].modified;
      });
  }
}

you're requesting to db on every socket request. what is the difference from classic xhr request?