Socket.io for checking updates from database

If you don't want to do any polling on the database you can use the postgresql database which support listen/notify. You will be notified immediately when there is a modification on the table.

You can run your code in timer's event handler on server.

The code below checks database for new message for every 5 seconds and emits event if necessary

io.sockets.on('connection', function (socket) {  socket.emit('greeting', 'Hello');  setInterval(5000,function(data){  var uid = data['uid'];  var q = "SELECT * FROM messages WHERE user_id="+uid+" ORDER BY id DESC LIMIT 1";  connection.query(q, function(err, rows, fields) {      if (err) throw err;      if (rows[0].id > prev_id){        socket.emit('new_message',rows[0]);        prev_id = rows[0].id      }    });  });});

As alternative way I think you could implement message queueing using redis with the fast node_redis client. It has built-in pubsub semantics.

Look at Redis. It is fast NoSQL key-value storage which you can use to organize fast message queueing. Use node_redis npm module to communicate with it. Read this reference