I have implemented Google Maps and I'm allowing users to check-in (to mark their location on map with markers). I would like to check for checkins only in radius of 25km around current online user and push new markers on Google Maps around him. I was thinking about using webSockets, not AJAX because it might be too much for server to handle many queries to database. Could someone help me with the logic behind that. I'm not sure how to implement it, how to do it for every single user separately.