节点。基于事件的comet的周期性ajax请求?

Core features of node.js as far as I understood are (also): event-based structure and very cheap "threads" sleeping. So, it may be really good idea (and probably cheaper) to do not create periodic ajax requests, but to hold events like "user A got a new message" and let user's A connection thread sleep until this event happens.Core features of node.js as far as I understood