I am trying to develop my own live chat system with Ajax, using php/mysql on server side. Simple chat system idea is loading responseTxt into chat frame. However i am also trying to adapt a "user is typing.." feature. I have thought of something like this. When user key press in the input area, mysql column is updated, so in the next ajax get, it will be seen as user is typing. But too much queries with lower intervals can make the system slower i assume. What do you think about this? Can it get bad on high loads or any suggestions for a better way to do this?

I do not use socket servers and do not plan to at this point.