How do I make scalable PHP for rapid Ajax requests?

I have a program in which an Ajax request goes out to a PHP script that does all the behind the scenes stuff of grabbing the data 开发者_如何学JAVAfrom the database and then returning it as responseText to be pasted into my HTML to update the page without refreshing. I do this request once every 250 milliseconds (so that means I get 4 hits to the PHP script per second for every user on the HTML page firing the Ajax requests.) I am already seeing the PHP crash with a few computers on at the same time, so I'm guessing the problem has something to do with the PHP getting a lot of requests. Is there a way to do these requests so that a lot of users can get on without this scalability issue coming into play?

First of all firing that much ajax requests ain't a good idea. when the number of users increases, the server load will increase exponentially serving requests. Second thing you need to consider the possibilities of scaling the application and database. I guess you might be returning json_encoded data from server, else make it so.

4 r/s is.. nothing for PHP. So in a short: in order to make PHP scalable; make your code scalable.