AJAX is increasingly popular for building web applications and is a central component of the web 2.0 phenomenon. Many of the new google applications including GMail, Google Calendar, Google Reader and Google Maps use AJAX components to create their excellent usability. Other new widely used applications like Flickr, del.icio.us and Digg also use AJAX to create the end user appeal. From an end user and an innovation perspective AJAX has done incredible things for the web and AJAX applications are here to stay. Undoubtably, if built properly, the code used by AJAX apps is scalable. But the question that is being debated widely is “what impact does an AJAX app with a high number of concurrent users have on a web server?”

I found a well rounded summary of this debate by Dion Hinchcliffe and I agree with his conclusion which is that users will ultimately hammer the servers, not Ajax. If you are building AJAX apps this a vital debate to understand because it also has implications for the way in which you will code your presentation layer. The problem (for a webserver) around AJAX is unpredictability of the load not neccessarily the additional volume. Hinchcliffe uses the example of asynchronous calls made to the database everytime the mouse is moved. This may be a killer end user function, but will nail your webserver if you have a high number of users…

Check out the full article.