AJAX Applications vs Server Load?

Squink asks: "I've got the fun job of having to recode a medium sized (500-1000 users) community site from the ground up. For this project, gratuitous use of XMLHttpRequest appears to be in order. However - with the all of the hyperbole surrounding AJAX, I've not been able to find any useful information regarding server load [Apache + MySQL] when using some of the more useful AJAX applications, such as autocomplete. Is this really a non-issue, or are people neglecting to discuss this for fear of popping the Web2.0 bubble?"

Comments

Depends

[Bogtha]

There isn't any useful information out there because it all depends on what you are doing.

Take a typical web application for filling in forms. One part of the form requires you to pick from a list of things, but the list depends on something you entered elsewhere in the form. In this instance, you might put the choice on a subsequent page. That's one extra page load, and needless complication for the end user. Or, you can save the form state, let them pick from the list, and bring them back to the form. That's two extra page views and saving state. Or, you can use AJAX, and populate the list dynamically once the necessary information has been filled in. That's no extra page views, but a (usually smaller) JSON or XML load.

In this instance, using AJAX will usually reduce server load. On the other hand, something like Google Suggest will probably increase page load. Without knowing your application and its common use patterns, it's impossible to say. Even using the exact same feature in two different applications can vary - autocomplete can reduce server load when it reduces the overall number of searches, but that's dependent upon the types of searches people are doing, how often they make mistakes, how usual it is for people to search for the same thing, and so on.