James Governor relays a question that sounds important but I think is actively dangerous: do AJAX apps present more of a server-side load? The question is dangerous because it’s meaningless and unanswerable. Your typical Web page will, in the process of loading, call back to the server for a bunch of stylesheets and graphics and scripts and so on: for example, this ongoing page calls out to three different graphics, one stylesheet, and one JavaScript file. It also has one “AJAXy” XMLHttpRequest call. From the server’s point of view, those are all just requests to dereference one URI or another. In the case of ongoing, the AJAX request is for a static file less than 200 bytes in size (i.e. cheap). On the other hand, it could have been for something that required a complex outer join on two ten-million-row tables (i.e. very expensive). And one of the virtues of the Web Architecture is that it hides those differences, the “U” in URI stands for “Uniform”, it’s a Uniform interface to a resource on the Web that could be, well, anything. So saying “AJAX is expensive” (or that it’s cheap) is like saying “A mountain bike is slower than a battle tank” (or that it’s faster). The truth depends on what you’re doing with it. In the case of web sites, it depends on how many fetches you do and where you have to go to get the data to satisfy them. ongoing is a pretty quick web site, even though it runs on a fairly modest server, but that has nothing to do with AJAX-or-not; it’s because of the particular way I’ve set up the Web resources that make the pages here. I’ve argued elsewhere that AJAX can be a performance win, system-wide; but that argument too is contingent on context, lots of context.

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April 19, 2006
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