Is RSS Auto-discovery Slowing Down Your Site

RSS Auto-discovery is a nifty feature within firefox that was also added recently to Internet Explorer. I'm not sure about browser support, but the idea is very simple - include a small tag in the head section of your document pointing to your RSS file. When the tag is noticed by firefox, a little icon appears on the address bar and it gives the user the option of subscribing to the feed.

Interestingly enough, I discovered that when that link is present, the RSS file will be downloaded by firefox prior to even the CSS file being loaded. If you are serving RSS statically or from a cache, and that file is relatively small you may not notice anything at all.

If your RSS file is large or is dynamically generated, this additional download can be a little bit rough on your users - particularly dial-up users. In my case, my vBulletin out-of-the-box RSS feed actually is cached, albeit rather inefficiently, but the struggle was due to size - the RSS feed is 20K! That means that people surfing through the forums are regularly downloading documents they aren't using, and for a dialup user this presents a delay of 4.5 seconds!

There are several reasons for concern -

• HEAD linked elements must be downloaded prior to a page being displayed
• HTTP Requests to a server are limited to two (or four depending on your browser) at a time, meaning that this file must be downloaded prior to other important page elements
• The dynamic nature of the request - even with caching - unnecessarily strains the web server

You may argue that a single 20K download should happen quickly and would not cause any harm, ignoring the problems for dialup users. Consider the situation where your site was slashdotted, dugg, or received a large influx of traffic via some other social networking venue. Your server would literally be handling double the traffic that it needed to - and therefore it would be much more likely that your server would not be able to handle the load. Removing the auto-discovery link and placing a small link on-page for users of RSS data presents a small inconvenience to a very small segment of end users.

Removing that link from my forum, decreased the time to page display from 6.25 to 1.87 seconds for a 56K modem user - a time savings of 70%, it decreased the dynamic page burden by 50%, and decreased the total data transfer for an initial visitor by 20%, and decreased the total data transfer for a repeat visitor by 83%.

It may not sound significant to simply remove a link to an rss file, but under heavy load conditions the savings are too large to ignore.