Google and prefetching

Becca smiling I was certain that I’d blogged about Google prefetching certain search results a couple of months ago, but it turns out that I didn’t.

Basically, on some searches, google instructs your web browser to start downloading the top-most search result before you actually click on the link to that page, meaning that when you do click on the link that page will load that much faster. While this facility is only available for users of the Mozilla based browsers, for those users it results in a an improved user experience. However, as with all good things, there’s also a possible downside - pages being prefetched that the user never actually decides to visit.

Thankfully this has been thought about by google, and the prefetch instruction is only ever applied to the top result for any search, and only then if it has been determined that the greatest majority of users who make that search will click on the top result. This means that only the very best top placed results will get this treatment, meaning less wasted bandwidth for both user and host. Clearly a good thing.

The added advantage of google using the prefetch instruction is that it gives another metric for determining how relevant google thinks that your pages are. In my mind it’s quite an honour for the search engine to determine that you’re not only worth of the top spot, but that you’re also where most people go once they get their results. If you look at a lot of searches you won’t be able to find the <link rel='prefetch'> used to prefetch pages - it’s only on those searches that google is certain you’ll visit that get the treatment. Which is why I’m very happy to announce that for the search “mod_rewrite example” this site has not only got the top spot but is also being prefetched (YMMV, it’s what I’m seeing here)! Now, if only I could get a few of my other search terms up there…

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  1. by greatred on May 11, 2005 08:00 AM

    So - is the prefetch thing any good for preloading image graphics I wonder…

    My own website uses some images for it’s tabs for example (they really should be prettier) - and there’s some :hover-y-ness going on which I use to highlight the tab which the mouse is over. Trouble is that (Firefox at least) only seems to start loading the new images once the tabs have been hovered over.

    I know this preloading stuff is possible in Javascript. But then those who know me will know that I regard Javascript as the Duct-Tape of the Internet (no offence intended to the quality item that Duct Tape is). (Having said that I’m vaguely tempted to use things like MD5 summing passwords in forms before they get posted - which is a Javascript thing - but perhaps acceptable for where https isn’t available and logins need to be more secure than eek plain-text)

  2. by Neil Crosby [TypeKey Profile Page] on May 11, 2005 09:55 AM

    I really wouldn’t use prefetch for preloading image graphics. Why? Because it’s a proprietary technique - after all you wouldn’t consider doing it if Microsoft had come up with the idea, would you?

    The way that I’d be inclined to do the preloading (although I haven’t as yet used this technique) would be to use the “Fast Rollovers” technique.

  3. by greatred on May 11, 2005 01:25 PM

    Aha! Now that’s rather nifty!

    Might even use the more general technique (sprites in a single image) to cut down page load times on my website - when I get back home of course - doing it on paid time in net cafés is a bit time consuming. They don’t have GIMP which is my usual tool :(

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Neil Crosby now blogs at The Code Train and also runs, The Ten Word Review and Everything is Rubbish.