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Simon Willison’s Weblog

DNS Prefetching Implications. deviantart use a subdomain per user, which meant the DNS prefetching feature in Firefox and Chrome was costing them an extra 10 billion DNS queries per month. Disabling it with a meta tag saves them $1600/month in DNS service charges.

Posted 9th March 2011 at 10:54 pm

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8 comments

  1. Companies spend a lot of money to pay software developers to optimize page load time by fractions of a second. On the other hand, they refuse to pay for DNS prefetching which speeds page load time by seconds in some cases. Go figure.

    arty - 10th March 2011 07:29 - #

  2. @artsy,

    I don't think that's what the article says at all, they describes a technique which lets you shut down prefetching "certain parts of the page", you don't necessarily lose the benefits of prefetching, you can selectively turn it off for particular sets of links which you don't want their DNS entries to be batch prefetched.

    Say hypothetically, if twitter gave each user their own subdomain, the browser would prefetch DNS entries for every listing of a person you followed and the subdomain of every user's tweet in your stream. Conceivably hundreds of subdomains getting prefetched on every page with the majority being wasted. In that circumstance, it is easy to see that DNS prefetching is NOT an optimization but a diminishment of the browsing experience.

    huxley - 17th March 2011 21:30 - #

  3. The conclusion is incorrect. It saved pinkbike $1600/month on 350m queries. It saved 10 billion queries on dA which is a larger saving.

    In the dA case, there are lots of subdomains on the page, BUT the page is rendered dynamically when the subdomain is clicked, and the ajax call goes to the www, so there is NEVER a saving due to dns prefetching. The subdomains are there as a fallback for non js users. So you see this is a case where DNS prefetching is ONLY a negative impact on performance and also on the pocket book.

    Radek - 17th March 2011 23:08 - #

  4. I don't think that's what the article says at all, they describes a technique which lets you shut down prefetching "certain parts of the page",

    henrytracy - 14th October 2011 09:36 - #

  5. http://boyhairs.edublogs.org a lot of money to pay software developers to optimize page load time by fractions of a second. On the other hand, they refuse to pay for DNS prefetching which speeds page load time by seconds in some cases. Go figure.

    henrytracy - 14th October 2011 09:36 - #

  6. Excellent read, I just passed this onto a colleague who was doing a little research on that. And he actually bought me lunch because I found it for him smile So let me rephrase that: Thanks for lunch! forex

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