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Wednesday, 7 December 2011

Speeding up Google Chrome with DNS Pre-Fetching

Why Google Chrome is such a fast browser


I have written a lot about browsers, their intricacies and problems with upgrades and performance including Performance Tweaks for Firefox that you can access from typing "about:config" in the address bar that can increase your browser performance.

Whilst I use Firefox mainly for development at work I have always used Chrome for browsing due to its speed and I find myself using it more and more for development.

Their built in developer tools are just as good as the Firebug add-on which has gone through phases of being slow, buggy and sometimes just plain unusable.

Not only does Google Chrome allow you to inspect elements, modify the DOM on the fly, check resource load times and other useful developer tools it has some other features that many people probably don't even realise.

If you have never done it before just type in "chrome://version/" to your address bar to see details of your current browser e.g

Google Chrome 15.0.874.121 (Official Build 109964) m
OS Windows
WebKit 535.2 (@100034)
JavaScript V8 3.5.10.24
Flash 11,1,102,55
User Agent Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/535.2 (KHTML, like Gecko) Chrome/15.0.874.121 Safari/535.2
Command Line "C:\Users\me\AppData\Local\Google\Chrome\Application\chrome.exe" --flag-switches-begin --enable-print-preview --flag-switches-end
Executable Path C:\Users\me\AppData\Local\Google\Chrome\Application\chrome.exe
Profile Path C:\Users\me\AppData\Local\Google\Chrome\User Data\Default

A nice overview of your browser.

For a list of domains that your browser pre-fetches behind the scenes to speed up load times type the following into your address bar "about:dns" You will see a list of popular domains that you visit along with stats about each DNS pre-fetch.

At the top of the report you will see the 10 pages that Google pre-fetches on startup and it does this to help speed up your browsing experience as it calculates which sites you visit the most so that it can keep these handy in case you want to visit them. By pre-fetching them when you start the browser up it make it look like page load times for these domains are a lot faster than they otherwise would be.

For example my own report shows:

Future startups will prefetch DNS records for 10 hostnames
Host nameHow long ago
(HH:MM:SS)
Motivation
http://blog.strictly-software.com/01:09:02n/a
http://connect.facebook.net/01:09:01n/a
http://pagead2.googlesyndication.com/01:09:01n/a
http://platform.twitter.com/01:09:01n/a
http://s7.addthis.com/01:09:01n/a
http://shots.snap.com/01:09:01n/a
http://twitter.com/01:09:01n/a
http://www.blogger.com/01:09:01n/a
http://www.darkpolitricks.com/01:09:53n/a
http://www.strictly-software.com/01:09:01n/a


All sites I regularly visit and at the bottom of the report I get the following message;

Preresolution DNS records performed for 328 hostnames
Preresolving DNS records revealed non-existence for 5 hostnames.


Another more complex report can be seen with this command "about:histograms/" which will show a number of basic graphs about various DNS checks, lookup speeds and other various stats.


This DNS Pre-Fetching is meant to speed up your browsing experience however sometimes it can cause issues which are noticeable if you ever experience slow page load times along with the words "Resolving Host" in the status bar.

If you have this issue try disabling the pre-fetch feature and compare and contrast page load times with the option on and off with a "ipconfig /flushdns" in between each attempt to make the test fair as well as clearing out any browser cache.

You can do this with either a web developer toolbar, choosing "Tools > Clear Browsing Data" or by selecting "Toolbox > Options > Under the bonnet > Clear browsing data".

You will also find in later versions of Google Chrome they have combined this pre-fetch option with the pre-rendering option under "Predict Network Actions" which is found under "Toolbox > Options > Under The Bonnet > Predict network actions to improve page load performance", 

This option will not only turn on the DNS pre-fetching option it will also aim to speed up searches by pre-loading the first 3 results of any Google search. They do this because statistics apparently show that when a user runs a search they will click on the first 3 links.

Obviously if you don't do that then those page loads have been a waste of time and resources as well as ensuring the HTTP requests are logged in any log file on your server.

However the aim is to speed your browsing up by pre-fetching pages you visit a lot which is a good idea in theory.

You can read more about these two features, pre-fetching and pre-rendering here:

http://blog.chromium.org/2008/09/dns-prefetching-or-pre-resolving.html
http://www.chromium.org/developers/design-documents/dns-prefetching



1 comment:

Tammy said...

Such a great article which Their built in developer tools are just as good as the Firebug add-on which has gone through phases of being slow, buggy and sometimes just plain unusable. In which Google Chrome allow you to inspect elements, modify the DOM on the fly, check resource load times and other useful developer tools it has some other features that many people probably don't even realize. Thanks for sharing this article