P3PC: ValueClick

April 12, 2010 11:44 am | 1 Comment

P3PC is a project to review the performance of 3rd party content such as ads, widgets, and analytics. You can see all the reviews and stats on the P3PC home page. This blog post looks at ValueClick. Here are the summary stats.

I don’t have an account with ValueClick, so my friends over at Zimbio let me use their ad codes during my testing. Since these are live (paying) ads I have to mask the ad codes in the snippet shown here. This means it’s not possible to crowdsource time measurements for these ads.

Snippet Code

Let’s look at the actual snippet code:

1:	<script language=”javascript” src=”http://media.fastclick.net/w/get.media?sid=12345&m=6&tp=8&d=j&t=s”></script>
2:	<noscript><a href=”http://media.fastclick.net/w/click.here?sid=12345&m=6&c=1″ target=”_top”>
3:	<img src=”http://media.fastclick.net/w/get.media?sid=12345&m=6&tp=8&d=s&c=1″ width=300 height=250 border=1></a></noscript>

A quick walk through the snippet code:

• line 1 – Download the get.media script.
• lines 2-3 – NOSCRIPT block in case JavaScript is not available.

Performance Analysis

This HTTP waterfall chart was generated by WebPagetest.org using IE 7 with a 1.5Mbps connection from Dulles, VA. It shows why this snippet has a significant impact on page load time even with just a few HTTP requests and a very small download size.

Keep in mind that valueclick-waterfall.png represents the actual content on the main page. Notice how that image is pushed back to item 6 in the waterfall chart. That’s because the get.media script (item 2) is downloaded using normal SCRIPT SRC tags. This blocks all subsequent HTTP requests in older browsers including IE 6&7. (Here we’re using IE7.)

In addition, the get.media script is served through a redirect in IE (but not in Firefox). For IE a total of three sequential HTTP requests must be completed before the ad is returned. The ad is inserted using document.write, which can further block the main content on the page. In this one page load, the main content (valueclick-waterfall.png) is blocked for 338 + 345 + 163 = 846 milliseconds.

In my analysis of ad snippets I focus only on the ad framework, not on the actual ads. The ValueClick ad framework is very light – just two redirects and one small script that does document.write. Therefore, there are only a few problem areas in which to look for performance improvements, but they’re big:

1. The redirects block the page.

In IE there are two redirects in front of the get.media script. This is two roundrips from the user’s browser to the ValueClick servers and back again. The fact that these redirects don’t occur in Firefox leads me to believe that there’s a workaround for IE. Given that over 50% of Internet traffic uses IE, removing these redirects would have a positive impact on a significant number of users.

2. The get.media script blocks the main content of the page from loading.

It would be better to load the script without blocking, similar to what BuySellAds.com does.

3. The ad is inserted using document.write.

Scripts that use document.write slow down the page because they can’t be loaded asynchronously. Inserting ads into a page without using document.write can be tricky. BuySellAds.com solves this problem by creating a DIV with the desired width and height to hold the ad, and then setting the DIV’s innerHTML.

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Ad networks are an amazing piece of technology. Having so many different companies share such a variety of content across millions of web sites is a real accomplishment. Techniques like document.write and scripts that block have made this possible. But the Web has evolved since these techniques were considered acceptable.

It’s critical that ad providers adopt new web development patterns so they can hit that win-win-win of a fast user experience, publisher content that renders immediately, and ads that appear quickly to drive impressions and click throughs.