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How does google adsense work

Since the day I started streaming ads from google through their AdSense program I have been doing some research on how this whole process works and how does google know what ads to display on your pages. And in this learning process I learned some tricks that help in web site optimization for more effective ad positions and content. And also learned that a single mistake can cause lot of problems in displaying right ads for the right content.

Before I explain any more on this topic, I need to clarify that I do not work for Google. So all the information that I am publishing is result of my long time research and analysis. Google keeps its process and algorithm secrets so only thing we all can do is analyze our day to day experience and come up with some conclusions.

Your site's interaction with adsense program starts when you publish a web page that has google adsense javascript code embedded in it. If you notice the source of your page, you will see that there is an IFRAME sitting on your page where you inserted adsense javascript. By using IFRAME, the script issues separate requests to google's syndication service which sends a response back to the page. This reponse is an HTML page which has the ads relative to the context of that page. By using IFRAME, google does not block display of rest of your page. As the response from the syndication service comes, the content in that IFRAME gets displayed. Some time you will notice if connection is too slow or there is network congestion and an image ad is being streamed you have broken image links on the page. This some time happen because the response for that ad did not get doenloaded to your browser. So this is pretty much overview of how advertisements gets displayed on you page.

How does google know the context of content?

When you publish a new page and it is accessed the first time, google does display ads on the page although the syndication service is seeing it the first time. And half of those ads will be relevent to the context of the page. And some of the ads will be completely irrelevant to the page. For example I published a programming article and when I viewed it the first time there were ads related to real estate. How does it happen? Here is what I think how it works. Google fetches the page quickly and looks at title, description and keywords meta tags. And then quickly grabs the ads related to those and streams them to your page. And there are certain advertisers who pay google to display their ads when there is no other ad to display on the pages. And it seems that google does pay little attention to the URL of the page. If the URL has some words that make sense, it will use that as context too.

Once you page has been viewed atleast once, its URL gets into Google's MediaPartner bot's feed database. This is a separate crwler that is used by google's advertising framework. It is not the same as search engine crawler GoogleBot. MediaPartner-Google/2.1 bot probably is optimized more towards determining context of the pages instead of indexing all the content for search. Does MediaPartner bot and GoogleBot share the information. I think MediaPartner bot does help GoogleBot in notifying new URLs coming up on the internet. These days you will notice that pages get into search engines faster than they used to be. I think AdSense progrms have played a big part in it.

Once your URL is in MediaPartner bot's feed database, the crawler comes to your URL and gets the content and feed it to google's analysis servers where page context gets decided and the URL gets assigned to keywords, categories etc. And when a user views that page, the ad server quickly matches the context of that page with the advertisements which have asked to be displayed when pages with that context, keywords etc. gets viewed. Google does not fetch the content of your page everytime it is viewed.

Now you must be asking how often does google refreshes the context of the page. Probbaly you are thinking it gets refreshed every week or so. Well it does not look like that way and we have first hand expereince of it. If you wish you can contact us and we can probably show you a proof of it too. MediaPartner bot's indexing seems to work at similar frequencies as search engine's bot. And that index gets refreshed after more than a month. So once your page has been fetched by MediaPartner bot and categorized then it is going to stay in the database till next index refresh happens. So when you are publishing pages make sure that you have right content on it. Otherwise your users will be seeing ads on the page which are totally unrelated to the page even though you corrected the content of the page after you realized your mistake.

There is a very interesting finding of my research. While I was writing articles and testing on the local machine, there were lots of ads being displayed for web hosting, sql server hosting, email hosting, seo etc. And I was not writing about them at all. Then I relaized that I am accessing the pages using "http://localhost". And syndication service is smart to relaize that I am viewing pages on local machine and I am in middle of testing. So they give me ads for hosting providers incase I have not hosted my site anywhere.


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