Third-party elements such as ad tags, tracking pixels, and widgets are an important component of any website that we visit and build today. As an operator we may not have a direct control on their performance on our web properties, and the impact that has on the end-user experience; yet we still depend on them for achieving specific goals.

Ads are one such crucial component that are a part of the majority of websites. Websites do not have direct control of the ads that get served, yet we include them as they are directly tied to revenue generation.

At around 15:00 EDT on Tuesday, March 13th, Catchpoint noticed an increase in the load times for a number of web pages that we monitor and drops in availability.

The degraded performance was not limited to a single webpage or property but was seen across a number of domains.

When investigating further, we were able to identify the degradation in performance to the ad requests being served from two domains: and


Most of the requests were being called before Document Complete, or the time it takes from the URL request being issued to the browser triggering the “onload” event. Document complete time indicates when a user can fully interact with the webpage. Any delay in the onload event limits the user’s ability to interact with a webpage.

Requests originating from the hosts experience high latency which in turn affected the overall webpage response and document complete time for the webpages. Since these ad requests were called before the “onload event”, the latency affecting the ad requests directly impact the webpage’s performance and the end-user experience.

Investigation into the issue revealed an increase in the amount of time require to establish a TCP connection with the ad server and an increase in the amount of time the server took to respond to the request as well as ocassional HTTP 503 status codes.


Data collected from our real user monitoring solution shows end users experiencing document complete times of 20 to 25 seconds, as opposed to 5 to 10 seconds earlier today.


This is not the first time Google has experienced issues, we wrote about a similar incident in 2014. At this time we suggested website owners place the advertising tags after document complete and load them asynchronously. Sites that delay the loading of ads until after the document complete event will see less of an impact on the end-user experience. With ads loading after document complete, users will still be able to click through to links and interact with the page with minimal impact.

As of the writing of this article, the issue is still ongoing. Google is tracking it and providing updates here.

Author Nilabh Mishra

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