[webkit-dev] Implementing WebTiming as a part of HTML5

Lenny Rachitsky lenny.rachitsky at webmetrics.com
Tue Feb 2 13:21:04 PST 2010

I¹d like to address the question by Darin, regarding the question of
feedback and whether anyone is planning to build something to use this new

I work for a company that sells a web performance monitoring service to
Fortune 1000 companies. To give a quick bit of background to the monitoring
space, there are two basic ways to provide website owners with reliable
performance metrics for their web site/applications. The first is to do
active/synthetic monitoring, where you test the site using an automated
browser from various locations around the world, simulating a real user. The
second approach is called passive or real user monitoring, which captures
actual visits to your site and records the performance of those users. This
second approach is accomplished with either a network tap appliance sitting
in the customers datacenter that captures all of the traffic that comes to
the site, or using an ³event listener² javascript timer which times the
client side page performance and sends it back to a central server.

Each of these approaches has pros and cons. The synthetic approach doesn¹t
tell you what actual users are seeing, but it consistent and easy to
setup/manage. The appliance approach is expensive and misses out on
components that don¹t get served out of the one datacenter, but it sees real
users performance. The client side javascript timing approach gives you very
limited visibility, but is easy to setup and universally available. This
limited nature of the this latter javascript approach is the crux of why
this ³Web Timing² draft is so valuable. Website owners today have no way to
accurately track the true performance of actual visitors to their website.
With the proposed interface additions, companies would finally be able to
not only see how long the page truly takes to load (including the
pre-javascript execution time), but they¹d also now be able to know how much
DNS and connect time affect actual visitors¹ performance, how much of an
impact each image/objects makes (an increasing source of performance
issues), and ideally how much JS parsing and SSL handshakes add to the load
time. This would give website owners tremendously valuable data is currently
impossible to reliably track.
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