Reading/Web/Projects/Barack Obama in under 15 seconds on 2G/Quarter 3

Impact on Barack Obama
At the start of the quarter, 4th February, we were shipping 188.5kb of html and 1.4mb of images to our users for the Barack Obama article. As of April 5th, for that page we are shipping 155k of HTML and 545kb of images. Note, that between these two dates there were minimal changes to the article and the images were changed resulting in a bloat of 11kb to the article but this was not taken into account in these measurements.

Impact so far globally
Globally, at the start of the quarter (4th Feb) for the 95th percentile of anonymous users a page took 14.4s to load.

Now it takes 12.8s.

This 11% improvement could possibly be attributed to the removal of srcset attributes and removal of navbox HTML.

Removal of srcset attributes
https://www.mediawiki.org/wiki/Reading/Web/Performance/Removal_of_srcsets

Reduced bytes shipped to users.

Unclear how many exactly can be attributed to this but we can observe post change that: Pages load quicker
 * 50% less bytes shipped for Barack Obama
 * 0.6gb less data shipped by our servers/to our users
 * 4.56% improvement to median fully loaded time for Barack Obama article for 2G simulated connection
 * Note: Don't trust our 2G simulated connection to actually be 2G. I think in reality connections are slower and we might be saving more.

Removing navboxes and html marked with nomobile
https://www.mediawiki.org/wiki/Reading/Web/Projects/Performance/Removal_of_secondary_content_in_production

Page load quicker on English Wikipedia Other wikis slower
 * 4.28% improvement on median fully loaded time for Barack Obama on 2G simulated connection
 * 5.13% improvement to fully loaded time on English Wikipedia for 95th percentile for global traffic
 * Only 0.45% improvement to fully loaded time on all wikis. Note that not all wikis use the navbox class/template.
 * 10% improvement for 95th percentile on Japanese Wikipedia
 * 6% improvement to first paint for English Wikipedia for 95th percentile of global traffic.

It's not clear why or how, but wikis such as Hebrew Wikipedia and German Wikipedia seem to have slower fully loaded time since the change. It's doubtful that this simple change could have had such negative impacts on fully load time.

Bytes were saved but we are unable to measure impact on server load/bytes shipped to users.

Taking the Barack Obama article as an example it's clear that we saved bytes for users on that page.

That said, we need to identify a way to accurately measure the global bytes saving for changes in HTML. Potentially we may want to explore recording this in NavigationTiming.