Reading/Web/Projects/Performance/Lazy loading images

Lazy loading images was enabled on the production beta channel on the 24th March. As an example, this led to the overall bytes served to users for images on the Barack Obama article dropping from 657kb to 169kb.

Early data shows this had a positive impact on the 95th percentile of beta anonymous and authenticated users in our global metrics but impact was less clear in our controlled tests on Barack Obama.



Predicting impact on stable
Static files emulating the lazy loaded images experience vs the current experience were uploaded to the cluster.

First view load was 38.541s for the current experience of the Barack Obama page on a 2G browser. With images lazily loaded under the same conditions first view load was 25.210s - a saving of around 13s and a 35% speed improvement.

Interestingly, our own webpagetest jobs simulating a 2G connection record fully loaded time as already being around the 25s mark. When run here the first load time was 22.787s for the current experience and 18.942s with lazy loaded images - a saving of around 4s - a 17% speed improvement.

The speeds simulated are supposed to be the same, so it is currently not clear which is a more accurate indication of how this change will benefit 2G users and this is being investigated.