Reading/Web/Lazy loading of images on Japanese Wikipedia

On Tuesday 5th July lazy loaded images was enabled on Japanese Wikipedia for all users. The immediate impact we noticed images on Japanese Wiki Japan article served to users dropped 1.443mb to 142kb.

Bytes saved
The bytes saved varies per article. Articles with more images obviously will be reduced more. We can analyze bytes saved by looking at raw access logs and looking at images with an internal referrer. We can also look at specific pages to gauge impact.

Analysis of weeks worth of data
A database dump of the EventLogging data for Japanese Wikipedia was taken from the period 1st June to 12th July. Data 10 days before and after the change was compared and sample size was not normalized. Given the change was deployed on 5th July at 4:47pm PST the following query was used. select * from NavigationTiming_15485142 where wiki = 'jawiki' and event_mobileMode = 'stable' and event_action ='view' and timestamp > 20160625004700 and timestamp < 20160715004700 This SQL query gave a sample of x rows of data. With the result of the following query, using a Python script the following command was run python navtimingcsv.py jawiki.tsv 20160705004700 10

Analysis of 30 days of data
A database dump of the EventLogging data for Japanese Wikipedia was taken from the period 5th June to 4th August. Data 10 days before and after the change was compared. Given the change was deployed on 5th July at 4:47pm PST the following query was used. select * from NavigationTiming_15485142 where wiki = 'jawiki' and event_mobileMode = 'stable' and event_action ='view' and timestamp > 20160601004700 and timestamp < 20160804004700