Reading/Web/Lazy loading of images and references on Russian Wikipedia

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Russian Wikipedia, a large sized wiki, was the third and final test wiki to have both lazy loaded references and images enabled. It was deployed on 21st July at 4.25pm PST via SWAT window. The intention was to allow comparison with the large sized Japanese wiki which had lazy loading images enabled but not lazy loaded references enabled to inform whether it was worth pursuing lazy loaded references.

Performance Impact[edit]

Sanity checking (10 days)[edit]

To get a general sense of impact after 10 days of the change being live it was possible to compare 10 days prior to the change with 10 days after the change. Using the following SQL query, it was possible to take a database dump of all NavigationTiming events logged for 10 days preceding the change and 10 days following the change.

select * from NavigationTiming_15485142 where wiki = 'ruwiki' and event_mobileMode = 'stable' and timestamp > 20160711002500

This SQL query gave a sample of 167844 rows of data (5 times the amount for the corresponding test in Thai Wikipedia in half the time). With the result of the following query, using a Python script the following command was run

python navtimingcsv.py 10dayRussian.tsv 20160721002500 10

Fully loaded[edit]

Label Sample Size 95th percentile median
Before change 50651 18282.5 2969.0
After change 51508 16533.2 2795.0
Before change (anons) 50601 18273.0 2970.0
After change (anons) 51458 16544.15 2795.0
Before change (http2) 36888 13852.6 2577.0
After change (http2) 37708 12877.65 2437.0
Before change (http1) 13763 28869.7 4381.0
After change (http1) 13800 25066.3 4200.0

First paint[edit]

Label Sample Size 95th percentile median
Before change 28564 7597.0 1534.0
After change 28870 7489.5 1487.0

DomInteractive[edit]

Label Sample Size 95th percentile median
Before change 50651 8199.5 1219.0
After change 51508 7940.9 1140.0

Performance Impact (28 days later)[edit]

Fully loaded[edit]

Label Sample Size 95th percentile median
Before change 134448 18085.3 2943.0
After change 138351 16065.5 2758.0
Before change (anons) 134341 18083.0 2944.0
After change (anons) 138209 16073.6 2758.0
Before change (http2) 97781 13754.0 2550.0
After change (http2) 102257 12732.8 2404.0
Before change (http1) 36667 28191.0 4397.0
After change (http1) 36094 24719.0 4184.0

First paint[edit]

Label Sample Size 95th percentile median
Before change 75418 7534.3 1527.0
After change 78208 7566.0 1459.0

DomInteractive[edit]

Label Sample Size 95th percentile median
Before change 134448 8156.65 1201.0
After change 138351 7921.0 1123.0

Conclusions[edit]

After almost a month of running this experiment it's clear that lazy loading references has minor impact on first paint or DomInteractive, but it does appear to improve things, but it could be argued this is due to lazy loading images. That said the performance improvements on Japanese Wiki were less significant. See Reading/Web/Lazy loading of images on Japanese Wikipedia#Analysis of 30 days of data.

The impact on fully loaded time is more significant on http1 than http2 (improving the 95th percentile by 4 seconds).

More analysis around the data savings at play here are needed.