I've tracked down an unexplained EL phenomenon that surfaced in our stats as a false trend in our global stats.

The data I'm looking at specifically is coming from Media Viewer's MultimediaViewerNetworkPerformance_* tables.

Have a look at this graph: https://docs.google.com/spreadsheets/d/1PJsyzAyj74dctGCl4-09L7LS4AMZRh57G56Xc2qZv6w/edit?usp=sharing the big change is on Jan 7th/8th

It shows how many EL events we've recorded, per client-reported country, over the last 90 days. The sampling factor we use has been constant for each wiki over that period. Thus, the distribution shouldn't evolve drastically, aside from seasonal/local trends. Besides the Ukraine spike on a particular date (probably related to world events), the graph before Jan 7th looks like what you would expect. Then, following the outage that happened on Jan 7th, not only the balance is completely changed, but it evolves over time (the US and China are keeping "higher than normal" levels, while the rest seems to slide down lower than pre-7th quantities), showing me that something strange is happening and is probably unresolved.

This balance shifting over time is really problematic for tracking Media Viewer client-side network performance, because Chinese traffic suddenly accounting for a bigger or smaller share of the overall recorded events creates big swings in the global averages/percentiles (since network performance in China is bad).