For several weeks now, at least one user reports to be unable to use Special:RecentChanges on translatewiki.net, because it results in a 504 Gateway Time-out error. https://translatewiki.net/wiki/Thread:Support/Special:RecentChanges
This particularly affects translators, who need to know what's going on in their language. Operating a wiki without RecentChanges is like operating a railway station without signs for timetable or directions.
The problem was surfaced when the entire wiki was switched to hhvm, which is set up to use a 10 seconds time out instead of the traditional 30 seconds. Database queries are often longer than that.
Niklas was kind enough to spend some 30 min extracting some data to assess the frequency of errors.
12.08 <+Nikerabbit> 94 200
12.08 <+Nikerabbit> 21 302
12.08 <+Nikerabbit> 17 404
12.08 <+Nikerabbit> 12 502
12.08 <+Nikerabbit> 10 499
12.08 <+Nikerabbit> 1 504
12.12 <+Nikerabbit> looking at the user agents there are at most 5 real users who can have encountered *any kind* of error for special:rc
12.16 <+Nikerabbit> Nemo_bis: those users have encountered an issue that the page has been failed to deliver. it does not mean that is a permanent error