I updated translatewiki.net code two days ago (after a two week break).
Today I started getting reports that edits are going to wrong pages. I was not able to produce myself, but I found some history which looks wrong.
Click to view the version of December 5th 2017 [?oldid=XXX now shows correct content for this language because cache was purged]. It was supposed to be a two byte change overall (with comment saying some word is replaced). However looking at the diffs or viewing it directly we see a completely unrelated text:
Same unrelated text is also seen on https://translatewiki.net/w/i.php?title=MediaWiki:Cx-notification-deleted-draft/fr&diff=9049005&oldid=9046073
- Wrong content is displayed in page histories diffs both in translatewiki.net and Wikimedia wikis with Translate
- Wrong content is getting exports (not 100% if caused by this)
- It is determined that database is okay, and issue lies with caching of contents.
- It is suspected that there is something wrong with WANObjectCache::getMultiWithUnionSetCallback that causes wrong contents to be cached.
- The problematic caching has been disabled to prevent further corruption of caches. This has been deployed to translatewiki.net and Wikimedia wikis
- Caches have been purged on translatewiki.net (multiple times)
- Caches have not been purged on Wikimedia wikis
- Badly cached entries still findable on translatewiki.net. This hints that there may be other causes, or issues with the cache purging strategy. Running the purge script again DOES make the wrong content go away, so maybe there is yet another place where wrong content can be cached, which then populates to these caches?