https://meta.wikimedia.org/wiki/Special:GlobalRenameProgress/MB has been stuck for nearly four days now. The rename on enwiki is stuck at "In progress" but doesn't seem to actually be progressing. All other wikis have been renamed successfully.
All three job retry attempts failed with a lock wait timeout (twice when changing usernames in page revisions, once on SELECT wl_user, wl_notificationtimestamp FROM watchlist WHERE wl_namespace = '2' AND wl_title = 'Mb66w' FOR UPDATE - how on Earth can you get lock contention on that?).
Failed jobs are retried by the job queue; I'm not sure if there is a way for a job to tell that it has failed for the last time. Maybe renameuser_status could get a failure count column?
Nope, a single case of failed rename in two weeks is not an emergency. This is a puppet patch so I can get it deployed in tomorrow's SWAT (or someone can just go on and merge it I guess). I'm working on fixing the affected account.