We had a crash on our database master for English Wikipedia. Domas is restarting it and swapping it out for another master server; should be back online in a few minutes.
In the meantime, Wikipedia in other languages and all other Wikimedia sites remain unaffected.
Update 23:39 UTC: We’re back! Looks like approximately 25 minutes of breakage.
An out-of-memory condition on the database master server ended up killing the MySQL daemon…