Last modified: 2012-11-01 00:28:45 UTC
Currently, we store user sessions in memcached, not in a database or other persistent store. More importantly, we don't replicate. One consequence of this is that we can't freely redirect users between two different data centers, since memcached doesn't work well over long-distance links. Our ideal solution would involve some sort of replicated store. Project page: http://www.mediawiki.org/wiki/Replicated_session_handling
Moving this back to Tim for now. We'll figure out a plan and who will implement this in the coming weeks.
The dev work for this is done (Redis integration complete). Ops is in the process of deploying.