All of these things are possible with Tornado by using simple blocking calls and running more than one instance of the Tornado application behind a reverse prox

All of these things are possible with Tornado by using simple blocking calls and running more than one instance of the Tornado application behind a reverse proxy. If one instance blocks, then there are other instances of the application to handle new requests. FriendFeed uses Tornado with MySQL (I learned this from Brett Taylor's blog). It seems to work.