Async IO Server with Blocking DB

[looking for]

Hi

We are thinking about building a webservice server and considering
python event-driven servers i.e. Gevent/Tornado/ Twisted or some
combination thereof etc.

We are having doubts about the db io part. Even with connection
pooling and cache, there is a strong chance that server will block on
db. Blocking for even few ms is bad.

can someone suggest some solutions or is async-io is not at the prime-
time yet.

Thanks