key expiration for many memcached clients and DB stress

[Victor Gumayunov]

Hello everybody,
please advise how to solve our problem.

We're using memcached in our web project.
The site is actually a frond-end to some database.
Since number of users is very high, we cache DB info in memcached.
But when some memcached key expires, many users simultaneously rush to
the DB server stressing it to the edge.

Obvious solution is to notify in some way 1 web client that certain key
is about to expire, so the client re-fetches it from DB and updates in
memcached, while other clients still use cached value until it is
updated by notified client.

We tried several client-side approaches to implement this scenario,
but no one gives 100% good result.

So we changed server's logics for key processing.
Our modified memcached recognizes specially formatted key names
and does what I described above (formatted key name contains
various parameters for such a behavior).

This works almost well, but now we (of cause) run into expected
problem that our memcached server cannot be updated when new
memcached version is released.

Can you advise how to solve our problem (key expiration for many
memcached clients simultaneously, which causes DB stress) without
patches and various complicated client-side tricks?

Thanks in advance.