Your right we only have a local cache, but since user's are only assigned to one store there will not be any duplication. In general these cached objects are pretty long lived especially in the IMAP or MAPI(Outlook) case where clients connect very frequently to the store for a sync update.
One place we may need to implement a cache on very large deployment would be on the postfix side of things. Since the postfix MTA pool is not tied to any particular domain or set of users each one will need to have access to the entire set of users. To solve this we can just have LDAP caches or we can implement a local cache on each postfix node. Many of us have came from companies that have deployed carrier/ISP scale mail systems. In this case we are talking terabytes of data and 10's of millions of LDAP entries and mailboxes. So we've seen and worked on some huge deployments.
Maybe you can share with us your plans and the size of user base you plan to support.
In any case with all contributions we will evaluate them for inclusion in a future release. In this case we'd need to do some heavy perf testing in our solution lab to see if the extra component (memcached) gives us enough benefit in terms of performance. I'm sure you'll do some of this testing yourself so you can get an idea of any benefit ahead of time.  |