[Dovecot] A new director service in v2.0 for NFS installations

[Timo Sirainen]

On Wed, 2010-06-16 at 15:19 +0200, Oliver Eales wrote:
> Am 19.05.2010 10:51, schrieb Timo Sirainen:
> > As http://wiki.dovecot.org/NFS describes, the main problem with NFS has always been caching problems. One NFS client changes two files, but another NFS client sees only one of the changes, which Dovecot then assumes is caused by corruption.
> >
> >    host = vhosts[ md5(username) mod vhosts_count ]
> >    
> 
> Hello Timo,
> i am currently playing around with the new director service and i am 
> really looking forward for it in 2.0
> Wouldn't it be better to use a consistent hash function instead of the 
> md5 ?
> So that you would only get a new assignment of users belonging to the 
> failed server and not a "complete remapping".

I thought about it first, but then thought it would only make it more
complex without much benefits.

> With this setup it might be possible to store local indexes in a NFS 
> Backend setting, as the users stay kind of sticky to their server.

Well, this would be a benefit that I didn't think of. :) Maybe it could
be done in future.

> And there would also be no need for the distribution of the currently 
> active mappings within the ring. Maybe only for the state for the servers.

I think it's still needed. Maybe not all mappings, but at least when new
servers are added. For example if server2 handles users A and B, and a
new server3 is added. Now server2 would handle A and server3 would
handle B. But server1 would still need to know that server2 would still
have to handle B until it timeouts (B user can't just be moved to
server3 without killing its existing connections, which doesn't sound
like a good idea).