looking for Cyrus mail format documentation

[Phil Howard]

On Tue, Feb 04, 2003 at 09:51:21AM -0500, John Alton Tamplin wrote:

| Henrique de Moraes Holschuh wrote:
| 
| >On Tue, 04 Feb 2003, Phil Howard wrote:
| >  
| >
| >>I wonder how well that method of replication works when both nodes
| >>cannot reach each other, and both are doing updates.  And I wonder
| >>    
| >>
| >They don't.  If they cannot reach each other, at most one of them must allow
| >updates.
| >  
| >
| Which, as far as I know, is how all commercial databases also do 
| replication.  Only those servers involved in a quorum (even if it is 
| because the primary is treated as having more weight) can accept updates 
| -- the other replicas can only be read-only.  Trying to allow arbitrary 
| updates during disconnected operation and then merge the results into a 
| consistent and deterministic state is not just hard, but impossible. 
|  For example, if you allow flags to be set differently on the same 
| message on each node, there is no way to resolve the two updates without 
| discarding at least some of the work of one of the sessions. If you 
| carefully constrain the updates that can be performed during 
| disconnected operation (and for consistency that means even not in 
| disconnected operation), then you can transform the problem from 
| impossible to merely extremely difficult.

However, had message IDs been the RFC822 message ID, then it would have
been possible to receive new mail on each node.  Since the IDs would not
collide, that would be OK.  If you did get the same ID delivered to both
somehow, it should be the same mail.  If not, it violates the RFC, so
then you decide to replace one of them or change one of them and move on.

Deleted mail might be resurrected.

But certainly many other things can be a problem, and in the database
world, replicators can't really know a lot if the particulars about the
data involved, and wouldn't readily be able to do the things you could
get away with for email.

-- 
-----------------------------------------------------------------
| Phil Howard - KA9WGN |   Dallas   | http://linuxhomepage.com/ |
| phil-nospam at ipal.net | Texas, USA | http://ka9wgn.ham.org/    |
-----------------------------------------------------------------