Is it OK for users to use either of a pair of replicated servers ?

[Adam Tauno Williams]

On Fri, 2013-02-01 at 16:15 +0000, John wrote:
> Further to my last message, I've updated my master so now both servers 
> report the same version:
> version    : v2.4.17 d1df8aff 2012-12-01
> I'd like to understand some error messages that I am getting and what I 
> should do to resolve them...
> On the replica:
> syncserver[8816]: higher last_uid on replica user.myuser - 57628 < 57629
> syncserver[8816]: higher modseq on replica user.myuser - 36186 < 36187

A modseq is very much like an etag or a ctag in HTTP/WebDAV.  It is a
value that gets incremented with every change.  So the the modseq on the
slave is greater than the modseq on the master... something is out of
sync.

> On the master:
> sync_client[5197]: MAILBOX received NO response: IMAP_MAILBOX_CRC 
> Checksum Failure
> sync_client[5197]: CRC failure on sync for user.myuser, trying full update
> sync_client[5197]: SYNCNOTICE: record mismatch with replica: user.myuser 
> more recent on master

Aren't you connecting to the slave and making changes?  That would make
sense then, the master and the replica are constantly getting
out-of-sync.  Replication is one-way.

> Despite these messages, my replication appears to be working but I can't 
> as yet be 100% sure. I'd like to understand the above and try and stop 
> them if I can...

Because it is constantly recovering, as these messages indicate.  2.4.x
replication is quite reliable and recovers from inconsistencies most of
the time.

> I can't find any documentation detailing what the above means, and I'm 
> not that familiar with the internals of the imap server, so I'd really 
> appreciate some pointers...

-- 
Adam Tauno Williams  GPG D95ED383
Systems Administrator, Python Developer, LPI / NCLA