Replication specifics

David Korpiewski davidk at
Tue May 23 16:48:46 EDT 2006

So I got into a big argument with the people in my department about how 
replication works and I'm seeking some guidance from the community:

(1)The worst fear of any prof here at UMASS is the potential of losing a 
single email.   So my question is this:  If we set up replication, and 
we have to failover to the replica, is there any way to get back email 
that may not have been replicated -- ones that currently only exists on 
the defunct master?   If the replica updates every 10 seconds, then we 
have the potential to lose 10 seconds of email.   Or worse case, the 
sync_client dies and we lose 30 minutes or more of emails before we 

Do other folks out there plan for this "potential for lost emails" or do 
you just failover and if a few messages get lost, you don't worry about it?

(2)Also, is there a master sync transaction log file somewhere that 
specifies what is being done?  In other words, if we failed over, could 
we find a transaction log that would tell us what was not committed and 
then manually run through it to make the updates?  I found the log files 
in "/var/lib/imap/sync", but these are very uninformative:
for example:
SEEN davidk user.davidk
SEEN davidk user.davidk
SEEN davidk user.davidk

it would be nice to see "SEEN update message READ 12020 for 
user.davidk.INBOX", but I don't know if this detailed information is 
somewhere on the system or just resides in memory.

(3) My final question is this:  If we do a manual sync_client update, is 
the update a full copy or is it a "differential" copy?   So I want to 
know if we run a manual sync_client if it is going to overwrite the 
entire replica's mailstore or just search and find what is different and 
just update those portions.

Thank you kindly

David Korpiewski                     Phone: 413-545-4319
Software Specialist I                Fax:   413-577-2285
Department of Computer Science       ICQ:   7565766
University of Massachusetts Amherst

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