I was thinking since some time already about mirroring between elog servers, 
and actually started already some implementation.

The problem with mirroring on the file level does not work. Assume two 
servers "serv1" and "serv2". Then assume that one message gets submitted on 
serv1 and at the same day another message gets submitted on serv2. Now you 
have on both servers a file 030726a.log, but you cannot copy this file 
simply from one server to the other, since you would overwrite the message 
submitted on the other server. Furthermore, you need file level access, 
which is maybe easy between your laptop and your desktop computer, but not 
if the two mirror servers are in different countries. Like in our 
collaboration we have three servers located in Switzerland, Italy and Japan 
(meg.psi.ch, meg.pi.infn.it, meg.icepp.s.u-tokyo.ac.jp), where we cannot 
have direct disk access.

So what I propose is the following mirror scheme:

o Each elog server may contain a list of mirror servers in the configuration 
file

o Each elog server calculates an MD5 checksum from all local messages

o Synchronization between servers can be triggered manually (by clicking 
on "Synchronize") or automatically at a given time and interval

o On Synchronization, the elogd server fetches the MD5 list from the mirror 
server and compares it with the local list

o If a message has been edited remotely but not locally, it's fetched and 
stored locally, same in the other direction

o If a message got edited on both sides since the last synchronization, the 
user is asked to resolve the conflict (keep local or keep remote message)

o If there is a new message locally, its submitted at the remote server, but 
with the same submission date/time as locally, same in the other direction

o If new messages are present on both sides, their message ID is changed so 
that it is unique, then they are copied over. If there are already replies 
to this message, their link (using the message ID) is changed accordingly

So I plan to implement this scheme in the next time. The MD5 checksum is 
already there. If anybody has comments or additional wishes concerning 
mirroring, telling them right now would be great, since I then can 
accomodate them easier during the implementation.

- Stefan