On Sun, 19 Sep 2004, David Lang wrote:
5. Active/Active
designate one of the boxes as primary and identify all items in the datastore that absolutly must not be subject to race conditions between the two boxes (message UUID for example). In addition to implementing the replication needed for #1 modify all functions that need to update these critical pieces of data to update them on the master and let the master update the other box.
We may be talking at cross purposes (and its entirely likely that I've got the wrong end of the stick!), but I consider active-active to be the case where there is no primary: users can make changes to either system, and if the two systems lose touch with each other they have to resolve their differences when contact is reestablished.
UUIDs aren't a problem (each machine in a cluster owns its own fraction of the address space). Message UIDs are a big problem. I guess in the case of conflict, you could bump the UIDvalidity value on a mailbox and reassign UIDs for all the messages, using timestamps determine the eventual ordering of messages. Now that I think about it, maybe that's not a totally absurd idea. It would involve a lot of work though.
Pro:
best use of available hardware as the load is split almost evenly between the boxes.
best availability becouse if there is a failure half of the clients won't see it at all
Actually this is what I do right now by having two live mailstores. Half the mailboxes on each system are active, the remainder are passive.
-- David Carter Email: [EMAIL PROTECTED] University Computing Service, Phone: (01223) 334502 New Museums Site, Pembroke Street, Fax: (01223) 334679 Cambridge UK. CB2 3QH. --- Cyrus Home Page: http://asg.web.cmu.edu/cyrus Cyrus Wiki/FAQ: http://cyruswiki.andrew.cmu.edu List Archives/Info: http://asg.web.cmu.edu/cyrus/mailing-list.html
