Re: Funding Cyrus High Availability
On Sat, 18 Sep 2004, Ken Murchison wrote: I'm not sure that IMAP is ameniable to active-active: the prevalence of UIDs in the protocol means that it would be very hard to resolve the inconsistencies that would occur if a pair of machines ever lost touch. Right, I was assuming that active-passive is what we would probably get, I was just taking the pulse of the community. In the past I have attempted to steer things internally at work toward active-active solutions, but I think expecting that here will result in an unrealistically complex solution to deploy, if implemented. --- 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
Re: Funding Cyrus High Availability
David Carter wrote: On Fri, 17 Sep 2004, Ken Murchison wrote: Actually what I was really asking, is are people looking for an active-active config and an active-passive config? I'm not sure that IMAP is ameniable to active-active: the prevalence of UIDs in the protocol means that it would be very hard to resolve the inconsistencies that would occur if a pair of machines ever lost touch. Right, I was assuming that active-passive is what we would probably get, I was just taking the pulse of the community. I would be happy to be proved wrong: active-active is clearly better from a system administrator perspective :). -- Kenneth Murchison Oceana Matrix Ltd. Software Engineer 21 Princeton Place 716-662-8973 x26 Orchard Park, NY 14127 --PGP Public Key--http://www.oceana.com/~ken/ksm.pgp --- 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
Re: Funding Cyrus High Availability
On Fri, 17 Sep 2004, Ken Murchison wrote: Actually what I was really asking, is are people looking for an active-active config and an active-passive config? I'm not sure that IMAP is ameniable to active-active: the prevalence of UIDs in the protocol means that it would be very hard to resolve the inconsistencies that would occur if a pair of machines ever lost touch. I would be happy to be proved wrong: active-active is clearly better from a system administrator perspective :). -- 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
Re: Funding Cyrus High Availability
Hi, Ken Murchison wrote: Question: Are people looking at this as both redundancy and performance, or just redundance? for performance we already have murder, what we currently lack is redundancy. once we have redundancy then the next enhancement is going to be to teach murder about it so that it can failover to the backup box(s) as needed, but for now simply having the full data at the backup location would be so far ahead of where we are now that the need to reconfigure murder for a failover is realitivly trivial by comparison. Actually what I was really asking, is are people looking for an active-active config and an active-passive config? My vote is certainly for active-active... And if feasible, I would also choose to have an equal role for both servers. I think in this stage (altough maybe not if David's patch is copied entirely) that this would be not so much work extra, but when adding it later it seems much more work to me. (It's just a matter of design I suppose: having two backlogs and synchronising them to the other host. This is also what you want with an active-active situation, it shouldn't matter who you're talking to.) David Carter wrote: In my sketch above (really not sure if it works of course) where both have something like a backlog you can like "tail" that backlog and push the update as soon as possible to the second machine. You solve the thing you mention with delays while pushing updates to two servers at the same time. Yes, that's exactly how my code works. Asynchronous replication (which Ken called lazy replication) is fairly easy to do in Cyrus. Synchronous replication, where you only get a response to an IMAP/POP/LMTP command when the data is safely committed to the replica, would involve a much more substantial rewrite of the Cyrus code. I don't know the exact benefits of that solution, but I can also imagine that this raises problems if one server is down. (You have to use a backlog then anyway.) I think I care more about having two servers active (with the option of active-down) and a good recovery mechanism then if the synchronisation is lazy or not ;-) (and I think that it might be easier to recover (when e.g. both servers crash) with a backlog, but that's really up to the programmers.) Bye, Paul --- 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
