On Fri, Feb 26, 2010 at 7:55 PM, Alan Jones <falanclus...@gmail.com> wrote: > On Fri, Feb 26, 2010 at 2:57 AM, Andrew Beekhof <and...@beekhof.net> wrote: >> >> Not only safe but essential, otherwise B would kill A for no reason. >> Transitional memberships are just corosync's way of saying "i;m still >> working, but this is what I have so far". > > The best explanation I've found for the transitional membership is in: > "Group Communication Specifications: A Comprehensive Study" 1999 > Vitenberg/Chockler/Keidar/Dolev > > It relates to support for positionable memberships. In Pacemaker it might > be the case that for B to > become DC and modify the CIB without A, B would have to STONITH A. If that > is the case, then when > A gets a new membership including B he can assume that B has not modified > the CIB without him. > > However, I'm not convinced that he can assume that B has received all the > same messages during > the transition.
He doesn't have to. The CIB contains version information that it uses to resolve conflicts and ensure everyone is up-to-date. The only time you'd have trouble is if you made different changes to both A and B while they couldn't see each other. And that would be a strange thing to do. In that case, the cluster picks one and archives the other. > If Pacemaker clobbers B's CIB after a new membership then > it doesn't matter. >> >> > How is the CIB replicated? >> Thats not related to the above question is it? >> > It is. I'm trying to understand when and how copies of the CIB are > synchronized. To that end > I've created a simplified graph of crmd's finite state automata using > graphviz which others might > find useful (attached). I'll try to break this question up: > 1. When the CIB is updated, are the none DC copies updated by coping the > entire CIB or with a message that represents only the change? > 2. Is the update sent to each copy separately or using corosync's multicast? > 3. When a new DC is elected, what steps are taken to assure that it's copy > of the CIB is up-to-date? > For example, a new member that has not finished incorporating the CIB should > not be eligible for the role of DC; how is this accomplished. > > Alan > > > _______________________________________________ > Pacemaker mailing list > Pacemaker@oss.clusterlabs.org > http://oss.clusterlabs.org/mailman/listinfo/pacemaker > > _______________________________________________ Pacemaker mailing list Pacemaker@oss.clusterlabs.org http://oss.clusterlabs.org/mailman/listinfo/pacemaker
