[jboss-jira] [JBoss JIRA] (JGRP-1484) SEQUENCER and merge-views broken

[David Hotham (JIRA)]

    [ https://issues.jboss.org/browse/JGRP-1484?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12705824#comment-12705824 ] 

David Hotham commented on JGRP-1484:
------------------------------------

OK, thanks for letting me know.

Do you have any thoughts on the right fix?  Eg does my suggestion (last couple of sentences of original report) look plausible?  I'd feel much happier embarking on an attempted fix if you could at least go so far as to say that it didn't sound completely idiotic ;-)
                
> SEQUENCER and merge-views broken
> --------------------------------
>
>                 Key: JGRP-1484
>                 URL: https://issues.jboss.org/browse/JGRP-1484
>             Project: JGroups
>          Issue Type: Bug
>    Affects Versions: 3.0.10
>            Reporter: David Hotham
>            Assignee: Bela Ban
>             Fix For: 3.2
>
>
> Here's a new way in which putting SEQUENCER below GMS is broken.
> Start with A having view B|4 [B,A], while B, C and D all have view B|7 [B,C,D].
> Now we start a merge, in which B is coordinator.  B creates the view C|8 [C, D, A, B].
> (I've opened a pull request saying that B surely shouldn't issue a view where the ViewID says that C was the creator.  But I think that this is incidental, and not key to the bug that I'm reporting here).
> Now B sends INSTALL_MERGE_VIEW to B (a coordinator) and A (a merge participant, per Util.determineMergeParticipants).
> B gets this first and broadcasts the new view to [B, C, D].  In particular, B is now not a coordinator.
> Then A gets the INSTALL_MERGE_VIEW, and it too tries broadcasting the new view.  SEQUENCER gets involved, and forwards the broadcast to B (as the coordinator in the old view).  B discards this; it's no longer a coordinator.
> So the new view is not installed at A.  All future broadcasts from A are forwarded to B, who discards them.  The group is fractured, and none of A's broadcasts are delivered.
> I'm not sure what the right fix would be.  I wonder whether things should be arranged so that in a merge:
> -  coordinators behave as today, broadcasting the new view to their own sub-groups
> -  but mere participants do not do this: they should just have the new view installed on them.

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