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

[Bela Ban (JIRA)]

    [ https://issues.jboss.org/browse/JGRP-1484?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12713282#comment-12713282 ] 

Bela Ban commented on JGRP-1484:
--------------------------------

Hi David,

I don't know. I'm very busy with EAP 6.0.1 related issues and RELAY2 (I'm going to push all other issues into a 3.3 and probably release 3.2 soon).
I'll prioritize items when I get to 3.3. Your SEQUENCER related items I'll probably look at first as they don't affect critical code, the other stuff that affect critical code will take longer as I'll have to take a long and hard look (e.g. synchronizing handleView() might have a bad effect wrt deadlocking). 
As I said before, the changes to critical code have a high risk / low benefit (they fix no known bugs), and as I'll need some time to make sure they're correct and don't introduce new bugs, they're at the end of my priority list...

Cheers,

P.S.: I'm not going to discuss this any further via comments on JIRA, let's use email for that (belaban at yahoo dot com).
                
> 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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